Reactive extraction of metals, energy storage and delivery systems, and associated articles, systems, and methods

Abstract

Reactive extraction of metals, energy storage and delivery systems, and associated articles, systems, and methods are generally described. Certain aspects related to energy storage and delivery systems that employ metallic sodium and / or metallic lithium and / or metallic potassium as an electrochemically active material.

Description

[0001] REACTIVE EXTRACTION OF METALS, ENERGY STORAGE AND DELIVERY SYSTEMS, AND ASSOCIATED ARTICLES, SYSTEMS, AND METHODS

[0002] RELATED APPLICATIONS

[0003] This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 63 / 697,798, filed September 23, 2024, and entitled “Energy Storage and Delivery Systems and Related Articles and Methods”; U.S. Provisional Patent Application No. 63 / 700,058, filed September 27, 2024, and entitled “Reactive Extraction of Metals and Associated Articles, Systems, and Methods”; U.S. Provisional Patent Application No. 63 / 706,538, filed October 11, 2024, and entitled “Reactive Extraction of Metals and Associated Articles, Systems, and Methods”; U.S. Provisional Patent Application No. 63 / 716,103, filed November 4, 2024, and entitled “Energy Storage and Delivery Systems and Related Articles and Methods”; U.S. Provisional Patent Application No. 63 / 716,113, filed November 4, 2024, and entitled “Reactive Extraction of Metals and Associated Articles, Systems, and Methods”; U.S. Provisional Patent Application No. 63 / 811,402, filed May 23, 2025, and entitled “Energy Storage and Delivery Systems and Related Articles and Methods”; and U.S. Provisional Patent Application No. 63 / 811,371, filed May 23, 2025, and entitled “Reactive Extraction of Metals and Associated Articles, Systems, and Methods,” each of which is incorporated herein by reference in its entirety for all purposes.

[0004] TECHNICAL FIELD

[0005] Reactive extraction of metals, energy storage and delivery systems, and associated articles, systems, and methods are generally described.

[0006] SUMMARY

[0007] Reactive extraction of metals and associated articles, systems, and methods are generally described. Energy storage and delivery systems and related articles and methods are also generally described. Certain aspects relate to energy storage and delivery systems that employ metallic sodium and / or metallic lithium and / or metallic potassium as an electrochemically active material. The subject matter of the present disclosure involves, in some cases, interrelated products, alternative solutions to a particular problem, and / or a plurality of different uses of one or more systems and / or articles.

[0008] #14431536vl Certain aspects relate to a method. In some embodiments, the method comprises initiating contact between a reducing reagent and a metal-bearing compound such that metal within the metal-bearing compound is reduced to one or more metals while a salt of said reagent is produced; and subsequently regenerating the reducing reagent from the salt. In some embodiments, regenerating the reducing reagent comprises performing thermal, electrochemical, thermochemical, photochemical, and / or mechano-chemical decomposition of the salt. In certain embodiments, regenerating the reducing reagent comprises performing electrochemical decomposition of the salt. In some embodiments, the metal-bearing compound comprises a metal salt. In certain embodiments, the metal-bearing compound comprises a metal oxide, a metal chalcogenide, a metal sulfide, a metal halide, a metal chloride, a metal hydroxide, a metal carbonate, a metal sulfate, a metal carbide, and / or a metal nitride. In some embodiments, the reagent comprises a metallic metal. In certain embodiments, the metallic metal is an alkali metal. In certain embodiments, the alkali metal is lithium, sodium, or potassium. In some embodiments, the alkali metal is sodium. In certain embodiments, the metal-bearing compound comprises copper sulfide. In certain embodiments, the metal-bearing compound comprises copper iron sulfide (e.g., chalcopyrite). In some embodiments, the reducing agent is sodium.

[0009] Certain embodiments relate to systems. In some embodiments, the system comprises an alkali metal fuel cell and an electrochemical cell; wherein the alkali metal fuel cell comprises: a cathode comprising a cathodic reactant comprising gaseous oxygen, gaseous water, and / or gaseous carbon dioxide; and an anode comprising an anodic reactant comprising an alkali metal; and wherein the electrochemical cell comprises: a first electrode comprising electrode active material comprising metallic alkali metal; a second electrode comprising an alkali metalcontaining material; and a solid electrolyte that conducts alkali metal ions in electrochemical communication with the first electrode and the second electrode; wherein the electrochemical cell is configured to produce a metallic metal, wherein: the electrochemical cell is configured such that the alkali metal-containing material is supplied from a source external to the electrochemical cell and / or the electrochemical cell is configured such that the produced metallic metal can be removed from the electrochemical cell.

[0010] Certain embodiments relate to methods. In some embodiments, the method comprises receiving a metallic metal from a location that is remote from a primary site; and oxidizing the metallic metal to produce oxidized product and energy at the primary site; wherein oxidizing comprises discharging an alkali metal fuel cell to produce an electric current; wherein the alkali

[0011] #14431536vl metal fuel cell comprises: a cathode comprising a cathodic reactant comprising gaseous oxygen, gaseous water, and / or gaseous carbon dioxide; and an anode comprising an anodic reactant comprising the metallic metal.

[0012] Other advantages and novel features of the present disclosure will become apparent from the following detailed description of various non-limiting embodiments of the disclosure when considered in conjunction with the accompanying figures. In cases where the present specification and a document incorporated by reference include conflicting and / or inconsistent disclosure, the present specification shall control.

[0013] BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Non-limiting embodiments of the present disclosure will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale unless otherwise indicated. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the disclosure shown where illustration is not necessary to allow those of ordinary skill in the art to understand the disclosure. In the figures:

[0015] FIGS. 1A-1B are schematic diagrams of systems for reducing a metal-bearing compound, in accordance with certain embodiments.

[0016] FIG. 2 is a Na-S phase diagram.

[0017] FIG. 3 is a schematic diagram of an integrated system comprising chemical and electrochemical reactors and subsystems for transporting copper sulfide bearing feedstock into, metal and sulfur products from, and sodium sulfide intermediate product within said system, in accordance with certain embodiments. Not shown is a subsystem for removing sulfur as a solid or liquid from Na-S containing electrochemical reaction chamber.

[0018] FIG. 4A is a schematic diagram of an electrochemical cell for sodium production using sodium sulfide or poly sulfide feedstock, in accordance with certain embodiments.

[0019] FIG. 4B is a schematic diagram of an electrochemical cell for sodium production using sodium hydroxide feedstock, in accordance with certain embodiments.

[0020] FIG. 5 is a Na-Cu-S ternary phase diagram at 25 °C. The target composition for the reaction: CuS (s) + 3 Na (1) — Cu (s) + Na2S (s) + Na (s) is plotted on the phase diagram. Na,

[0021] #14431536vl Cu, and Na2S are highlighted as the three coexisting phases in the region where the target composition resides.

[0022] FIG. 6 is the X-ray diffraction (XRD) spectrum of the products formed from the reaction of CuS and Na. Peaks attributed to Cu, Na2S and Na, the three main phases formed, are labeled.

[0023] FIG. 7 includes a Na-Cu-S ternary phase diagram and a bar chart, both of which compare the actual and expected product compositions from the CuS and Na reaction.

[0024] FIG. 8 is a Cu Pourbaix diagram.

[0025] FIG. 9 includes an X-ray diffraction (XRD) spectrum and a bar chart that show the composition of the solid Cu product separated from Na2S through aqueous means. Cu, the main phase, has labeled peaks on the XRD spectrum.

[0026] FIG. 10 includes a schematic of and a photograph of the real experimental setup of an electrolytic cell used to electro-refine the Cu mixture separated from Na2S after aqueous separation. The electro-refined Cu, plated onto a graphite rod is also shown.

[0027] FIG. 11 is a Na-Zn-S ternary phase diagram at 25 °C. The target composition for the reaction: ZnS (s) + 2 Na (1) — Zn (s) + Na2S (s) is plotted on the phase diagram. Zn and Na2S are highlighted as the two coexisting phases in the region where the target composition resides.

[0028] FIG. 12 is a Na-Zn binary phase diagram.

[0029] FIG. 13 includes a Na-Zn-S ternary phase diagram and a bar chart, both of which compare the actual and expected product compositions from the ZnS and Na reaction.

[0030] FIG. 14 is the X-ray diffraction (XRD) spectrum of the products formed from the ZnS and Na reaction. Peaks attributed to Zn and Na2S, the two main phases formed, are labeled.

[0031] FIG. 15 is a Zn Pourbaix diagram.

[0032] FIG. 16 includes an X-ray diffraction (XRD) spectrum and a bar chart that show the composition of the solid Zn product separated from Na2S through aqueous means. Zn and ZnO, the two main phases, have labeled peaks on the XRD spectrum.

[0033] FIG. 17 is a Na-W-S ternary phase diagram at 25 °C. The target composition for the reaction: WS2 (s) + 4 Na (1) — > W (s) + 2 Na2S (s) is plotted on the phase diagram. W and Na2S are highlighted as the two coexisting phases in the region where the target composition resides.

[0034] FIG. 18 includes a Na-W-S ternary phase diagram and a bar chart, both of which compare the actual (treated at 600 °C for six hours) and expected product compositions from the WS2 and Na reaction.

[0035] #14431536vl FIG. 19 includes a Na-W-S ternary phase diagram and a bar chart, both of which compare the composition of the product after treatment at 600 °C for six hours with the product immediately after the exotherm near 180 °C from the WS2 and Na reaction.

[0036] FIG. 20 is an X-ray diffraction (XRD) spectrum that compares the composition of the product after treatment at 600 °C for six hours with the product immediately after the exotherm near 180 °C from the WS2 and Na reaction. W and Na2S, the two main phases in both products, have labeled peaks on the XRD spectrum.

[0037] FIG. 21 is a W Pourbaix diagram.

[0038] FIG. 22 includes an X-ray diffraction (XRD) spectrum and a bar chart that shows the composition (after treatment at 600 °C for six hours) of the solid W product separated from Na2S through aqueous means. W, the main phase, has labeled peaks on the XRD spectrum.

[0039] FIG. 23 is a plot of expected moles of products formed vs. temperature for the reaction 6 Na (1) + CaW04 (s). The green region captures the temperature range (below 640 °C), in which the desired products - W, Na2O, and CaO - are thermodynamically favorable to form.

[0040] FIG. 24A is a comparison of the XRD spectra and product compositions after sodium reduction of CaW04 and the composition after aqueous separation.

[0041] FIG. 24B is a comparison of the XRD spectra and product compositions after sodium reduction of CaWO4 with CaCh addition and the composition after aqueous separation.

[0042] FIG. 24C includes an XRD spectrum and an expected vs. actual product compositions after sodium reduction of CaWO4 and Fe2O3 with CaCh addition.

[0043] FIG. 24D includes a Na-Sb-S ternary phase diagram with the target and actual compositions of a sodium reduction of Sb2S3 experiment plotted on the diagram. A bar chart comparing the expected vs. actual product compositions of the sodium reduction is also present.

[0044] FIG. 24E is a plot comparing the XRD spectra of the post-reduction and post-aqueous separation products from the Sb2S3 experiment to show purely Sb present after separation.

[0045] FIG. 25 shows an experimental apparatus for demonstrating the design and function of an electrolytic reactor for producing sodium metal from NaOH or aqueous NaOH solutions, incorporating a solid electrolyte, in accordance with certain embodiments.

[0046] FIG. 26A is a plot of current density vs. voltage showing a linear sweep voltammetry scan from NaOH- splitting in an electrolytic reactor, in accordance with some embodiments.

[0047] FIG. 26B includes plots of voltage and current density as functions of time, showing constant current density operation of an electrolytic reactor in which the value of current density

[0048] #14431536vl is stepped from 25 mA / cm2to 500 mA / cm2in increments of 25 mA / cm2, in accordance with some embodiments.

[0049] FIG. 27 shows results for a NaOH- splitting electrolyzer operating at 110°C with 30:70 NaOH:water solution and 130°C with 50:50 NaOH:water solution, compared to a typical Downs cell for producing Na from NaCl at a temperature of about 580°C, according to some embodiments.

[0050] FIG. 28 is a sodium hydroxide water phase diagram, with shaded region showing preferred composition and temperature field according to some embodiments.

[0051] FIG. 29 is the sodium-air fuel cell system disclosed herein, according to some embodiments.

[0052] FIG. 30 shows the disclosed sodium-air fuel cell system can address close to 80% of all aircraft departures and over 30% of current total jet fuel consumption and its associated emissions, according to some embodiments.

[0053] FIG. 31 is a Ragone plot that shows that the disclosed Na-air cell can reach pulse power density of 3000 W / kg and continuous-discharge energy density of 1500 Wh / kg, while retaining the oxygen onboard just reaches the FOA targets, according to some embodiments.

[0054] FIGs. 32A-32C show a schematic of a cell (FIG. 32A), a lab-scale cell (FIG. 32B); and a Multilayer stack (FIG. 32C), according to some embodiments.

[0055] FIG. 33A shows an intermittent galvanostatic discharge for solid electrolyte Na- Air cell, sputtered gold cathode. FIG. 33B shows Na2O2 discharge product can form under or over the cathode, according to some embodiments. FIG. 33C shows non-limiting embodiments of an oxygen / air electrode.

[0056] FIG. 34A is a configuration of a Downs cell and FIG. 34B is a configuration of a disclosed solid electrolyte cell, according to some embodiments.

[0057] FIG. 35 is a representation of the swappable approach with ground-based Na-metal production, storage, and handling with the reloadable / swappable Na-air cell, according to some embodiments.

[0058] FIGS. 36A-36C demonstrate a fast reaction of Na-air discharge product, according to some embodiments. FIG. 36A shows crystalline NaOH formed immediately upon exposure of NaxOyreacts with ambient water within <2 min losing crystallinity. FIG. 36B shows that after Ih exposure, the discharge product had reacted with ambient CO2 forming Na2CO3’H2O. FIG. 36C shows that Na2CO3’H2O crystals were observed via SEM.

[0059] #14431536vl FIG. 37 A, FIG. 37B, and FIG. 37C are, in accordance with some embodiments, a sodium-gas test cell.

[0060] FIG. 38 is a plot of the voltage versus the throughput for various conditions.

[0061] FIG. 39 shows x-ray diffraction patterns for inlet gas streams of dry O2 vs. 100% humidity O2.

[0062] FIG. 40 shows scanning electron microscope images of the discharge product at different stages of evolution, showing that it is possible to control the morphology of the discharge product by varying humidity, in accordance with some embodiments.

[0063] FIG. 41 shows design principles for an MIEC-based oxygen / air electrode, according to some embodiments.

[0064] FIG. 42 shows cathode materials for sodium-air fuel cells, in accordance with some embodiments.

[0065] FIG. 43 shows a process of making an MIEC cathode and building a cell, in accordance with some embodiments.

[0066] FIG. 44A and FIG. 44B show electrochemical test results for a Na-air fuel cell with an MIEC cathode comprising a composite of Nao.?Mn02 / Super P carbon / PVDF, in accordance with some embodiments.

[0067] FIG. 45 shows SEM images of the top surface of an MIEC electrode before and after discharging.

[0068] FIG. 46A and FIG. 46B show cross-sectional SEM images and elemental maps confirming the formation of a NaxOylayer on the cathode after discharging.

[0069] FIG. 47A and FIG. 47B show Raman spectra confirming Na2CO3 formation in the discharge product after air exposure.

[0070] FIG. 48 shows a cermet design for an MIEC cathode comprising a solid electrolyte phase, in accordance with some embodiments.

[0071] FIG. 49 shows a process for making a cermet electrode, in accordance with some embodiments.

[0072] FIG. 50 shows a process for making a cermet electrode, in accordance with some embodiments.

[0073] FIG. 51A plots the current density versus areal capacity for various lithium and sodium comparators compared to an alkali metal fuel cell in accordance with embodiments disclosed herein. FIG. 5 IB plots the power density versus energy density for various lithium and sodium

[0074] #14431536vl comparators compared to an alkali metal fuel cell in accordance with embodiments disclosed herein.

[0075] FIG. 52A shows a solid state pellet fixture fuel cell and a liquid tray fixture fuel cell, in accordance with some embodiments.

[0076] FIG. 52B shows an H-cell, in accordance with some embodiments.

[0077] FIG. 53A shows GITT discharge data obtained using a sodium cell configuration in accordance with FIG. 52 A.

[0078] FIG. 53B plots cell overpotential, taken as the difference between cell voltage at the end of a galvanostatic segment and the OCV, shown against water activity.

[0079] FIG. 53C and FIG. 53D show FIB cross-section images of sodium cell stacks after discharging 0.98 mAh / cm2(9 pm thick Na metal) in dry oxygen (FIG. 53C) and 26 mAh / cm2(240 pm thick Na metal) in 12% (FIG. 53D).

[0080] FIG. 54A and FIG. 54B are time-series x-ray diffraction plots.

[0081] FIG. 54C plots temperature versus weight percent NaOH (%).

[0082] FIG. 55A plots voltage versus throughput under various conditions. FIG. 55B plots voltage versus current density at various temperatures. FIG. 55C plots DC Area Specific Resistance versus throughput under various conditions. FIG. 55D is a photo of an H-cell design, in accordance with some embodiments.

[0083] FIG. 56 plots the first discharge pulse followed by a rest at varying operating temperatures, while holding the bubbler temperature constant.

[0084] FIG. 57 shows GITT cycling data for two planar cells, one cycled at 1 mA / cm2(cell A) and the other at 2 mA / cm2(cell B).

[0085] FIG. 58A shows an FIB cross-section image of a cell post-mortem after passing 9um of Na for the dry conditions. FIG. 58B shows an FIB cross-section image of a cell post-mortem after passing 250um of Na for the humidified conditions. FIG. 58C plots voltage versus throughput from the dry and humidified conditions of FIGs. 58A and 58B. FIG. 58D shows schematics of the initial, dry, and humidified cells.

[0086] FIGs. 59 A and 59B show the Raman spectra measured during discharge, separated by pulse number as well as the mode (discharge versus rest), where FIG. 59B is zoomed in to 3500- 3700cm’1.

[0087] FIGs. 60A and 60B are planview SEM images of a cell after it has been discharged for 24mAh / cm2with a pulsed discharge of 2mA / cm2, 105’C operation, 50’C bubbler. FIG. 60A

[0088] #14431536vl was taken after the cell had been assembled and exposed to air. The planview image after washing is shown in FIG. 60B. EDS results are shown in FIG. 60C.

[0089] FIG. 61 shows the temperature dependence of the ionic conductivity of Na- / ?” alumina measured with electrochemical impedance spectroscopy.

[0090] FIGs. 62A and 62B show a first discharge pulse followed by rest at varying cell and bubbler temperatures (15 minutes at ImA / cm2followed by a 5 minute rest with a 50nm sputtered gold film cathode). FIG. 62A uses a fixed bubbler temperature of 25 °C. FIG. 62B uses a fixed cell temperature of 100 °C.

[0091] FIGs. 63A and 63B show EDS mapping of FIB cross-sections following discharge in dry (FIG. 63 A) and humidified conditions (FIG. 63B).

[0092] FIG. 64 shows an experimental setup.

[0093] FIG. 65 shows the results of a deliquescence study.

[0094] FIG. 66 plots mass versus time for NaOH.

[0095] FIG. 67 is an alkali metal fuel cell, in accordance with some embodiments.

[0096] FIG. 68 is a system comprising an optional electrochemical cell, an optional alkali metal storage and handling system, and an alkali metal fuel cell, in accordance with some embodiments.

[0097] FIG. 69 shows a liquid tray fixture fuel cell comprising a separator, in accordance with some embodiments.

[0098] FIG. 70 shows an H-cell fuel cell comprising a separator, in accordance with some embodiments.

[0099] FIG. 71 is a schematic of a fuel cell comprising a separator and / or inclined separator, and a drain and / or collection system, in accordance with some embodiments.

[0100] FIG. 72 is a schematic of a Multilayer stack comprising fuel cells wherein one or more of the fuel cells comprise a separator, according to some embodiments.

[0101] FIG. 73A and 73B are schematics of an alkali fuel cell comprising a cathode that is not bonded to the solid electrolyte, in accordance with some embodiments.

[0102] FIG. 74 shows the voltage, current, and power for an alkali metal fuel cell comprising a cathode that is not bonded to the solid electrolyte, in accordance with some embodiments.

[0103] FIG. 75 shows an electrochemical cell for sodium production using sodium sulfide or polysulfide feedstock, in accordance with certain embodiments.

[0104] #14431536vl FIG. 76 shows an electrochemical cell for sodium production using molten sodium hydroxide feedstock, according to some embodiments.

[0105] FIGs. 77A-77D show systems comprising different arrangements of sodium production, sodium oxidation, and sodium reduction subsystems, in accordance with certain embodiments. In FIG. 77A, sodium production and reduction occur in one location where sodium precursor may be abundant, while sodium oxidation occurs in another location where energy demand is high. In FIG. 77B, sodium reduction may occur at a location distinct from sodium production and oxidation, where energy may be inexpensive. In FIG. 77C, the oxidant is transported along with the sodium from the reduction subsystem to the oxidation subsystem. In FIG. 77D, the oxidants for the sodium production and sodium reduction subsystems are used for another purpose or discarded.

[0106] FIG. 78 shows an experimental apparatus for demonstrating design and function of an electrolytic reactor for producing sodium metal from NaOH or aqueous NaOH solutions, incorporating a solid electrolyte, in accordance with certain embodiments.

[0107] FIG. 79 is a plot of current density vs. voltage showing a linear sweep voltammetry scan from NaOH-splitting electrolytic reactor, in accordance with some embodiments.

[0108] FIG. 80 includes plots of voltage and current density as functions of time, showing constant current density operation of an electrolytic reactor in which the value of current density is stepped from 25 mA / cm2to 500 mA / cm2in increments of 25 mA / cm2, in accordance with some embodiments.

[0109] FIG. 81 shows results for an NaOH-splitting electrolyzer operating at 110°C with 30:70 NaOH:water solution and 130°C with 50:50 NaOH:water solution, compared to a Downs cell for producing Na from NaCl at a temperature of about 580°C, according to some embodiments.

[0110] FIG. 82 is a sodium hydroxide water phase diagram, with the shaded region showing preferred composition and temperature field, according to some embodiments.

[0111] FIG. 83 is a schematic detailing the use of sodium as an energy carrier, in accordance with some embodiments. In this schematic, sodium is produced via electrolysis in areas with low cost of electricity and low demand for energy and shipped to areas with high cost of electricity and high demand for energy, where it is consumed in a fuel cell to produce energy. In this schematic, the discharge product, sodium hydroxide, is shipped back for electrolysis, thereby closing the loop.

[0112] #14431536vl FIGs. 84A-84B show an electrolysis cell H-cell configuration using liquid sodium as the cathode current collector, in accordance with some embodiments. FIG. 84A shows an exploded view while FIG. 84B shows a photograph of the cell.

[0113] FIGs. 85A-85C show electrical test results for Cells 1 and 2, electrolysis of 50 wt % aqueous sodium hydroxide at 110°C and 130°C respectively (build and test parameters described in Table 4). FIG. 85A shows LSV from OCV to 7 V with a scan rate of 10 mV / s. FIG. 85B shows GITT current density ladder for Cell 1 with 30 minute pulses, a starting current density of 40 mA / cm2, and increments of 40 mA / cm2. FIG. 85C shows GITT current density ladder for Cell 2 with 30 minute pulses, a starting current density of 25 mA / cm2, and increments of 25 mA / cm2.

[0114] FIGs. 86A-86B show an electrolysis cell H-cell configuration using mineral oil as a protective fluid in the cathode chamber, in accordance with some embodiments. FIG. 86A shows an exploded view while FIG. 86B shows a photograph of the cell. Spheres of reduced sodium were observed in the cathode chamber.

[0115] FIGs. 87A-87B show electrical test results for Cell 3, electrolysis of 50 wt % aqueous sodium hydroxide at 120 °C (build and test parameters described in Table 4). FIG. 87A shows LSV from OCV to 5 V with a scan rate of 10 mV / s. FIG. 87B shows GITT with 15 minute, 40 mA / cm2pulses, and 5 minute rests.

[0116] FIGs. 88A-88B show electrical test results for Cell 4, electrolysis of 50 wt % aqueous sodium sulfide at 120°C (build and test parameters described in Table 4). FIG. 88A shows LSV from OCV to 6 V with a scan rate of 10 mV / s. FIG. 88B shows GITT with 15 minute, 160 mA / cm2pulses, and 5 minute rests.

[0117] FIG. 89 shows performance metrics for all electrolysis cells tested. LSV data is shown with lines and GITT data with points. Each GITT point represents the last voltage in a 30 minute galvanostatic charge pulse in order to capture any time-dependent overpotentials. Operating conditions for the Castner process and Downs cell are shown by the diamond markers. The Castner process operating condition includes a 0.4 faradaic efficiency.

[0118] FIG. 90A shows a system comprising an alkali metal fuel cell and an electrochemical cell, wherein the alkali metal fuel cell comprises an anode and cathode, and the electrochemical cell comprises a first electrode, a second electrode, and a solid electrolyte, in accordance with some embodiments.

[0119] #14431536vl FIG. 90B shows a system comprising an alkali metal fuel cell and an electrochemical cell, wherein the alkali metal fuel cell comprises an anode, a cathode, and an optional solid electrolyte, and the electrochemical cell comprises a first electrode, a second electrode, and a solid electrolyte, in accordance with some embodiments.

[0120] DETAILED DESCRIPTION

[0121] Sustainable mining and extraction of metals from naturally occurring ores is a critical industrial and societal need. Processes which avoid or minimize the use of fossil fuels, have low energy consumption, minimize waste such as tailings, and pollutants such as acid (or alkaline) runoff, fine particulate matter, and gaseous emissions including but not limited to carbon dioxide, methane, nitrous oxides, sulfur oxides, and hydrogen sulfide are desired.

[0122] Certain embodiments described in this disclosure comprise methods and systems for extracting metals from metal-bearing compounds. Certain embodiments comprise the use of one or more reagents which reduce a metal bearing compound to one or more metals, while producing a salt of said reagent from which said reagent is subsequently regenerated. The one or more metals produced by this method may comprise a pure metallic metal, a mixture of metallic metals, and / or a mixture of one or more metallic metals with one or more other components, such as one or more metal oxides and / or metal sulfides. In some embodiments, the reagent is a reducing reagent. Regeneration of said reagent allows the process loop to be closed, such that a majority of said reagent may be reused, in accordance with some embodiments.

[0123] In some embodiments, said reagent is regenerated from said salt of the reagent using a process that comprises thermal, thermochemical, photochemical, electrochemical, or mechanochemical decomposition of said salt.

[0124] In some embodiments, said reagent is regenerated from said salt of the reagent using a process that comprises an electrochemical reaction which decomposes said salt. For example, the electrochemical reaction may be an electrochemical decomposition. In some embodiments, the electrochemical decomposition is performed in an electrochemical cell. For example, as described in greater detail elsewhere herein, the electrochemical decomposition may be performed in an electrochemical cell in which the reagent and the salt each comprise an electrode of the electrochemical cell.

[0125] As described in greater detail elsewhere herein, a method as described above may be performed in a system, For example, as shown in FIG. 1A, system 100 comprises reduction

[0126] #14431536vl subsystem 101, in which a metal bearing compound is contacted with a reducing reagent to form salt of the reagent 201 and produced metal 202. Salt of the reducing reagent 201 may be decomposed in decomposition subsystem 102 to form reducing reagent 203. At least a portion of reducing reagent 203 may be transported to reduction subsystem 101 to be contacted with a metal bearing compound. As described in greater detail elsewhere herein, the system may comprise one or more additional components and / or subsystems. For example, as shown in FIG. IB, system 150 comprises all of the components of system 100 shown in FIG. 1A, as well as purification subsystem 103, in which produced metal 202 is purified to produce purified metal 204.

[0127] In some embodiments, the feedstock for said mining or extraction process comprises a metal salt, including but not limited to metal oxides, metal chalcogenides, metal sulfides, metal halides, metal chlorides, metal hydroxides, metal carbonates, metal sulfates, metal carbides, or metal nitrides. Such feedstocks can be used as metal-bearing compounds, in accordance with certain embodiments. Said feedstock may comprise a naturally occurring ore, a concentrate produced from a naturally occurring ore, a tailing from a mining or extraction process, a waste or residue of a chemical or manufacturing process, or a component of a product undergoing recycling. In some embodiments the process is used to recycle materials or components of a manufactured product, or manufacturing scrap.

[0128] In some embodiments, said reagent comprises a metal. In certain embodiments that may be particularly advantageous, said reagent is an alkali or alkaline earth metal. In embodiments that may be still further advantageous, said reagent comprises lithium, sodium, potassium, calcium, or magnesium metal.

[0129] In some embodiments, said alkali or alkaline earth metal reagent is used to reduce the metal-bearing compound (e.g., a metal-bearing compound provided as a feedstock) to produce one or more metals, also forming an alkali or alkaline earth metal salt. In some embodiments, the alkali or alkaline earth metal salt is subsequently allowed to react with carbon dioxide. In some embodiments, the source of carbon dioxide is atmospheric carbon dioxide.

[0130] In some embodiments, said reducing reagent comprises an alkali metal reagent. The alkali metal reagent may be used to reduce said metal-bearing compound (e.g., a feedstock) to produce one or more metals, forming an alkali metal salt which is subsequently reduced to regenerate said alkali metal using a thermal, thermochemical, photochemical, mechanochemical, or electrochemical process. For example, the alkali metal reducing reagent may be

[0131] #14431536vl used to reduce a metal-bearing compound to form a metal and a salt of the alkali metal reducing reagent. The alkali metal reducing reagent may be regenerated from the salt of the alkali metal reducing reagent by an electrochemical process, such as an electrochemical process performed in an electrochemical cell in which the salt of the alkali metal and the alkali metal are each an electrode of the electrochemical cell, as described in greater detail below.

[0132] Many thermochemical and carbothermic reduction processes are known in the field of extractive metallurgy. Thermochemical processes, in general, suffer from the need for heating, which incur undesirable costs and greenhouse gas emissions from the use of fossil fuels that have typically been the lowest-cost form of thermal energy. Carbothermic reduction processes use carbon as a reducing agent, and have the disadvantage that greenhouse gases, especially carbon dioxide, are produced when the ore or feedstock is reduced to form the metal or metal compound. Amongst the objectives of certain embodiments of the present disclosure are to provide for extractive metallurgy with lower energy input, including carrying out extraction processes at lower temperatures than allowed by previous methods, lower waste production, including fewer or more benign tailings and / or decreased emission of gaseous waste including greenhouse gases, capturing greenhouse gases including carbon dioxide with the waste, residue, and / or tailings of an extraction process, reducing the use of consumable materials, including water, and circularity, which may include the regeneration and reuse of reagents used to carry out various extraction processes.

[0133] Accordingly, certain embodiments comprise materials, devices, methods, and / or systems for the reactive separation of metals and metal-bearing compounds from ores and purified feedstocks (also known as concentrates). Some embodiments comprise materials, devices, methods, and / or systems for the reactive separation of metals from metal-bearing compounds. The metal-bearing compounds may comprise, be part of, and / or may be derived from an ore and / or a concentrate. In some embodiments, the separation of metals from the metal-bearing compounds may be achieved by initiating contact between the metal-bearing compound and a metal (and in certain cases advantageously an alkali metal, and in certain cases still more advantageously lithium, sodium, or potassium metal, or in certain cases advantageously an alkaline earth metal and still more advantageously calcium or magnesium metal) as a reductant (also referred to as a reducing agent or reducing reagent). Said ores and concentrates may comprise one or more compounds from the families comprising metal oxides, metal chalcogenides, or metal halides. A metal-bearing compound, such as a metal-bearing compound

[0134] #14431536vl contained within an ore and / or a concentrate, may comprise one or more compounds from the families comprising metal oxides, metal chalcogenides, metal halides, metal chlorides, metal hydroxides, metal carbonates, metal sulfates, and / or metal carbides. In some embodiments, said metal-bearing compounds, ores, and / or concentrates are reacted with said alkali metal in a displacement reaction wherein said metal oxide, metal chalcogenide, metal halide, metal chlorides, metal hydroxides, metal carbonates, metal sulfates, and / or metal carbides is reduced (e.g., including to the metallic form) while said alkali metal is oxidized (e.g., to an alkali metal salt, including to one or more compounds from the families comprising alkali metal oxides, chalcogenides, halides, chlorides, hydroxides, carbonates, sulfates, and / or carbides (such materials referred to herein as alkali metal salts)).

[0135] In some embodiments, said metal-bearing compounds, ores, and / or concentrates are reacted with said alkaline earth metal in a displacement reaction wherein said metal oxide, metal chalcogenide, metal halide, metal chlorides, metal hydroxides, metal carbonates, metal sulfates, and / or metal carbides is reduced (e.g., including to the metallic form) while said alkaline earth metal is oxidized (e.g., to an alkaline earth metal salt, including to one or more compounds from the families comprising alkaline earth metal oxides, chalcogenides, halides, chlorides, hydroxides, carbonates, sulfates, and / or carbides (such materials referred to herein as alkaline earth metal salts)).

[0136] In certain embodiments, said alkali metal salts and / or alkaline earth metal salts may be separated from said reduced metal-bearing ore or concentrate, and are subsequently treated. Said treatments may comprise disposal, for example, if the waste product is relatively benign, or may comprise utilization of said waste product as a useful product in an application or end market. Such utilization may include the use of the waste product to capture or sequester carbon dioxide from the atmosphere. In other embodiments, said treatments may comprise oxidation or reduction of the alkali metal salt or salts. In one embodiment that can be particularly advantageous, said treatment comprises reduction of one or more of said alkali metal salts using a thermochemical or electrochemical reaction. In some embodiments that are particularly advantageous, at least a portion of said alkali metal salt is reduced to produce alkali metal, which may be reused as the reductant, thereby closing the process loop and resupplying at least a portion of the reductant. In some embodiments, multiple alkali metal salts are produced, one or more of which may be reduced to produce alkali metal while others are treated separately. For example, said alkali metal may comprise an alkali metal sulfide that is electrochemically

[0137] #14431536vl reduced to produce alkali metal and elemental sulfur, along with an alkali metal oxide that is separated and disposed of.

[0138] In some embodiments that are particularly advantageous, at least a portion of said alkaline earth metal salt is reduced to produce alkaline earth metal, which may be reused as the reductant, thereby closing the process loop and resupplying at least a portion of the reductant. In some embodiments, multiple alkaline earth metal salts are produced, one or more of which may be reduced to produce alkaline earth metal while others are treated separately. For example, said alkaline earth metal may comprise an alkali metal sulfide that is electrochemically reduced to produce alkaline earth metal and elemental sulfur, along with an alkaline earth metal oxide that is separated and disposed of.

[0139] Certain of the materials, processes, devices, and systems of the present disclosure may be illustrated using the following example. In the following example, the extraction of copper from copper-bearing compounds is described. However, the same methods can be used to extract other metals from metal-bearing compounds, as discussed below. Copper is a valuable metal, widely used as an electrical conductor in all manner of electrical and electrochemical devices including electronic devices, electrical machinery, batteries, motors, generators, power conversion devices, wiring, transmission lines, and the like. The growing use of low-cost renewable electricity as an energy source is creating greater demand for copper. A widely used source of copper today is chalcopyrite, a copper-iron sulfide mineral which in its pure and stoichiometric form has formula CuFeS2, from which metallic copper and iron are extracted by smelting, a high temperature and energy-intensive process which generates undesirable pollutants if not carefully managed. A barrier to increasing the global production of copper is the social, community, and government regulatory resistance to deployment of new smelting facilities.

[0140] The methods described herein may be used to extract a metal from a metal-bearing compound using a reducing reagent. The methods, according to certain embodiments, may be used to extract copper from copper sulfide bearing ores and / or copper sulfide-containing metalbearing compounds by carrying out a displacement reaction wherein said copper sulfide is reduced to copper metal by an alkali metal such as sodium, forming metallic copper while sodium is oxidized to sodium sulfide, here illustrated for CuS, covellite, as the copper sulfide:

[0141] CuS (solid) + 2Na (liquid) Cu (solid) + Na2S (solid) (Eq. 1)

[0142] #14431536vl This may be a relatively low temperature reaction carried out above the melting point of Na metal (98 °C) for improved reaction kinetics, but below the melting point of the three compounds, CuS, Cu, and Na2S indicated as solids in Eq. 1. The relatively low temperature of the reaction may advantageously reduce the energy required to maintain appropriate reaction temperatures relative to, for example, metallothermic reduction reactions. This reaction is spontaneous, meaning it is energetically downhill in the forward direction, and requires little or no energy input, given that the reaction in Eq. 1 is highly exothermic. The dense Cu phase may be separated from the less dense Na2S by methods including but not limited to flotation or sedimentation or centrifugation. Sulfur may be added to the mixture of Cu and Na2S in order to produce a low-melting liquid phase that facilitates separation.

[0143] In some embodiments, it may be advantageous to use a relatively low amount of a reducing reagent. For example, it may be advantageous to initiate contact between a relatively low amount of the reducing reagent and the metal-bearing compound and / or to carry out such an initiation at a relatively low temperature. For example, again turning to the reaction of a copper- bearing compound such as copper sulfide with a reducing reagent comprising an alkali metal such as sodium, in such a process, it may be advantageous to use a relatively low amount of sodium metal to carry out said displacement reactions and / or to carry out the reaction at a relatively low temperature. Both objectives may be accomplished by using a limited amount of sodium metal, for example by selecting an appropriate ratio of the metal sulfide feedstock to sodium metal, adding additional sulfur, or both, in order to achieve a Na:S ratio lower than 2:1. Thus, more generally, the reaction in Equation 1 may be written: xCuS + j’Na = xCu + NaiS (Eq. 2)

[0144] In some embodiments, the Na:S ratio and temperature are selected so that there is a sodium sulfide liquid phase present during all or a portion of the reaction between the metal sulfide and sodium metal. Without being bound by any particular scientific interpretation, having such a liquid present may improve the rate and homogeneity of the decomposition reaction. The Na-S binary phase diagram, shown in FIG. 2, shows that liquids with lower sodium concentration than Na2S and melting points in the range of about 235°C to 300°C are achievable for this purpose for Na:S ratios between about 1 and about zero. According to some embodiments, the Na-S composition co-existing with the metal sulfide and the metal may comprise mostly or all liquid phase, or may be a mixture of two liquid phase compositions, or

[0145] #14431536vl may be a mixture of an Na-S liquid and an Na-S solid phase. In some embodiments, the atomic ratio of Na:S can be lower than 2: 1.

[0146] Analogous reactions to Equations 1 and 2 apply to other copper-bearing sulfides, including chalcocite, CU2S, digenite, CU9S5, and chalcopyrite, CuFeS2. When one or more other metals are present, said other metal may remain in sulfide form, or may also undergo reduction, depending on the metal and whether reduction is thermodynamically possible and whether the kinetics of the reduction reaction are sufficiently rapid. Taking chalcopyrite as a non-limiting example, a similar reduction reaction to that for copper may occur with the iron sulfide component of the ore or concentrate: xFcS + yNa = xFc + NaiS (Eq. 3)

[0147] A reaction of chalcopyrite with sodium metal may produce a mixture of metallic iron, metallic copper, and sodium sulfide. Separation of such a mixture may be carried out by various methods, non-limiting examples being separation by filtration of solid iron and solid copper from sodium sulfide liquid, magnetic separation of metallic iron from copper and / or sodium sulfide, or density-based separation of copper and / or iron from sodium sulfide. Unreacted chalcopyrite or pyrrhotite (FeS) may also be magnetically separated.

[0148] In addition to copper sulfide and iron sulfide, the feedstock materials and processes, in accordance with certain embodiments, include other metal sulfides which may be reduced to their metal while forming an alkaline sulfide. Metals sulfides that may be reduced by sodium metal and which may therefore be processed by the methods of the invention include, but are not limited to sulfides of silver (Ag), arsenic (As), bismuth (Bi), cadmium (Cd), cobalt (Co), copper (Cu), iron (Fe), gallium (Ga), germanium (Ge), mercury (Hg), indium (In), molybdenum (Mo), nickel (Ni), lead (Pb), palladium (Pd), platinum (Pt), ruthenium (Ru), antimony (Sb), tungsten (W), and zinc (Zn). Examples of such sulfides include, but are not limited to, the sulfides of silver (e.g., Ag2S), arsenic (e.g., AsS), iron (e.g., FeS, FeS2), mercury (e.g., HgS), molybdenum (e.g., M0S2), nickel (e.g., NiS), lead (e.g., PbS), antimony (e.g., Sb2S3), tungsten (e.g., WS2), and zinc (e.g., ZnS). Mixed- metal sulfides such as chalcopyrite (CuFeS2), bornite (CusFeS4), pentlandite (Fe,Ni)9Ss), cobaltite ((Co,Fe)AsS), tetrahedrite (Cui2Sb4Si3) and tennantite (CU12AS4S13) can also be used, in pure or impure forms, including mixtures and solid solutions of two or more metal sulfides.

[0149] In addition to metal sulfide feedstock materials, metals whose oxides may be reduced by sodium metal and which may therefore be processed by the methods of the invention include but

[0150] #14431536vl are not limited to cadmium (Cd), cobalt (Co), chromium (Cr), cesium (Cs), iron (Fe), gallium (Ga), germanium (Ge), manganese (Mn), niobium (Nb), rubidium (Rb), rhodium (Rh), tin (Sn), vanadium (V), tungsten (W). Examples of such oxides include, but are not limited to, the oxides of cobalt (e.g., CoO), chromium (e.g., C Ch , iron (e.g., Fe2O3, Fe3O4), germanium (e.g., GeO2), manganese (e.g., Mn02), and tungsten (e.g., WO3). Mixed-metal oxides such as scheelite (CaW04), wolframite ((Fe, Mn)W04), cobalt ferrite (CoFe2O4), chromite (FeCr2O4), and zinc germanate (Zn2GeO4) can also be used, in pure or impure forms, including mixtures and solid solutions of two or more metal oxides.

[0151] Such metal sulfides and / or metal oxides may occur in one or more crystal structure types and each may accordingly have distinct mineral names (e.g., FeS2 may occur as pyrite or marcasite). Thus, any metal sulfide and / or metal oxide comprising one or more metals for which the free energy of sulfidation and / or oxidation, respectively, is less negative than the free energy of sulfidation and / or oxidation for one or more alkali metals and / or alkaline earth metals (e.g., Li, Na, K, Ca, Mg) under imposed reaction conditions (e.g., at a temperature, a pressure, a gaseous atmosphere, etc.) may be used, in accordance with certain embodiments. Minerals or ores from which metals may be extracted by the methods of the invention comprise one or more of such metals, and may comprise one or more anions, including but not limited to oxygen, sulfur, a chalcogen, or a halogen. The anion may also comprise a polyanion, including but not limited to sulfate, phosphate, chlorate, carbonates, oxalate, and the like.

[0152] In another embodiment, any of the metal salts, minerals, or ores listed above may be reduced by calcium metal, wherein the calcium metal is produced by a reaction of a calcium salt with sodium metal. An example of such a spontaneous reaction is: 2 Na + CaC12 Ca + 2 NaCl. Such calcium metal producing reactions may be conducted concurrently with a metalproducing reaction by incorporating said calcium salt into the reacting mixture. Alternatively, said calcium metal may be produced by such reaction conducted separately, and said calcium metal mixed with the metal salt, mineral, or ore to perform reduction, resulting in a metal.

[0153] In some embodiments, the metal formed when the metal-bearing compound is exposed to the reducing reagent comprises the metal species contained within the metal-bearing compound. In some embodiments, the metal is metallic metal. For example, in embodiments in which the metal-bearing compound comprises a sulfide of silver (Ag), arsenic (As), bismuth (Bi), cadmium (Cd), cobalt (Co), copper (Cu), iron (Fe), gallium (Ga), germanium (Ge), mercury (Hg), indium (In), molybdenum (Mo), nickel (Ni), lead (Pb), palladium (Pd), platinum (Pt), ruthenium (Ru),

[0154] #14431536vl antimony (Sb), tungsten (W), and / or zinc (Zn), the metal may comprise any one of or any combination of metallic silver (Ag), arsenic (As), bismuth (Bi), cadmium (Cd), cobalt (Co), copper (Cu), iron (Fe), gallium (Ga), germanium (Ge), mercury (Hg), indium (In), molybdenum (Mo), nickel (Ni), lead (Pb), palladium (Pd), platinum (Pt), ruthenium (Ru), antimony (Sb), tungsten (W), and / or zinc (Zn). In some embodiments in which the metal-bearing compound comprises an oxide cadmium (Cd), cobalt (Co), chromium (Cr), cesium (Cs), iron (Fe), gallium (Ga), germanium (Ge), manganese (Mn), niobium (Nb), rubidium (Rb), rhodium (Rh), tin (Sn), vanadium (V), and / or tungsten (W), the metal comprises any one of or any combination of metallic cadmium (Cd), cobalt (Co), chromium (Cr), cesium (Cs), iron (Fe), gallium (Ga), germanium (Ge), manganese (Mn), niobium (Nb), rubidium (Rb), rhodium (Rh), tin (Sn), vanadium (V), and / or tungsten (W).

[0155] In some embodiments in which the metal-bearing compound comprises two or more types of metals, the metal comprises a mixture, a solid solution, and / or an alloy of the metals contained within the metal-bearing compound. For example, in some embodiments in which the metal-bearing compound comprises a mixed-metal sulfide, the produced metal comprises a mixture, a solid solution, and / or an alloy of the metals contained within the mixed-metal sulfide. For example, if the metal-bearing compound comprises chalcopyrite (CuFeS2) and / or bornite (CusFeS4), the produced metal may comprise a mixture, a solid solution, and / or an alloy of copper and iron. In some embodiments in which the metal-bearing compound comprises pentlandite (Fe,Ni)9Ss), the produced metal comprises a mixture, a solid solution, and / or an alloy of iron and nickel. In some embodiments in which the metal-bearing compound comprises cobaltite ((Co,Fe)AsS), the produced metal may comprise a mixture, a solid solution, and / or an alloy of cobalt and iron. In some embodiments in which the metal-bearing compound comprises tetrahedrite (Cui2Sb4Si3), the produced metal comprises a mixture, a solid solution, and / or an alloy comprising copper and antimony. In some embodiments in which the metalbearing compound comprises tennantite (CU12AS4S13), the produced metal comprises copper and arsenic.

[0156] The method described herein may comprise purifying the produced metal (e.g., to a purity of at least 90 at%, at least 95 at%, at least 99 at%, at least 99.9 at%, at least 99.99 at%, at least 99.999 at%, or up to 100 at%, other than unavoidable impurities). In some embodiments, the purifying comprises electrolytic purifying. For example, the method may comprise electrorefining and / or electrowinning of the produced metal.

[0157] #14431536vl In some embodiments, contacting the metal-bearing compound with the reducing reagent results in the formation of a salt of the reducing reagent. The salt of the reducing reagent may be in the form of a solid and / or a liquid. In some embodiments in which the reducing reagent comprises an alkali metal, contacting the metal-bearing compound with the reducing reagent results in the formation of an alkali metal salt. In some embodiments in which the reducing reagent comprises an alkaline earth metal, contacting the metal-bearing compound with the reducing reagent results in the formation of an alkaline earth metal salt. For example, in the embodiment described above in which the metal-bearing compound comprises copper sulfide and the reducing reagent comprises sodium, sodium sulfide may be formed when the copper sulfide is contacted with the sodium. Said sodium sulfide, which may comprise one or more of said solid or liquid compositions, may subsequently be decomposed to liquid or solid sodium metal, Na, and liquid or solid sulfur, S. Continuing with the exemplar wherein said alkali metal is sodium, said sodium sulfide formed as a result of a displacement reaction with said metal sulfide may comprise one or more of said solid or liquid compositions which may subsequently be decomposed to liquid or solid sodium metal (Na), and liquid or solid sulfur (S), using an electrochemical or thermochemical process. As a non-limiting example, the sodium sulfide may be decomposed to Na metal and S as follows:

[0158] Na S xNa + yS (Eq. 4) using an electrochemical cell wherein the negative electrode comprises sodium metal (e.g., liquid sodium metal) and the positive electrode comprises sulfur (e.g., liquid sulfur) and sodium sulfide, and the positive and negative electrodes are separated by a sodium ion conducting solid electrolyte, examples of which include but are not limited to Na-P” -alumina or NaSICON. Such reaction may be carried out, in some embodiments, above the melting points of both Na metal and S. In other embodiments, other temperatures may be employed.

[0159] Such an electrochemical cell is illustrated in FIG. 4A, and may be powered by any source of electricity including renewable electricity. The compound NaxSymay comprise one or more of Na2S, NaS, Na2S4, Na2Ss, or a liquid of composition where x / y is between zero (i.e., pure S) and * (i.e., Na2S). Said electrochemical cell may be operated at a temperature above the melting points of both Na metal and S, such that the products in Eq. 4 are both in the liquid phase, at a temperature between the melting points of Na metal (98°C) and S (113°C), such that the sulfur is solid and the sodium is liquid, or at a temperature below the melting point of Na metal, such that both the sulfur and sodium are solids.

[0160] #14431536vl Again using copper-bearing ores as an example, a system for mining and extraction of copper from chalcopyrite-bearing ores may comprise a subsystem for mining, transporting, crushing, and separating a chalcopyrite concentrate from an ore deposit, a subsystem for reacting said chalcopyrite concentrate with sodium metal, one or more a subsystems for separating reduced copper metal from iron metal, iron sulfide(s), and / or sodium sulfides, a subsystem for electrochemically reducing separated sodium sulfide(s) to sodium metal and elemental sulfur and returning said sodium metal to the subsystem where it is reacted with chalcopyrite concentrate. One or more of said subsystems may be combined. For example, the subsystem for electrochemically reducing sodium sulfide may be integrated with the subsystem wherein sodium metal is reacted with chalcopyrite. Such a combination may have advantages such as reducing transport and possible exposure of sodium metal to air or moisture. FIG. 3 illustrates a non-limiting example of an integrated system comprising a reaction chamber for reacting a feedstock comprising copper sulfide with sodium metal, a subsystem for transporting said feedstock to said reaction chamber, an electrochemical cell for producing said sodium metal from a sodium sulfide source, a subsystem for transporting sodium sulfide formed in said reaction chamber to said electrochemical cell, and a subsystem for transporting metal from said reaction chamber. In this system, sodium is recirculated and reused while said metal sulfide feedstock is reduced to form as products at least one metal and elemental sulfur or sodium sulfide. Said products are conveyed from the system. Referring to FIG. 3, the system may also include a subsystem for removing sulfur as a product from the Na-S chamber of the electrochemical reactor (right hand side). Depending on temperature and composition, said sulfur may be relatively pure elemental sulfur or may be a sulfur-rich sodium sulfide, and may be removed as a liquid or a solid. Sodium used in the process may be replenished as the system operates, as some of said sodium may be reacted with impurities in the feedstock such as oxygen or metals, and may thereby be consumed.

[0161] In some embodiments, one or more parts of the system may operate in the presence of a non-reactive gas. The reaction chamber containing metal sulfide and sodium, the chamber containing sodium sulfide, or transport passageways between parts of the system, may have a gaseous atmosphere that is low in oxygen content and comprises nitrogen, hydrogen, helium, argon, or other gases of low reactivity with sodium metal and / or metal sulfides. The oxygen content of the gaseous atmosphere may have a partial pressure that is less than that of air, less

[0162] #14431536vl than 10% of the total pressure, less than 5% of the total pressure, less than 2% of the total pressure, or less than 1% of the total pressure.

[0163] In some embodiments, one or more parts of the system may operate in the presence of a protective layer of a non-reactive liquid. Chambers containing solid or liquid materials, including but not limited to the reaction chamber containing metal sulfide and sodium or the chamber containing sodium sulfide, may contain a non-reactive liquid such as an oil which has lower density than the solids and other liquids, causing said non-reactive liquid to float on top of and cover or partially cover said solids and other liquids, including solid or liquid sodium metal. Such non-reactive liquids may serve the purpose of preventing contact between reactive solids, including but not limited to sodium metal, metal sulfides, or sodium sulfide, and a reactive gaseous atmosphere.

[0164] Said protective liquid layer may comprise an organic liquid having limited reactivity when in contact with the sodium metal, metal sulfides, or sodium sulfide, and which limits the transport of air or water through the protective liquid. Said sodium metal, metal sulfides, or sodium sulfide may be combined with said protective liquid to provide easier and safer handling, storage, or transference or transport of said materials. The liquid may be hydrophobic or hydrophilic, and may be wetting or non-wetting to the surface of the metal. In a preferred embodiment, the liquid is non-reactive and wetting to the surface of sodium metal, i.e., having a contact angle between the liquid and the metal of 0° to 90°, 5° to 80°, or 10° to 70°. Nonlimiting examples of the liquid include hydrocarbon oils, silicone oils, organic or ionic liquids, polymers, emulsions, gels, suspensions of particles in liquids, or the like.

[0165] In specific embodiments where the metal electrode includes an alkali metal, the liquid may include a hydrophobic compound such as an oil, such as mineral oil or a petroleum-derived hydrocarbon liquid. In an aspect where the metal electrode comprises lithium, sodium, potassium, or an alloy thereof, the protective layer may comprise mineral oil, and may be effective to preclude reaction of the metal electrode with air. Crude petroleum oil has a density of 0.8 to 0.9 g / cm3, silicone oils have densities ranging from 0.74 g / cm3to 1.06 g / cm3, mineral oil and paraffin both have a density of about 0.8 g / cm3, kerosene and diesel fuel have a density of 0.8 g / cm3, and gasoline has a density of 0.74 g / cm3. Solid Na metal has a density of 0.97 g / cm3at room temperature and 0.95 g / cm3at the melting point, and liquid Na metal has a density of 0.93 g / cm3at the melting point to 0.86 g / cm3at 400°C. Thus, there are multiple choices of

[0166] #14431536vl hydrophobic oils having a density less than that of Na, and which will thus provide a protective layer over solid or liquid Na metal, protecting said metal from exposure to atmosphere.

[0167] Certain embodiments include the materials and devices of the subsystems, any combination of said subsystems, a full system, and any method by which each of said subsystems or combination of subsystems, or a full system, operates.

[0168] The systems described herein may comprise a subsystem for purifying the metal (e.g., the metallic metal) produced during the performance of a method described herein. The system(s), according to certain embodiments, may also comprise a subsystem for purifying the metallic copper that is produced. Such a subsystem may comprise an electrolytic process, such as electro winning or electrorefining, wherein a lower-purity copper comprises an anode at which said copper is electrolytically oxidized and dissolved as copper ions in an electrolyte, said copper ions then being electrodeposited (reduced) at a cathode, thereby forming a higher-purity copper. In certain of the system(s) of the present disclosure, said electrolyte may be a sulfuric acid solution, said sulfuric acid being at least in part produced from the sulfur generated by the electrochemical reduction of sodium sulfide. One particular embodiment is the use of feedstock metals for electrorefining in the form of particulate. Such particulates, of metals such as copper, may be produced by the above described methods, in accordance with certain embodiments. In certain embodiments, said particulates are contained within in a vessel or basket wherein metal particulates are in electrical contact with each other and with the current collector of an anode of an electrorefining cell. Said metal particulates may be oxidized at said anode to copper ions which may then be dissolved in the electrolyte of the electrorefiner and electroplated as metal of a higher purity at the cathode of said electrorefiner. Said metal may be in the form of a sheet, foil, rod, or ingot. Said electrorefining subsystem may be employed for improving the purity of any of the above described metals, including but not limited to iron, nickel, lead, zinc, molybdenum, mercury, and arsenic.

[0169] The reactions between a metal sulfide and an alkali metal exemplified by Equations 1-3 may also be carried out for a metal oxide, metal hydroxide, metal carbonate, or other metal salt, resulting in the reduction of the metal salt to a metal or metal alloy and an alkali metal salt comprising an alkaline metal oxide, alkaline metal hydroxide, or alkaline metal carbonate. Said alkaline metal hydroxide may also comprise water, including forming an alkaline metal hydrate or a liquid solution of alkaline metal hydroxide and water. A solution comprising NaOH and water is an example of such a liquid solution. A gaseous product such as hydrogen, water vapor,

[0170] #14431536vl or carbon dioxide may be simultaneously produced as a result of said reactions. In such instances, said alkaline metal salts, their hydrates, and liquid solutions thereof, may be subsequently reduced to one or more alkali metals, including by thermal, thermochemical, or electrochemical methods, allowing said alkali metal thus produced to be re-used in said reduction of said metal salt. As a non-limiting example, consider the reduction of a mineral feedstock comprising a metal oxide MxOyby sodium metal according to the reaction:

[0171] MxOy+ (2y )Na = xM + yNa2O (Eq. 5)

[0172] M may comprise one or more metals for which the free energy of oxidation is less negative than the free energy of oxidation for one or more alkali metals (e.g., Li, Na, K) and / or alkaline earth metals (e.g., Ca, Mg) under imposed reaction conditions (e.g., at a temperature, a pressure, a gaseous atmosphere, etc.). In the instance where the alkali metal is sodium, non-limiting examples of metals for which reaction conditions may be selected wherein the reaction of Eq. 4 may be energetically favorable in the forward direction (e.g., is a spontaneous reaction) include Fe, Ni, Co, Zn, Cu, Ag, and Hg.

[0173] As other non-limiting examples, a metal salt feedstock material, in accordance with certain embodiments, may comprise a metal hydroxide, which may undergo a reaction with sodium of the type:

[0174] AAOH + Na = xM + yNaOH (Eq. 6) wherein said NaOH may be subsequently reduced to sodium metal or decomposed to a sodium oxide which is subsequently reduced to sodium metal, or a metal salt feedstock material, in accordance with certain embodiments, may comprise a metal carbonate, which may undergo a reaction with sodium of the type: CO. ,■ + 2Na = M + Na2CO3(Eq. 7)

[0175] Here, M may include but is not limited to one or more of Ca, Mg, Fe, Mn, Ni, Co, Zn, Cd, Pb, Sr, or Ba.

[0176] The feedstock materials and processes, such as feedstock metal-bearing compounds, in accordance with certain embodiments, may include mixed-metal salts comprising at least one metal (e.g., at least one metal sulfide) such as chalcopyrite (CuFeS2), bornite (CusFeS4), pentlandite (Fe,Ni)9Ss), cobaltite ((Co,Fe)AsS), tetrahedrite (Cui2Sb4Si3) and tennantite (CUI2AS4SI3), in pure or impure forms, including mixtures and solid solutions of two or more metal sulfides. Such metal sulfides may occur in one or more crystal structure types and each may accordingly have distinct mineral names (e.g., FeS2may occur as pyrite or marcasite).

[0177] #14431536vl The alkali metal salt and / or alkaline earth metal salt produced in such reaction may be subsequently reduced to the alkali metal and / or alkaline earth metal therein via a thermochemical reduction, comprising the heating of the alkali metal salt (e.g., sodium salt) and / or alkaline earth metal salt (e.g., calcium salt) in a temperature and gaseous atmosphere wherein the metallic state is thermodynamically preferred over oxidized forms. For example, the sodium oxide produced in such reaction may be subsequently reduced to sodium metal via a thermochemical reduction, comprising the heating of the metal salt (e.g., sodium salt) in a temperature and gaseous atmosphere wherein the metallic state is thermodynamically preferred over oxidized forms. As a non-limiting example in which sodium salt is thermochemically reduced to the metal, sodium oxide, Na2<3, may be heated to a temperature above about 650°C in an atmosphere with oxygen partial pressure less than about 10'8atm, conditions which result in decomposition into sodium and oxygen vapor. The vapor may be cooled in the presence of another compound including but not limited to calcium, silicon, magnesium, or aluminum, which serve as oxygen getters, producing an oxidized version of the getter compound and pure sodium metal.

[0178] Said sodium oxide, or other alkaline metal oxide, may also be combined with water to form one or more alkaline metal hydroxides, hydrates of such alkaline metal hydroxides, and / or liquid solutions of an alkaline metal hydroxide and water. Similarly, any such alkaline earth metal oxide may be combined with water to form one or more alkaline earth metal hydroxides, hydrates of such alkaline earth metal hydroxides, and / or liquid solutions of an alkaline earth metal hydroxide and water. For example, sodium oxide may be combined with water to form NaOH, or NaOH-water solutions. Such hydroxides or their hydrates and solutions may be electrochemically reduced to one or more alkali metals, including in an electrochemical cell in which said sodium hydroxide or its hydrate or aqueous solution thereof is reduced to sodium metal at a cathode, and liquid and / or gas phase species comprising hydrogen and / or oxygen at an anode. One exemplary reaction is the electrochemical decomposition of NaOH according to the reaction:

[0179] 2NaOH 2Na + H2O + * / 2O2(Eq. 8)

[0180] In some embodiments, said electrochemical cells comprise a solid electrolyte which conducts ions of the alkali metal or metals and / or alkaline earth metal or metals used to reduce said metal salt or metal salts comprising a feedstock material, such as a metal-bearing compound. In the case of sodium as the reductant, the solid electrolyte may be a solid sodium ion conductor such

[0181] #14431536vl as one in the general structural and compositional families known as Na-|3” alumina or sodium (Na) super ionic conductor (NaSICON). Solid electrolytes that are used for other alkali ions may be similarly used, including but not limited to K— 13” alumina, LiSICON, or garnet-structure type lithium solid electrolytes such as lithium lanthanum zirconium oxide (LLZO) and its doped derivatives. Advantages to the use of a solid electrolyte may include, in accordance with certain embodiments, a wide electrochemical window affording stability of the solid electrolyte at both highly reducing and highly oxidizing conditions, a high sodium ion conductivity allowing high operating current densities and power densities and decreased overpotentials, and high selectivity for the conducting ion which improves the purity of the electrolytically produced metal and allows for the use of less pure feedstock materials. In addition, use of a solid electrolyte may, in accordance with some embodiments, allow for smaller distances between the cathode and anode. In many traditional processes, if the inter-electrode distance is too small, there is a risk of shorting the cell via the metal that is produced. This risk can be mitigated (e.g., fully mitigated) by the presence of a solid-state electrolyte between the two electrodes. The reduction in distance between the anode and the cathode reduces the overpotential of the cell, in accordance with certain embodiments. Such electrochemical cells may be used with various alkali metal salts produced as a result of the reduction of a metal salt feedstock by an alkali metal. For example, in addition to the use of an electrochemical cell comprising a sodium solid electrolyte for the purpose of sodium production from a feedstock comprising sodium sulfide or sodium polysulfide, as shown in FIG. 4A, an electrochemical cell of similar design may be used to produce sodium metal from feedstocks that comprise sodium hydroxide, including sodium hydrates or mixtures of sodium hydrates including liquid solutions comprising sodium hydroxide, sodium hydrates, or water, as shown in FIG. 4B.

[0182] According to certain embodiments, it is understood that mineral feedstocks are rarely pure, even after beneficiation and separation, and may include multiple metals and metal salts. For example, mixed-metal sulfides, mixed-metal oxides, mixed-metal hydroxide, and mixed- metal carbonates are all well-known. Embodiments can include such metal salts in which one or more metals may be reduced by an alkali metal and one or more may not, or where the reaction conditions may be altered, for example by changing temperature, to reduce one or metals under a first reaction condition, and one or more metals under a second reaction condition. Certain embodiments also comprise the separation and removal of metals or metal alloys produced by reduction with an alkali metal from those which have not been reduced to the metal. In some

[0183] #14431536vl embodiments, unreduced metal salts are separated and discarded, or comprise a separate product with useful applications.

[0184] A metal salt may also comprise more than one anion group, including but not limited to metal salts comprising at least two of the anion groups sulfide, sulfate, oxide, hydroxide, hydrate, carbonate, chloride, halide, or hydride. For example, metal oxysulfides, oxy hydroxides, oxycarbonates, oxychlorides are all known. Metal salts with disparate anion groups may occur as individual crystalline compounds or phases, solid solutions, or mixtures of crystalline compounds or phases. The metal salt feedstocks, in accordance with certain embodiments, include such metal salts. It is understood that reaction with an alkali metal may produce more than one alkali metal salt. Exemplars of non-limiting cases for such alkali metal salts are the product metal salts illustrated in Equations 1, 2, 3, 4, 5, 6 and 7.

[0185] Certain alkali metals are more widely available than others, and accordingly, have lower cost. Certain alkali metal salts also have greater utility and market value than others. In some embodiments, the alkali metal salt produced by reduction of said metal salt is used in another application or market, or has sufficiently low cost or market value that it is discarded. For example, lithium may be used as the alkali metal, and may produce lithium sulfide, lithium hydroxide, or lithium carbonate, each of which may have use in another market. For example, lithium hydroxide and lithium carbonate are both used in producing cathode active materials for lithium ion batteries. As non-limiting examples, lithium hydroxide is a preferred precursor for production of LiCoCE and its derivative compositions, the nickel-cobalt-aluminum oxide family of cathode-active compounds known as “NCA” and the nickel-cobalt-manganese oxide family of cathode-active compounds known as “NCM” or “NMC”. Lithium carbonate is a preferred precursor for producing the lithium metal phosphate family of cathode-active materials, including but not limited to lithium iron phosphate (LFP) and lithium manganese iron phosphate (LMFP). As another example, KOH is a widely used salt in electrolytes for aqueous primary and secondary batteries, and may be produced from the use of potassium metal as a reducing agent for feedstocks which may comprise a metal oxide, metal hydroxide, or metal oxyhydroxide. In certain embodiments, the alkali metal comprises sodium, and the alkali metal salt produced upon reduction of the metal salt feedstock comprises one or more of sodium oxide, sodium hydroxide, sodium hydrate, or sodium carbonate. Sodium is the most abundant of the alkali metals, and said alkali metal salts may be useful in several applications. Sodium hydroxide, NaOH, is widely produced commercially as a base (or caustic), and may be produced

[0186] #14431536vl as a result of the reduction reaction, e.g., Eq. 6, or by the reaction of Na2<D, Eq. 5, or an analogous reaction producing sodium peroxide, Na2<D2, upon the reaction of such sodium oxides with water, e.g.:

[0187] Na2O + H2O = 2NaOH (Eq. 9)

[0188] Upon exposure to carbon dioxide, including atmospheric carbon dioxide or concentrated point sources of carbon dioxide including but not limited to fossil-fuel combustion power plants, engines and turbines, cement kilns, steel furnaces, Haber-Bosch reactors producing ammonia, and direct-air-capture (DAC) plants removing carbon dioxide from the air, NaOH may react with carbon dioxide to form sodium carbonate:

[0189] 2NaOH + CO2= Na2CO3+ H2O (Eq. 10)

[0190] Thus, according to some embodiments, the product of the reduction reaction may be used to capture and / or sequester carbon dioxide, thereby removing carbon dioxide from the atmosphere, or avoiding the release of carbon dioxide into the atmosphere.

[0191] As both sodium hydroxide and sodium carbonate are bases, another use of these reaction products may be the de-acidification of water bodies, including the oceans, or enabling additional carbon capture according to the reaction

[0192] Na2CO3+ CO2+ H2O 2NaHCO3(Eq. 11)

[0193] The methods and systems, in accordance with certain embodiments, can include apparatuses, subsystems, and systems for transporting, distributing, and / or utilizing the alkali metal salts of the reaction for such purposes.

[0194] This disclosure also describes energy storage and delivery systems and related articles and methods. The energy storage and delivery systems and related articles and methods described below can be used in combination with the methods and systems for reactive extraction of metals from metal-bearing compounds described above, in accordance with some embodiments. For example, in some cases, the electrochemical cells and / or alkali metal fuel cells described below can be used in combination with the methods disclosed above or elsewhere herein. In certain embodiments, the alkali metal fuel cells described below may be discharged to provide energy in the form of electric power and / or heat prior to initiating contact between the metal-bearing compound and the reducing agent described above, wherein the provided energy is used in initiating the contact. In some embodiments, the alkali metal fuel cells described below may be discharged to provide energy in the form of electric power and / or heat prior to regenerating the reducing agent, as described above, wherein the provided energy is

[0195] #14431536vl used in regenerating the reducing agent. In some embodiments, the electrochemical cells described below may be used to regenerate the reducing agent from a salt of the reducing agent.

[0196] Herein, the energy storage and delivery systems and related articles and methods are generally described. Certain aspects relate to energy storage and delivery systems that employ metallic sodium and / or metallic lithium and / or metallic potassium as an electrochemically active material. The subject matter of the present disclosure involves, in some cases, interrelated products, alternative solutions to a particular problem, and / or a plurality of different uses of one or more systems and / or articles.

[0197] Certain embodiments relate to systems. In some embodiments, the system comprises an alkali metal fuel cell and an electrochemical cell; wherein the alkali metal fuel cell comprises: a cathode comprising a cathodic reactant comprising gaseous oxygen, gaseous water, and / or gaseous carbon dioxide; and an anode comprising an anodic reactant comprising an alkali metal; and wherein the electrochemical cell comprises: a first electrode comprising electrode active material comprising metallic alkali metal; a second electrode comprising an alkali metalcontaining material; and a solid electrolyte that conducts alkali metal ions in electrochemical communication with the first electrode and the second electrode; wherein the electrochemical cell is configured to produce a metallic metal, wherein: the electrochemical cell is configured such that the alkali metal-containing material is supplied from a source external to the electrochemical cell and / or the electrochemical cell is configured such that the produced metallic metal can be removed from the electrochemical cell.

[0198] Certain embodiments relate to methods. In some embodiments, the method comprises receiving a metallic metal from a location that is remote from a primary site; and oxidizing the metallic metal to produce oxidized product and energy at the primary site; wherein oxidizing comprises discharging an alkali metal fuel cell to produce an electric current; wherein the alkali metal fuel cell comprises: a cathode comprising a cathodic reactant comprising gaseous oxygen, gaseous water, and / or gaseous carbon dioxide; and an anode comprising an anodic reactant comprising the metallic metal.

[0199] This disclosure describes materials, devices, systems, subsystems, and methods of use in which metallic metal (e.g., metallic sodium, such as sodium metal or alloys comprising sodium, metallic lithium, such as lithium metal or alloys comprising lithium, and / or metallic potassium, such as potassium metal or alloys comprising potassium) is employed as an energy carrier. Various embodiments comprise the production of metallic metal (e.g., metallic sodium such as

[0200] #14431536vl sodium metal or alloys comprising sodium, metallic lithium, such as lithium metal or alloys comprising lithium, and / or metallic potassium, such as potassium metal or alloys comprising potassium), chemical or electrochemical oxidation of metallic metal (e.g., sodium and / or lithium and / or potassium) to produce energy (which may comprise heat and / or electricity), and the restoration or conversion of the oxidized metal or metal alloy back to the metallic state so that it may be reused. Operating in this fashion can, thus, “close the loop.” The oxidized form of the metal (e.g., sodium and / or lithium and / or potassium) may comprise a metal salt. Examples of metal salts include, but are not limited to, a metal halide (e.g., a sodium halide and / or a lithium halide and / or a potassium halide), a metal sulfide (e.g., sodium sulfide and / or lithium sulfide and / or potassium sulfide), a metal oxide (e.g., sodium oxide and / or lithium oxide and / or potassium oxide), a metal peroxide (e.g., sodium peroxide and / or lithium peroxide and / or potassium peroxide), a metal hydroxide (e.g., sodium hydroxide and / or lithium hydroxide and / or potassium hydroxide), or a metal hydroxide hydrate (e.g., sodium hydroxide hydrate and / or lithium hydroxide hydrate and / or potassium hydroxide hydrate) in their solid or melt or vapor forms, liquid solutions comprising dissolved forms of one or more of said metal salts, or aqueous solutions comprising dissolved forms of one or more of said metal salts. In some embodiments, said aqueous solution comprises dissolved metal hydroxide (e.g., sodium hydroxide and / or lithium hydroxide and / or potassium hydroxide), or metal carbonate (e.g., sodium carbonate and / or lithium carbonate and / or potassium carbonate), or metal bicarbonate (e.g., sodium bicarbonate and / or lithium bicarbonate and / or potassium bicarbonate). In certain embodiments, said metal salt (e.g., sodium salt and / or lithium salt and / or potassium salt) comprises solid or molten metal sulfide (e.g., sodium sulfide and / or lithium sulfide and / or potassium sulfide), and said solutions comprise aqueous or nonaqueous metal poly sulfide (e.g., sodium poly sulfide and / or lithium polysulfide and / or potassium polysulfide) solutions. Some embodiments comprise the thermochemical and / or electrochemical conversion or reduction of the oxidized metal (e.g., sodium and / or lithium and / or potassium) salt back to the metallic state.

[0201] As used herein, “metallic” metals are metals having an oxidation state of zero. To illustrate, pure sodium metal in a zero oxidation state would be metallic sodium. Sodium that is part of sodium chloride salt, however, would not be metallic sodium because sodium in that form has an oxidation state of +1.

[0202] Metal elements in metallic form are also referred to herein as that element followed by “metal.” For example, metallic sodium is also referred to herein as “sodium metal.”

[0203] #14431536vl It can be particularly advantageous, in some embodiments, to use sodium metal in certain of the embodiments described herein. Sodium has a high crustal abundance on Earth and when present in elemental or metallic form, may be oxidized, producing thermal or electrical energy in various devices. The low cost and high energy density of sodium metal makes it an attractive energy carrier for storage and delivery of energy in various applications, including but not limited to industrial chemical or manufacturing processes, electricity for the power grid, stationary power applications, portable electrical devices, or electric transportation (e.g., twowheeled electric transportation, electric automobiles, electric aviation, electric locomotion, electric trucking, or electric watercraft).

[0204] While various embodiments disclosed herein are described using sodium as the metal element, it should be understood that this disclosure is not so limited, and in other embodiments, other metals could be used, such as lithium metal or potassium metal.

[0205] As used herein, “oxidation” is understood to mean an increase in the oxidation state of a metal. For example, oxidation of sodium can involve changing Na° to Na+1. Oxidation (e.g., of sodium) may occur, for example, through a chemical reaction with chlorine, oxygen, water, carbon dioxide, sulfur, or other species. As used herein, “reduction” is correspondingly understood to mean a decrease in the oxidation state of a metal, including to the metallic state. In certain embodiments, oxidation of sodium or its alloys produces thermal energy. In some embodiments, oxidation of a metallic metal (e.g., sodium and / or lithium and / or potassium) or its alloys to produce thermal energy includes the reaction of the metallic material (e.g., with oxygen or water) in a furnace or reactor comprising a combustion chamber. Some such embodiments comprise transferring heat (e.g., generated via oxidation of the metallic material, such as sodium metal or its alloys and / or lithium metal or its alloys and / or potassium or its alloys) to an end application. In some embodiments, the oxidation of metallic material (e.g., sodium metal or its alloys and / or lithium metal or its alloys and / or potassium or its alloys) produces electrical energy. For example, in some embodiments, the oxidation of metallic metal (e.g., sodium metal or its alloys and / or lithium metal or its alloys and / or potassium or its alloys) is part of the operation of a battery or fuel cell (e.g., a sodium metal-air battery or fuel cell, which can, for example, involve the oxidation of the metal to produce a sodium salt) (e.g., a lithium metal-air battery or fuel cell, which can, for example, involve the oxidation of the metal to produce a lithium salt) (e.g., a potassium metal-air battery or fuel cell, which can, for example, involve the oxidation of the metal to produce a potassium salt). In some embodiments, said metal salt (e.g.,

[0206] #14431536vl sodium salt and / or lithium salt and / or potassium salt) is reduced to the metal. Reduction of the metal salt (e.g., sodium salt and / or lithium salt and / or potassium salt) to the metal can be performed via thermochemical reduction, comprising the heating of the metal salt (e.g., sodium salt and / or lithium salt and / or potassium salt) in a temperature and gaseous atmosphere wherein the metallic state is thermodynamically preferred over oxidized forms.

[0207] Certain embodiments relate to systems. Some non-limiting examples of systems are shown in FIGs. 29, 32C, 35, 68, 72, 83, and 90A-90B. In some embodiments, the system comprises an alkali metal fuel cell (e.g., any alkali metal fuel cell disclosed herein). For example, as shown in FIGs. 90A and 90B, in some cases, system 400 comprises alkali metal fuel cell 401. In certain embodiments, the system comprises an electrochemical cell (e.g., any electrochemical cell disclosed herein). For example, as shown in FIGs. 90A and 90B, in some cases, system 400 comprises electrochemical cell 402. According to some embodiments, the system comprises an alkali metal fuel cell (e.g., any alkali metal fuel cell disclosed herein) and an electrochemical cell (e.g., any electrochemical cell disclosed herein). For example, as shown in FIGs. 90A and 90B, in some cases, system 400 comprises alkali metal fuel cell 401 and electrochemical cell 402.

[0208] In accordance with some embodiments, the electrochemical cell comprises one or more electrodes. For example, in certain cases, the electrochemical cell comprises a first electrode and a second electrode. For example, as shown in FIGs. 90A and 90B, in some cases, electrochemical cell 402 comprises first electrode 405 and second electrode 406.

[0209] According to certain embodiments, the first electrode comprises an electrode active material. In some instances, the electrode active material of the first electrode comprises metallic alkali metal (e.g., metallic sodium and / or metallic lithium and / or metallic potassium). For example, in certain cases, the metallic alkali metal of the electrode active material of the first electrode comprises metallic sodium. As another example, in some cases, the metallic alkali metal of the electrode active material of the first electrode comprises metallic lithium. As another example, in some cases, the metallic alkali metal of the electrode active material of the first electrode comprises metallic potassium. As another example, in some cases, the metallic alkali metal of the electrode active material of the first electrode comprises metallic potassium. In accordance with certain embodiments, the metallic alkali metal (e.g., metallic sodium and / or metallic lithium and / or metallic potassium) of the electrode active material of the first electrode

[0210] #14431536vl is liquid metallic alkali metal (e.g., lithium metallic sodium and / or liquid metallic lithium and / or liquid metallic potassium).

[0211] In accordance with some embodiments, the second electrode comprises an alkali metalcontaining material. In certain instances, the alkali metal-containing material is anhydrous. In some embodiments, the alkali metal-containing material is aqueous. In accordance with certain embodiments, the alkali metal-containing material comprises an alkali metal hydroxide and / or an alkali metal sulfide. It should be understood that an alkali metal hydroxide is not metallic alkali metal and an alkali metal sulfide is not metallic alkali metal.

[0212] According to some embodiments, the alkali metal-containing material comprises an alkali metal hydroxide (e.g., sodium hydroxide and / or lithium hydroxide and / or potassium hydroxide). In some instances, the alkali metal hydroxide of the alkali metal-containing material comprises lithium hydroxide. In certain instances, the lithium hydroxide of the alkali metalcontaining material is in the form of an aqueous lithium hydroxide solution. According to certain embodiments, the alkali metal hydroxide of the alkali metal-containing material comprises sodium hydroxide. In certain instances, the sodium hydroxide of the alkali metalcontaining material is in the form of an aqueous sodium hydroxide solution. According to certain embodiments, the alkali metal hydroxide of the alkali metal-containing material comprises potassium hydroxide. In certain instances, the potassium hydroxide of the alkali metalcontaining material is in the form of an aqueous potassium hydroxide solution.

[0213] According to certain embodiments, the alkali metal-containing material comprises an alkali metal sulfide (e.g., sodium sulfide). In some embodiments, the alkali metal-containing material (e.g., the alkali metal sulfide) comprises sodium sulfide. In certain cases, the sodium sulfide is in the form of an aqueous sodium sulfide solution.

[0214] In accordance with some embodiments, the alkali metal-containing material comprises an alkali metal hydroxide and an alkali metal sulfide. For example, in some cases, the alkali metalcontaining material comprises sodium hydroxide and sodium sulfide. As another example, in some cases, the alkali metal-containing material comprises sodium hydroxide and sodium sulfide in the form of an aqueous solution.

[0215] In accordance with certain embodiments, the second electrode comprises a porous electronically conductive material capable of initiating and / or catalyzing anion oxidation. For example, in some cases, the second electrode comprises a nickel foam. As another example, in

[0216] #14431536vl some cases, the second electrode comprises carbon. In certain embodiments, the second electrode does not conduct ions.

[0217] In certain cases, the electrochemical cell comprises a solid electrolyte. For example, as shown in FIGs. 90A and 90B, in some cases, electrochemical cell 402 comprises solid electrolyte 412. In accordance with some embodiments, the solid electrolyte is in electrochemical communication with the first electrode and the second electrode. In some instances, the solid electrolyte conducts alkali metal ions (e.g., sodium ions and / or lithium ions and / or potassium ions). For example, in certain embodiments, the solid electrolyte conducts sodium ions. As another example, in some embodiments, the solid electrolyte conducts lithium ions. As yet another example, in some embodiments, the solid electrolyte conducts potassium ions. It should be understood that alkali metal ions are not metallic alkali metal.

[0218] In certain embodiments, the solid electrolyte is in the form of a container. In some cases, the solid electrolyte is in the form of a container that contains the metallic alkali metal of the electrode active material. In certain instances, the solid electrolyte is in the form of a container located within a second container that contains the second electrode.

[0219] In accordance with certain embodiments, the electrochemical cell is configured to produce a metallic metal. For example, as shown in FIG. 90B, in some cases, electrochemical cell 402 is configured to produce metallic metal 408. In some embodiments, the produced metallic metal comprises a produced metallic alkali metal (e.g., metallic sodium metal and / or metallic lithium metal and / or metallic potassium metal). In certain cases, the produced metallic metal (e.g., produced metallic alkali metal) comprises produced metallic sodium metal. In some cases, the produced metallic metal (e.g., produced metallic alkali metal) comprises produced metallic lithium metal. In some cases, the produced metallic metal (e.g., produced metallic alkali metal) comprises produced metallic potassium metal.

[0220] According to certain embodiments, the electrochemical cell comprises a liquid that is inert with respect to the produced metallic metal (e.g., produced metallic sodium and / or produced metallic lithium and / or produced metallic potassium). In some instances, the liquid that is inert with respect to the produced metallic metal comprises an oil. In some embodiments, the liquid that is inert with respect to the produced metallic metal is not flammable. In certain embodiments, the liquid that is inert with respect to the produced metallic metal comprises a hydrophobic liquid. According to some embodiments, the liquid that is inert with respect to the produced metallic metal is a nonaqueous liquid and / or a liquid that does not absorb water.

[0221] #14431536vl According to certain embodiments, the liquid that is inert with respect to the produced metallic metal wets the produced metallic metal (e.g., produced metallic sodium and / or produced metallic lithium and / or produced metallic potassium)

[0222] In accordance with certain embodiments, the electrochemical cell is configured to transport the produced metallic metal directly into the liquid that is inert with respect to the produced metallic metal. In some cases, the density of the liquid that is inert with respect to the produced metallic metal is such that the produced metallic metal is moved away from components within the electrochemical cell with which it might react and / or the liquid that is inert with respect to the produced metallic metal provides a barrier between the produced metallic metal and any components within the electrochemical cell with which it might react (e.g., if the produced metallic metal sinks or floats in the liquid that is inert with respect to the produced metallic metal).

[0223] In some embodiments, the liquid that is inert with respect to the produced metallic metal has a density higher than that of the produced metallic metal in solid state below its melting point and / or in liquid state above its melting point. In certain embodiments, the liquid that is inert with respect to the produced metallic metal has a density such that the produced metallic metal floats in the liquid that is inert with respect to the produced metallic metal when the produced metallic metal is in solid state and / or liquid state.

[0224] In some embodiments, the liquid that is inert with respect to the produced metallic metal has a density lower than that of the produced metallic metal in solid state below its melting point and / or in liquid state above its melting point. In certain embodiments, the liquid that is inert with respect to the produced metallic metal has a density such that the produced metallic metal sinks in the liquid that is inert with respect to the produced metallic metal when the produced metallic metal is in solid state and / or liquid state.

[0225] According to some embodiments, the liquid that is inert with respect to the produced metallic metal has a density intermediate between that of the produced metallic metal in solid state below its melting point and that of the produced metallic metal in liquid state above its melting point. According to certain embodiments, the liquid that is inert with respect to the produced metallic metal has a density such that the produced metallic metal sinks in the solid state and floats in the liquid state and / or the liquid that is inert with respect to the produced metallic metal has a density such that the produced metallic metal floats in the solid state and sinks in the liquid state.

[0226] #14431536vl In some cases, the electrochemical cell is configured such that the alkali metal-containing material is supplied from a source external to the electrochemical cell. For example, in some embodiments, the electrochemical cell is configured such that the alkali metal-containing material is supplied from a source external to the electrochemical cell continuously or intermittently.

[0227] In certain embodiments, the electrochemical cell is configured such that the produced metallic metal can be removed from the electrochemical cell. For example, according to certain embodiments, the electrochemical cell comprises an outlet through which the produced metallic metal can be removed from the electrochemical cell. In some cases, the outlet is configured such that the produced metallic metal can be removed from the electrochemical cell without deforming and / or breaking the electrochemical cell.

[0228] According to some embodiments, the electrochemical cell is configured such that the alkali metal-containing material is supplied from a source external to the electrochemical cell and / or the electrochemical cell is configured such that the produced metallic metal can be removed from the electrochemical cell. For example, in certain cases, the electrochemical cell is configured such that the alkali metal-containing material is supplied from a source external to the electrochemical cell and the electrochemical cell is configured such that the produced metallic metal can be removed from the electrochemical cell.

[0229] In accordance with certain embodiments, the electrochemical cell is a battery, such as a rechargeable battery.

[0230] In certain embodiments, the system comprises an alkali metal fuel cell. Non-limiting examples of such alkali metal fuel cells are shown in FIGs. 29, 32A-32C, 35, 37, 41, 52A, 52B, 67, 69-72, and 90A-90B. For example, as shown in FIGs. 90A and 90B, in some cases, system 400 comprises alkali metal fuel cell 401.

[0231] In some embodiments, the alkali metal fuel cell comprises a cathode (e.g., any cathode disclosed herein). For example, as shown in FIG. 67, in some cases, alkali metal fuel cell 100 comprises cathode 103. As another example, as shown in FIGs. 90A and 90B, in some cases, alkali metal fuel cell 401 comprises cathode 404. In certain embodiments, the cathode comprises a cathodic reactant and / or solids that aid in electron or ion transfer. For example, in some cases, the cathode comprises a cathodic reactant. According to certain embodiments, the cathode comprises a cathodic reactant comprising gaseous oxygen, gaseous water, and / or gaseous carbon dioxide. For example, in some cases, the cathode comprises a cathodic reactant

[0232] #14431536vl comprising gaseous water. In certain instances, the cathode comprises a 2-dimensional cathode. In certain cases, the cathode comprises metal or carbon films, sintered cermets, gas diffusion electrodes, and / or mixed ionic-electronic conductors (MIEC).

[0233] In some embodiments, the alkali metal fuel cell comprises an anode (e.g., any anode disclosed herein). For example, as shown in FIG. 67, in some cases, alkali metal fuel cell 100 comprises anode 101. As another example, as shown in FIGs. 90A and 90B, in some cases, alkali metal fuel cell 401 comprises anode 403. In certain embodiments, the anode comprises an anodic reactant and / or solids that aid in electron or ion transfer. For example, in some cases, the anode comprises an anodic reactant. In certain embodiments, the anode comprises an anodic reactant comprising a metallic metal (e.g., any metallic metal disclosed herein, such as a metallic alkali metal). In accordance with certain embodiments, the anode comprises an anodic reactant comprising an alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal). According to certain embodiments, the anode comprises an anodic reactant comprising a liquid alkali metal (e.g., liquid sodium metal and / or liquid lithium metal and / or liquid potassium metal). For example, in some cases, the anode comprises an anodic reactant comprising a layer of liquid alkali metal (e.g., liquid sodium metal and / or liquid lithium metal and / or liquid potassium metal).

[0234] The layer of liquid alkali metal may have a suitable thickness. For example, in certain embodiments, the layer of liquid alkali metal has a thickness of greater than or equal to 1 millimeter, greater than or equal to 2 millimeters, greater than or equal to 3 millimeters, greater than or equal to 4 millimeters, greater than or equal to 5 millimeters, greater than or equal to 6 millimeters, greater than or equal to 7 millimeters, greater than or equal to 8 millimeters, greater than or equal to 9 millimeters, greater than or equal to 1 centimeter, greater than or equal to 1.1 centimeters, greater than or equal to 1.2 centimeters, greater than or equal to 1.3 centimeters, greater than or equal to 1.4 centimeters, greater than or equal to 1.5 centimeters, greater than or equal to 2.0 centimeters, greater than or equal to 2.5 centimeters, greater than or equal to 3.0 centimeters, greater than or equal to 3.5 centimeters, or greater than or equal to 4.0 centimeters. In some embodiments, the layer of liquid alkali metal has a thickness of less than or equal to 10 centimeters, less than or equal to 9 centimeters, less than or equal to 8 centimeters, less than or equal to 7 centimeters, less than or equal to 6 centimeters, less than or equal to 5 centimeters, less than or equal to 4.8 centimeters, less than or equal to 4.5 centimeters, less than or equal to 4.3 centimeters, less than or equal to 4.0 centimeters, less than or equal to 3.8 centimeters, less

[0235] #14431536vl than or equal to 3.5 centimeters, less than or equal to 3.3 centimeters, less than or equal to 3.0 centimeters, less than or equal to 2.8 centimeters, less than or equal to 2.5 centimeters, less than or equal to 2.3 centimeters, less than or equal to 2.0 centimeters, less than or equal to 1.8 centimeters, less than or equal to 1.5 centimeters, less than or equal to 1.3 centimeters, less than or equal to 1.0 centimeters, or less than or equal to 5 millimeters. Combinations of these ranges are also possible (e.g., greater than or equal to 1 millimeter and less than or equal to 10 centimeters, greater than or equal to 1 millimeter and less than or equal to 5 centimeters, or greater than or equal to 1 millimeter and less than or equal to 2 centimeters).

[0236] According to certain embodiments, the alkali metal fuel cell is configured such that the liquid alkali metal is not replenished during its period of operation. For example, in some cases, the liquid alkali metal layer is sufficiently thick (e.g., a thickness disclosed herein) that the alkali metal is sufficient for the entire period of operation. In certain instances, the period of operation is the intended duration of use of the alkali metal fuel cell. For example, in the case of a vehicle, the period of operation is the intended travel time (e.g., flight time), in some instances. That is, in some cases, the liquid alkali metal is not replenished during the intended travel time (e.g. flight time) of a vehicle (e.g., aviation vehicle).

[0237] In some embodiments, the period of operation is greater than or equal to 10 minutes, greater than or equal to 30 minutes, greater than or equal to 1 hour, greater than or equal to 2 hour, greater than or equal to 3 hours, greater than or equal to 5 hours, greater than or equal to 7 hours, or greater than or equal to 10 hours. In certain embodiments, the period of operation is less than or equal to 1 month, less than or equal to 3 weeks, less than or equal to 2 weeks, less than or equal to 1 week, less than or equal to 5 days, less than or equal to 3 days, less than or equal to 48 hours, less than or equal to 24 hours, less than or equal to 20 hours, less than or equal to 18 hours, less than or equal to 16 hours, less than or equal to 14 hours, less than or equal to 12 hours, less than or equal to 10 hours, or less than or equal to 8 hours. Combinations of these ranges are also possible (e.g., greater than or equal to 10 minutes and less than or equal to 1 month, greater than or equal to 10 minutes and less than or equal to 24 hours, or greater than or equal to 3 hours and less than or equal to 18 hours).

[0238] In accordance with certain embodiments, the alkali metal fuel cell is configured such that the liquid alkali metal is replenished continuously or intermittently during its period of operation.

[0239] #14431536vl In some embodiments, the alkali metal fuel cell comprises a solid electrolyte (e.g., any solid electrolyte disclosed herein). For example, as shown in FIG. 67, in some cases, alkali metal fuel cell 100 comprises optional solid electrolyte 102. As another example, as shown in FIG. 90B, in some cases, alkali metal fuel cell 401 comprises optional solid electrolyte 411. In certain embodiments, the solid electrolyte is below the anode and / or the cathode is below the solid electrolyte in the direction of gravitational pull. For example, in some cases, the solid electrolyte is below the anode and the cathode is below the solid electrolyte in the direction of gravitational pull. For example, as shown in FIG. 67, in some cases, optional solid electrolyte

[0240] 102 is below anode 101 and cathode 103 is below optional solid electrolyte 102 in the direction of gravitational pull. In some embodiments, a discharge product forms on the outside of the cathode. For example, as shown in FIG. 67, in some cases, optional discharge product 104 forms on the outside of cathode 103. In accordance with certain embodiments, the alkali metal fuel cell is configured such that a discharge product exits the cathode in a direction substantially parallel (e.g., within 45 degrees, within 30 degrees, within 15 degrees, or within 5 degrees of parallel, or parallel) to the direction of gravitational pull. For example, as shown in FIG. 67, in some cases, cathode 103 is configured such that optional discharge product 104 exits cathode

[0241] 103 in a direction substantially parallel to the direction of gravitational pull. In some embodiments, the discharge product is convected substantially normal to the direction of gravitational pull during or after exiting the cathode, for example, for the purpose of collecting said discharge product.

[0242] In certain embodiments, the cathode is adherent to the solid electrolyte. In other embodiments, the cathode and solid electrolyte are at least partially separated. In some embodiments, a space between the cathode and the solid electrolyte is at least partially filled by a condensed phase that comprises a discharge product of the fuel cell.

[0243] In some embodiments, the cathode is not bonded to the solid electrolyte. For example, as shown in FIGs. 73A-73B, in some cases, the cathode is not bonded to the solid electrolyte. For example, in some embodiments, the alkali metal fuel cell comprises a liquid alkali metal anode, a solid electrolyte, and a cathode (e.g., air cathode) that is not bonded to the solid electrolyte. In this embodiment, the liquid discharge product may act as a catholyte, providing interfacial contact between the cathode (e.g., air cathode) and the solid electrolyte. In some cases, this liquid discharge product has a high (>100 mS / cm) conductivity for alkali metal cations and

[0244] #14431536vl anions such as, but not limited to, hydroxides. Thus, in certain instances, discharge products form in the catholyte solution, where metal cations meet the oxygen-based anions.

[0245] In certain embodiments, this liquid-phase discharge product is removed by in-plane flow to the edge of the cathode (e.g., air cathode), using the hydrostatic pressure that results from producing a liquid in the confined space between the cathode (e.g., air cathode) and the solid electrolyte. In some embodiments, gravitational pull is used to further facilitate liquid removal. In certain embodiments, the liquid discharge product is removed through channels in the air cathode, which provides for the liquid to leave the cell in the out of plane direction. According to some embodiments, the discharge product removal is augmented by a pump.

[0246] As shown in FIGs. 73A-73B, in some cases, the cathode is not bonded to the solid electrolyte, and the discharge product forms in between the cathode and the solid electrolyte. As shown in FIG. 73A, in certain cases, the discharge product is removed via in-plane flow, while, as shown in FIG. 73B, in some instances, the discharge product is removed via out-of-plane flow.

[0247] In certain embodiments, the solid electrolyte has an anode-facing surface. In some cases, the anode-facing surface comprises a coating. In some cases, the coating comprises a composition that is wetted by the anodic reactant. In certain instances, the coating comprises tin, silver, gold, and / or carbon. Without wishing to be bound by theory, it is believed that the solid electrolyte having an anode-facing surface comprising a coating comprising tin, silver, gold, and / or carbon promotes alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal) wetting of the anode-facing surface and / or provides more uniform electrical contact between the anode-facing surface and the alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal), in some embodiments.

[0248] According to some embodiments, the alkali metal fuel cell is configured to produce a discharge product (e.g., any discharge product disclosed herein). For example, as shown in FIG. 67, in some cases, alkali metal fuel cell 100 is configured to produce optional discharge product 104. As another example, as shown in FIG. 90B, in some cases, alkali metal fuel cell 401 is configured to produce discharge product 407. In some cases, the discharge product comprises an alkali metal hydroxide, an alkali metal oxide, an alkali metal peroxide, an alkali metal carbonate, an alkali metal bicarbonate, an alkali metal oxalate, an alkali metal peroxyoxylate, and / or an alkali metal halide. For example, in certain embodiments, the discharge product comprises an alkali metal hydroxide (e.g., sodium hydroxide and / or lithium hydroxide and / or

[0249] #14431536vl potassium hydroxide). In some cases, the alkali metal hydroxide comprises sodium hydroxide. In certain cases, the alkali metal hydroxide comprises lithium hydroxide. In certain instances, the alkali metal hydroxide comprises potassium hydroxide. In some cases, at least a portion (e.g., at least 10 wt%, at least 25 wt%, at least 50 wt%, at least 75 wt%, at least 90 wt%, or all) of the discharge product is in the form of a liquid solution. For example, in certain instances, the discharge product comprises an alkali metal hydroxide, such as sodium hydroxide and / or lithium hydroxide and / or potassium hydroxide, and at least a portion (e.g., at least 10 wt%, at least 25 wt%, at least 50 wt%, at least 75 wt%, at least 90 wt%, or all) of the alkali metal hydroxide, such as sodium hydroxide and / or lithium hydroxide and / or potassium hydroxide, is in the form of a liquid solution. In certain instances, the liquid solution comprises an aqueous solution.

[0250] In certain embodiments, the alkali metal fuel cell is configured such that at least a portion (e.g., at least 10 wt%, at least 25 wt%, at least 50 wt%, at least 75 wt%, at least 90 wt%, or all) of the discharge product is removed from the alkali metal fuel cell during operation of the alkali metal fuel cell. In some cases, the discharge product is removed intermittently or continuously.

[0251] In accordance with certain embodiments, the alkali metal fuel cell is configured to produce the liquid solution at suitable operating temperatures. For example, in some embodiments, the alkali metal fuel cell is configured to produce the liquid solution at an operating temperature of greater than or equal to 98 °C, greater than or equal to 100 °C, greater than or equal to 105 °C, greater than or equal to 110 °C, greater than or equal to 115 °C, greater than or equal to 120 °C, greater than or equal to 125 °C, greater than or equal to 130 °C, greater than or equal to 135 °C, greater than or equal to 140 °C, greater than or equal to 145 °C, greater than or equal to 150 °C, greater than or equal to 160 °C, greater than or equal to 170 °C, greater than or equal to 180 °C, or greater than or equal to 190 °C. In certain cases, the alkali metal fuel cell is configured to produce the liquid solution at an operating temperature of less than or equal to 323 °C, less than or equal to 320 °C, less than or equal to 310 °C, less than or equal to 300 °C, less than or equal to 290 °C, less than or equal to 280 °C, less than or equal to 270 °C, less than or equal to 260 °C, less than or equal to 250 °C, less than or equal to 240 °C, less than or equal to 230 °C, less than or equal to 220 °C, less than or equal to 210 °C, less than or equal to 200 °C, less than or equal to 190 °C, less than or equal to 180 °C, less than or equal to 170 °C, less than or equal to 160 °C, less than or equal to 150 °C, less than or equal to 145 °C, less than or equal to 140 °C, less than or equal to 135 °C, less than or equal to 130 °C, less than or equal to 125 °C, less than or equal to 120 °C, less than or equal to 115 °C, less than or equal to 110 °C, or less

[0252] #14431536vl than or equal to 105 °C. Combinations of these ranges are also possible (e.g., greater than or equal to 98 °C and less than or equal to 323 °C, greater than or equal to 98 °C and less than or equal to 200 °C, or greater than or equal to 100 °C and less than or equal to 150 °C). In some embodiments, the alkali metal fuel cell is configured to produce the liquid solution at an operating temperature less than, equal to, or greater than, the melting point of the anodic reactant.

[0253] In some embodiments, the anodic reactant comprises an alkali metal reactant. In certain cases, the anodic reactant has a melting point lower than the alkali metal reactant when present as a substantially pure metal. For example, in certain instances, a sodium metal fuel cell comprises an anodic reactant comprising a sodium-potassium alloy having a melting point lower than that of sodium metal, such as a melting point below about 20°C. In certain embodiments, the anodic reactant is a solid at the temperature or temperatures present in the fuel cell during operation.

[0254] In accordance with some embodiments, the alkali metal fuel cell is configured to produce the liquid solution at a suitable water partial pressure. For example, in certain embodiments, the alkali metal fuel cell is configured to produce the liquid solution at a water partial pressure of greater than or equal to 0.03 atm, greater than or equal to 0.05 atm, greater than or equal to 0.07 atm, greater than or equal to 0.1 atm, greater than or equal to 0.12 atm, greater than or equal to 0.15 atm, greater than or equal to 0.2 atm, greater than or equal to 0.3 atm, greater than or equal to 0.4 atm, greater than or equal to 0.5 atm, greater than or equal to 0.6 atm, greater than or equal to 0.7 atm, greater than or equal to 0.8 atm, greater than or equal to 0.9 atm, greater than or equal to 1.0 atm, greater than or equal to 1.1 atm, greater than or equal to 1.2 atm, greater than or equal to 1.3 atm, greater than or equal to 1.4 atm, greater than or equal to 1.5 atm, or greater than or equal to 1.7 atm. In some embodiments, the alkali metal fuel cell is configured to produce the liquid solution at a water partial pressure of less than or equal to 5 atm, less than or equal to 4.8 atm, less than or equal to 4.5 atm, less than or equal to 4.3 atm, less than or equal to 4.0 atm, less than or equal to 3.8 atm, less than or equal to 3.5 atm, less than or equal to 3.3 atm, less than or equal to 3.0 atm, less than or equal to 2.8 atm, less than or equal to 2.5 atm, less than or equal to 2.3 atm, less than or equal to 2.0 atm, less than or equal to 1.8 atm, less than or equal to 1.5 atm, less than or equal to 1.3 atm, less than or equal to 1.0 atm, less than or equal to 0.8 atm, or less than or equal to 0.5 atm. Combinations of these ranges are also possible e.g., greater than or

[0255] #14431536vl equal to 0.03 atm and less than or equal to 5 atm, greater than or equal to 0.1 atm and less than or equal to 3.0 atm, or greater than or equal to 1.2 atm and less than or equal to 2.0 atm).

[0256] In certain embodiments, the alkali metal fuel cell further comprises a separator. Nonlimiting examples of alkali metal fuel cells comprising a separator are shown in FIGs. 69-72. For example, as shown in FIGs. 69-72, in some cases, the alkali metal fuel cell comprises separator 300.

[0257] In some cases, the separator is permeable to the liquid solution (e.g., aqueous solution). For example, in certain instances, at least 50 vol%, at least 75 vol%, at least 90 vol%, or all of the liquid solution can pass through the separator. In some embodiments, the separator is impermeable to the alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal). For example, in certain embodiments, less than 50 vol%, less than 25 vol%, less than 10 vol%, or none of the alkali metal can pass through the separator. In accordance with some embodiments, the separator is permeable to the liquid solution and impermeable to the alkali metal. Without wishing to be bound by theory, it is believed that, in some embodiments, having a separator permeable to the liquid solution and impermeable to the alkali metal reduces contact between the alkali metal and the liquid solution in the instance of a rupture of the alkali metal fuel cell, which would otherwise allow crossover of the alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal).

[0258] It is appreciated that reactions between an alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal) and aqueous solutions may generate hydrogen, which may be combustible under certain conditions. Accordingly, in some embodiments the alkali metal fuel cell includes materials and / or designs that separate alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal) from an aqueous discharge product in the event of a cell membrane failure or leakage of alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal) from the anode side of the cell to the cathode side of the cell. Such a separator may be used anywhere in the alkali metal fuel cell where such separation may be desired.

[0259] It is appreciated that alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal) has a high surface tension and may not wet certain materials, including certain ceramics, metals, and polymers, while aqueous solutions may have a relatively low surface tension and wet certain materials that alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal) does not. Accordingly, in some embodiments, the separator comprises a material that is not wetted by alkali metal (e.g., sodium metal and / or lithium metal and / or

[0260] #14431536vl potassium metal) and is wetted by aqueous solutions, such as alkaline hydroxide solutions, such as sodium hydroxide and / or lithium hydroxide and / or potassium hydroxide solutions. As used herein, “wetting” means a contact angle of a droplet of said alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal), which may be solid or liquid, or said aqueous solution, when placed on said separator material, that is less than about 90 degrees (e.g., less than or equal to 80 degrees, less than or equal to 70 degrees, less than or equal to 60 degrees, less than or equal to 50 degrees, less than or equal to 40 degrees, less than or equal to 30 degrees, or less than or equal to 20 degrees). In some embodiments, wetting of the separator material by said aqueous solution includes the instance where the contact angle is about zero degrees, and spreading of the liquid on the separator material occurs.

[0261] In some embodiments, a mechanical separation of said alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal) and said aqueous solution is produced. For example, in some instances, a mechanical separation of said alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal) and said aqueous solution is produced using a separator comprising a material that is not wetted by alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal) and is wetted by aqueous solutions. A non-limiting example, in accordance with certain embodiments, is the placement of a mesh or screen of such material on the cathode side of the fuel cell such that alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal) is prevented from passing through the mesh or screen due to its high surface tension and non- wetting nature, while any aqueous solution present can pass through, thereby achieving separation. In certain embodiments, the design of the separator mesh or screen varies depending on operating parameters such as the pressure exerted on the alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal), the contact angle of the alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal) and aqueous solution on the separator, and / or the flow rate of aqueous solution away from the separator. In some embodiments, the mesh or screen has perforations with a minimum dimension of greater than or equal to 0.1 mm (e.g., greater than or equal to 0.3 mm, greater than or equal to 0.5 mm, greater than or equal to 0.7 mm greater than or equal to 1 mm, greater than or equal to 2 mm, or greater than or equal to 3 mm) and less than or equal to 5 mm (e.g., less than or equal to 5 mm, less than or equal to 4.5 mm, less than or equal to 4 mm, less than or equal to 3 mm, less than or equal to 2 mm, or less than or equal to 1 mm) (combinations of these ranges are also possible). In some embodiments, the separator is inclined. For example, in certain cases, the separator is

[0262] #14431536vl inclined to cause any alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal) that is caught by it to be diverted to a drain and / or collection system.

[0263] In some embodiments, the alkali metal fuel cell further comprises a drain and / or collection system for the liquid solution (e.g., aqueous solution). In certain instances, the separator is positioned upstream of the drain and / or collection system. For example, as shown in FIG. 71, in some cases, the alkali metal fuel cell comprises separator 300 and / or inclined separator 301, and drain and / or collection system 302.

[0264] According to certain embodiments, the power density of the alkali metal fuel cell increases during operation. Without wishing to be bound by theory, it is believed that the power density of the alkali metal fuel cell increases during operation because the mass of the alkali metal fuel cell decreases during operation as the discharge product is discharged and / or removed, in some embodiments.

[0265] In some embodiments, the system is configured such that the produced metallic metal, such as the produced metallic alkali metal, from the electrochemical cell replenishes the metallic metal, such as the alkali metal, of the anodic reactant from the alkali metal fuel cell. For example, as shown in FIG. 90B, in some cases, system 400 is configured such that metallic metal 408 replenishes the alkali metal of the anodic reactant of anode 403.

[0266] In certain embodiments, the system is configured such that the discharge product (of the alkali metal fuel cell), such as the alkali metal hydroxide discharge product, replenishes the alkali metal-containing material of the second electrode (of the electrochemical cell). For example, as shown in FIG. 90B, in some cases, system 400 is configured such that discharge product 407 replenishes the alkali metal-containing material of second electrode 406.

[0267] According to some embodiments, the metallic alkali metal of the first electrode, the alkali metal-containing material, the alkali metal ions, the produced metallic metal, and / or the alkali metal of the anodic reactant comprise the same metal. For example, in certain cases, the metallic alkali metal of the first electrode, the alkali metal-containing material, the alkali metal ions, the produced metallic metal, and / or the alkali metal of the anodic reactant comprise lithium. As another example, in some instances, the metallic alkali metal of the first electrode, the alkali metal-containing material, the alkali metal ions, the produced metallic metal, and / or the alkali metal of the anodic reactant comprise sodium. As yet another example, in some instances, the metallic alkali metal of the first electrode, the alkali metal-containing material, the alkali metal ions, the produced metallic metal, and / or the alkali metal of the anodic reactant

[0268] #14431536vl comprise potassium. As another example, in some cases, the alkali metal ions (conducted by the solid electrolyte) and the produced metallic metal comprise the same metal. As yet another example, in certain embodiments, the alkali metal-containing material (e.g., alkali metal hydroxide) (of the second electrode) comprises the same metal as the produced metallic metal. In some such cases, the alkali metal-containing material (e.g., alkali metal hydroxide) comprises multiple metals (e.g., a mixed metal hydroxide solution). In some such instances, the alkali metal-containing material (e.g., alkali metal hydroxide) comprises multiple metals (e.g., a mixed metal hydroxide solution) and only one is the same as the produced metallic metal.

[0269] As used herein, a system comprising one or more components (e.g., an electrochemical cell and an alkali metal fuel cell) requires cooperation between the one or more components. For example, in some cases, a product of one component (e.g., a produced metallic metal, such as a produced metallic alkali metal, of an electrochemical cell) is used in the second component (e.g., as the alkali metal of the anodic reactant of the alkali metal fuel cell). In some cases, one or more components of a system, such as an electrochemical cell and alkali metal fuel cell, are connected by one or more pathways, such as structural pathways and / or transportation pathways.

[0270] According to certain embodiments, the electrochemical cell and alkali metal fuel cell are at the same physical location (e.g., within 500 feet, within 250 feet, within 100 feet, within 50 feet, within 25 feet, with 10 feet, or within 5 feet of each other). In some instances, the electrochemical cell and alkali metal fuel cell are structurally connected, such as through one or more structural pathways. For example, in some embodiments, the system comprises one or more structural pathways between the electrochemical cell and alkali metal fuel cell. In some cases, the system comprises a first structural pathway configured to transport the produced metallic metal, such as the produced metallic alkali metal, from the electrochemical cell to the anode of the alkali metal fuel cell (e.g., to replenish the metallic metal, such as the alkali metal, of the anodic reactant). For example, as shown in FIG. 90B, in some cases, system 400 comprises first pathway 409, which is configured to transport metallic metal 408 from electrochemical cell 402 to anode 403 of alkali metal fuel cell 401. In certain cases, the system comprises a second structural pathway configured to transport the discharge product of the alkali metal fuel cell, such as the alkali metal hydroxide discharge product, to the second electrode of the electrochemical cell (e.g., to replenish the alkali metal-containing material of the second electrode). For example, as shown in FIG. 90B, in some cases, system 400 comprises second

[0271] #14431536vl pathway 410, which is configured to transport discharge product 407 from alkali metal fuel cell 401 to second electrode 406 of electrochemical cell 402.

[0272] In some cases, the electrochemical cell and alkali metal fuel cell are at two different physical locations. For example, in certain instances, the electrochemical cell is at a location (e.g., any location disclosed herein), while the alkali metal fuel cell is at a primary site (e.g., any primary site disclosed herein). In some embodiments where the electrochemical cell and alkali metal fuel cell are at two different physical locations, the electrochemical cell and alkali metal fuel cell are connected by one or more transportation pathways. For example, in some embodiments, the system comprises one or more transportation pathways between the electrochemical cell and alkali metal fuel cell. In some cases, the system comprises a first transportation pathway configured to transport the produced metallic metal, such as the produced metallic alkali metal, from the electrochemical cell to the anode of the alkali metal fuel cell (e.g., to replenish the metallic metal, such as the alkali metal, of the anodic reactant). For example, as shown in FIG. 90B, in some cases, system 400 comprises first pathway 409, which is configured to transport metallic metal 408 from electrochemical cell 402 to anode 403 of alkali metal fuel cell 401. In certain cases, the system comprises a second transportation pathway configured to transport the discharge product of the alkali metal fuel cell, such as the alkali metal hydroxide discharge product, to the second electrode of the electrochemical cell (e.g., to replenish the alkali metal-containing material of the second electrode). For example, as shown in FIG. 90B, in some cases, system 400 comprises second pathway 410, which is configured to transport discharge product 407 from alkali metal fuel cell 401 to second electrode 406 of electrochemical cell 402.

[0273] Certain embodiments relate to methods.

[0274] In some embodiments, the method comprises receiving a metallic metal (e.g., any metallic metal disclosed herein, such as any produced metallic metal disclosed herein) from a location. In certain cases, the location is remote from a primary site.

[0275] In certain embodiments, the metallic metal comprises metallic aluminum, metallic magnesium, metallic silicon, metallic calcium, metallic titanium, metallic gallium, and / or a metallic alkali metal. For example, in some cases, the metallic metal comprises metallic alkali metal (e.g., metallic sodium and / or metallic lithium and / or metallic potassium). For example, in certain instances, the metallic metal is metallic sodium. As another example, in certain cases, the metallic metal is metallic lithium. As another example, in certain cases, the metallic metal is potassium.

[0276] #14431536vl According to certain embodiments, the method comprises oxidizing the metallic metal (e.g., any metallic metal disclosed herein, such as any produced metallic metal disclosed herein) to produce oxidized product and energy at the primary site.

[0277] In some cases, oxidizing the metallic metal comprises discharging an alkali metal fuel cell (e.g., any alkali metal fuel cell disclosed herein) to produce an electric current. In certain instances, the produced oxidized product is the discharge product (e.g., any discharge product disclosed herein, such as an alkali metal hydroxide, such as lithium hydroxide and / or sodium hydroxide and / or potassium hydroxide) of the alkali metal fuel cell.

[0278] In accordance with certain embodiments, the method comprises transporting the oxidized product to a secondary site that is remote from the primary site. In some cases, the location that is remote from the primary site (e.g., the location from which the metallic metal is received) is the same as the secondary site that is remote from the primary site (e.g., the secondary site to which the oxidized product is transported). In some embodiments, the metallic metal is produced at the location that is remote from the primary site and / or at the secondary site that is remote from the primary site. In certain embodiments, the metallic metal is produced at the location that is remote from the primary site and / or at the secondary site that is remote from the primary site using an electrochemical cell (e.g., any electrochemical cell disclosed herein). For example, in certain embodiments, the metallic metal (e.g., lithium metal and / or sodium metal and / or potassium metal) is produced at the location that is remote from the primary site and / or at the secondary site that is remote from the primary site from the oxidized product (e.g., any discharge product disclosed herein, such as an alkali metal hydroxide, such as lithium hydroxide and / or sodium hydroxide and / or potassium hydroxide) using an electrochemical cell (e.g., any electrochemical cell disclosed herein).

[0279] In accordance with some embodiments, the method comprises producing the metallic metal. For example, in some cases, the method comprises producing the metallic metal at the location that is remote from the primary site and / or at the secondary site that is remote from the primary site. In certain embodiments, the method comprises producing the metallic metal from a metal hydroxide, a metal oxide, a metal peroxide, a metal carbonate, a metal bicarbonate, a metal oxalate, a metal peroxyoxylate, and / or a metal halide (e.g., at the location that is remote from the primary site). In some embodiments, the method comprises producing the metallic metal from an alkali metal hydroxide, an alkali metal oxide, an alkali metal peroxide, an alkali metal carbonate, an alkali metal bicarbonate, an alkali metal oxalate, an alkali metal

[0280] #14431536vl peroxyoxylate, and / or an alkali metal halide (e.g., at the location that is remote from the primary site). According to some embodiments, the method comprises producing the metallic metal using an electrochemical cell (e.g., any electrochemical cell disclosed herein) (e.g., at the location that is remote from the primary site).

[0281] In some embodiments, the method comprises discharging the alkali metal fuel cell (e.g., any alkali metal fuel cell disclosed herein) to produce an electric current. In certain embodiments, the method comprises replenishing the metallic metal, such as the alkali metal, of the anodic reactant with the produced metallic metal, such as the produced metallic alkali metal. In accordance with some embodiments, the method comprises replenishing the alkali metalcontaining material of the second electrode of the electrochemical cell with the discharge product (e.g., the alkali metal hydroxide discharge product) of the alkali metal fuel cell.

[0282] According to some embodiments, the location that is remote from the primary site is at least 5 miles, at least 10 miles, at least 25 miles, at least 50 miles, at least 100 miles, at least 250 miles, at least 500 miles, at least 750 miles, or at least 1,000 miles away from the primary site. In certain cases, the location that is remote from the primary site is less than or equal to 10,000 miles, less than or equal to 9,000 miles, less than or equal to 8,000 miles, less than or equal to 7,000 miles, less than or equal to 6,000 miles, less than or equal to 5,000 miles, less than or equal to 4,000 miles, less than or equal to 3,000 miles, less than or equal to 2,000 miles, or less than or equal to 1,000 miles away from the primary site. Combinations of these ranges are also possible (e.g., at least 5 miles and less than or equal to 10,000 miles).

[0283] In accordance with some embodiments, the secondary site that is remote from the primary site is at least 5 miles, at least 10 miles, at least 25 miles, at least 50 miles, at least 100 miles, at least 250 miles, at least 500 miles, at least 750 miles, or at least 1,000 miles away from the primary site. In some instances, the secondary site that is remote from the primary site is less than or equal to 10,000 miles, less than or equal to 9,000 miles, less than or equal to 8,000 miles, less than or equal to 7,000 miles, less than or equal to 6,000 miles, less than or equal to 5,000 miles, less than or equal to 4,000 miles, less than or equal to 3,000 miles, less than or equal to 2,000 miles, or less than or equal to 1,000 miles away from the primary site. Combinations of these ranges are also possible (e.g., at least 5 miles and less than or equal to 10,000 miles).

[0284] In certain embodiments, the cost of electricity at the secondary site is lower than the cost of electricity at the primary site at the time the oxidized product is shipped from the primary site

[0285] #14431536vl to the secondary site and / or at the time the oxidized product is received at the secondary site from the primary site. For example, in some instances, the cost of electricity at the secondary site is at least 5%, at least 10%, at least 20%, at least 30%, at least 40%, or at least 50% lower than the cost of electricity at the primary site at the time the oxidized product is shipped from the primary site to the secondary site and / or at the time the oxidized product is received at the secondary site from the primary site. In some embodiments, the cost of electricity at the secondary site is less than 100%, less than or equal to 90%, less than or equal to 80%, less than or equal to 70%, less than or equal to 60%, or less than or equal to 50% lower than the cost of electricity at the primary site at the time the oxidized product is shipped from the primary site to the secondary site and / or at the time the oxidized product is received at the secondary site from the primary site. Combinations of these ranges are also possible (e.g., at least 5% and less than 100% lower).

[0286] In some embodiments, the cost of electricity at the location that is remote from the primary site is lower than the cost of electricity at the primary site at the time the metallic metal is shipped from the location that is remote from the primary site to the primary site and / or at the time the metallic metal is received at the primary site from the location that is remote from the primary site. For example, in some instances, the cost of electricity at the location that is remote from the primary site is at least 5%, at least 10%, at least 20%, at least 30%, at least 40%, or at least 50% lower than the cost of electricity at the primary site at the time the metallic metal is shipped from the location that is remote from the primary site to the primary site and / or at the time the metallic metal is received at the primary site from the location that is remote from the primary site. In some embodiments, the cost of electricity at the location that is remote from the primary site is less than 100%, less than or equal to 90%, less than or equal to 80%, less than or equal to 70%, less than or equal to 60%, or less than or equal to 50% lower than the cost of electricity at the primary site at the time the metallic metal is shipped from the location that is remote from the primary site to the primary site and / or at the time the metallic metal is received at the primary site from the location that is remote from the primary site. Combinations of these ranges are also possible (e.g., at least 5% and less than 100% lower).

[0287] According to certain embodiments, when the metallic metal is received from the location that is remote from the primary site, greater than or equal to 10 kilograms, greater than or equal to 20 kilograms, greater than or equal to 30 kilograms, greater than or equal to 40 kilograms, greater than or equal to 50 kilograms, greater than or equal to 75 kilograms, greater than or equal

[0288] #14431536vl to 100 kilograms, greater than or equal to 200 kilograms, greater than or equal to 300 kilograms, greater than or equal to 400 kilograms, or greater than or equal to 500 kilograms of the metallic metal is received. In some instances, when the metallic metal is received from the location that is remote from the primary site, less than or equal to 3,000 kilograms, less than or equal to 2,000 kilograms, less than or equal to 1,000 kilograms, less than or equal to 900 kilograms, less than or equal to 800 kilograms, less than or equal to 700 kilograms, less than or equal to 600 kilograms, less than or equal to 500 kilograms, less than or equal to 400 kilograms, less than or equal to 300 kilograms, or less than or equal to 200 kilograms of the metallic metal is received.

[0289] Combinations of these ranges are also possible (e.g., greater than or equal to 10 kilograms and less than or equal to 3,000 kilograms, greater than or equal to 100 kilograms and less than or equal to 3,000 kilograms, or greater than or equal to 500 kilograms and less than or equal to 3,000 kilograms).

[0290] In accordance with some embodiments, when the metallic metal is received from the location that is remote from the primary site, the metallic metal is not contained within a battery or other electrochemical cell.

[0291] As a non-limiting example in which sodium salt is thermochemically reduced to the metal, sodium oxide, Na2<D, may be heated to a temperature above about 650°C in an atmosphere with oxygen partial pressure less than about 10'8atm, conditions which result in decomposition into sodium and oxygen vapor. The vapor may be cooled in the presence of another compound including but not limited to calcium, silicon, magnesium, or aluminum, which serve as oxygen getters, producing an oxidized version of the getter compound and pure sodium metal.

[0292] Non-limiting examples in which said sodium salt is electrochemically reduced to the metal include the use of an electrochemical cell to decompose the sodium salt to sodium metal at a cathode and a solid, liquid, or gas comprising the anion species of the salt. In some embodiments, said electrochemical cells comprise a solid electrolyte, which may be a solid sodium ion conductor such as one in the general structural and compositional families known as sodium beta aluminas or sodium (Na) super ionic conductor (NaSICON). Said solid electrolytes also include the lithium and potassium counterparts to the beta aluminas and NaSICONs, for example, including lithium super ionic conductor (LiSICON) or potassium beta aluminas. Advantages to the use of a solid electrolyte may include, in accordance with certain embodiments, a wide electrochemical window affording stability of the solid electrolyte at both

[0293] #14431536vl highly reducing and highly oxidizing conditions, a high sodium ion conductivity allowing high operating current densities and power densities and decreased overpotentials, and high selectivity for the conducting ion which improves the purity of the electrolytically produced metal and allows for the use of less pure feedstock materials. In addition, use of a solid electrolyte may, in accordance with some embodiments, allow for smaller distances between the cathode and anode. In many traditional processes, if the inter-electrode distance is too small, there is a risk of shorting the cell via the metal that is produced. This risk can be mitigated (e.g., fully mitigated) by the presence of a solid-state electrolyte between the two electrodes. The reduction in distance between the anode and the cathode reduces the overpotential of the cell, in accordance with certain embodiments. Several examples are provided below where sodium salts are electrolytically reduced to sodium metal according to the materials, devices, subsystems, systems, or methods of use in accordance with various embodiments.

[0294] FIG. 75 shows an electrochemical cell for sodium production using sodium sulfide or polysulfide feedstock, in accordance with certain embodiments.

[0295] FIG. 76 shows an electrochemical cell for sodium production using molten sodium hydroxide feedstock, according to some embodiments.

[0296] FIGS. 77A-77D show systems comprising different arrangements of sodium production, sodium oxidation, and sodium reduction subsystems, in accordance with certain embodiments. In FIG. 77A, sodium production and reduction occur in one location where sodium precursor may be abundant, while sodium oxidation occurs in another location where energy demand is high. In FIG. 77B, sodium reduction may occur at a location distinct from sodium production and oxidation, where energy may be inexpensive. In FIG. 77C, the oxidant is transported along with the sodium from the reduction subsystem to the oxidation subsystem. In FIG. 77D, the oxidants for the sodium production and sodium reduction subsystems are used for another purpose or discarded.

[0297] In one example, the sodium salt comprises molten or aqueous sodium sulfide or polysulfide, Na2Snwhere 1 < n < 5, the solid electrolyte may be Na-beta” alumina or NaSICON, and the electrochemical cell comprises a cathode at which sodium ions are reduced to sodium metal, and an anode at which sulfide or polysulfide ions are oxidized to elemental sulfur. Such an electrochemical cell is illustrated in FIG. 75. The cathode half-reaction may be: while the anode half-reaction may be:

[0298] #14431536vl Sn2’ <-> nS° + 2e , and the overall cell reaction may be:

[0299] Na2Sn2Na + nS.

[0300] Such an electrochemical cell may be operated below the melting point of sodium metal, which is approximately 98°C, such that the sodium metal is produced as a solid, between the melting point of sodium metal and the melting point of sulfur, which is approximately 116°C, such that sodium metal is produced as a liquid and sulfur as a solid, or above the melting point of sulfur, such that both sodium and sulfur are produced as liquids. The sulfur may co-exist with sodium sulfide as a solid phase. Cathode materials for such cells can be selected to comprise an electronically conductive material that is stable in contact with elemental sodium, including but not limited to material such as metals, carbon, metal carbides, metal nitrides, and composites comprising at least one of said materials, including cermets comprising a metallic phase and a ceramic phase. Anode materials for such cells are selected to comprise an electronically conductive material that is stable in contact with elemental sulfur, including but not limited to material such as metals, carbon, metal carbides, metal nitrides, and composites comprising at least one of said materials, including cermets comprising a metallic phase and a ceramic phase. A non-limiting combination of cathode and anode comprises steel and carbon felt, respectively.

[0301] In another example, the sodium salt comprises molten sodium hydroxide, NaOH, and the solid electrolyte may be Na-beta’ ’ alumina or NaSICON. The electrochemical cell may comprise an iron, steel, or nickel vessel, an anode comprising iron or nickel, an anode chamber containing sodium metal or sodium-bearing alloys in solid or liquid form, a cathode chamber comprising molten sodium hydroxide, aqueous sodium hydroxide solution, or a two-phase mixture of aqueous sodium hydroxide and a solid sodium hydroxide hydrate, and a cathode comprising iron or steel or nickel. Such an electrochemical cell is illustrated in FIG. 76. The cathode half-reaction may be:

[0302] 2Na++ 2e~ -> 2Na, while the anode half-reaction may be:

[0303] 4OH~ ~^ 02+ 2H2O + 4e~, and the overall cell reaction may be:

[0304] 4NaOH -► 4Na + 2H2O + O2.

[0305] This method and electrolyzer design, wherein the anode and cathode chambers are separated by an ion-selective membrane, has advantages over the known Castner process of

[0306] #14431536vl sodium production via electrolysis of molten sodium hydroxide in a single chamber design. The Castner cell consists of a cathode and an anode submerged in a sodium hydroxide melt, operating above the melting temperature of sodium hydroxide (323°C). However, the crossover or diffusion of water produced at the cathode towards the anode results in reduced electrolytic efficiency via two mechanisms. First, the water reacts with the sodium to produce sodium hydroxide and hydrogen gas: 2Na + 2H2O -> H2+ 2Na++ 2OH~, and second, the water undergoes electrolysis when present at the anode and cathode. Both are advantageously avoided in accordance with certain embodiments described herein. In general, and in multiple embodiments, the electrochemical cell uses an ion-selective membrane that has a low permeability to water and / or hydroxyl, and allows electrolytic production of sodium metal or sodium bearing alloys from aqueous feedstocks comprising a sodium salt or the hydrate compounds of sodium salts. The use of such aqueous feedstocks may be advantageous in allowing lower temperature operation, use of lower cost feedstocks, amongst other advantages. For example, use of a sodium hydroxide solution to produce sodium metal may allow cell operation at temperatures below the melting point of sodium hydroxide NaOH (323°C), use of a sodium polysulfide solution may allow cell operation at temperatures below the melting point of sodium sulfide Na2S (1176°C for anhydrous Na2S) to as low as 100°C for sodium sulfide pentahydrate or even 50°C for the nonahydrate, and use of a sodium chloride solution may allow cell operation at temperatures below the melting point of sodium chloride NaCl (801 °C) including as low as room temperature or below, for aqueous solutions of NaCl.

[0307] In another example, said sodium salt comprises NaCl, which may be used in a mixture or solution with another metal halide. In some embodiments said NaCl is mixed with a metal halide that results in a lower melting point for at least some compositions of the mixture, such as CaCh. The solid electrolyte of said electrochemical cell may be Na-beta’ ’ alumina or NaSICON, and the electrochemical cell comprises a cathode at which sodium ions are reduced to sodium metal, and an anode at which chloride anions are oxidized to molecular chlorine, including chlorine gas. Said chlorine produced by the electrochemical reaction may be stored as molecular chlorine in a gaseous or liquid form and re-used in the sodium oxidation reaction, as illustrated in FIG. 77C. Said chlorine may also be reacted chemically or electrochemically to another chlorine-bearing species, including but not limited to chlorine dioxide, which species may subsequently be reacted with sodium metal or alloys comprising sodium, or said species

[0308] #14431536vl may be decomposed to form molecular chlorine which is reacted with sodium metal or alloys comprising sodium.

[0309] Said chlorine produced by said electrochemical reaction may be sold or used for other purposes, as shown in FIG. 77D, and a supply of chlorine later provided for the sodium metal oxidation reaction. That is, the oxidizer originally produced while producing said sodium metal need not be the oxidizer subsequently used in the sodium oxidation reaction producing thermal or electrical energy. More generally, a different anion may be used in a sodium metal producing reaction than is used as the oxidant for energy production. For example, sodium metal may be produced via electrolysis of sodium chloride, and subsequently oxidized by oxygen or water or sulfur for energy generation.

[0310] As examples of end applications for the devices, processes, subsystems, facilities, and systems described herein, in accordance with certain embodiments, consider that intermittent energy sources may be inconveniently located relative to energy demand, necessitating efficient methods of transporting energy. An example of a system that may satisfy such a need comprises (or consists of) a sodium metal-air facility comprising electrochemical cells capable of delivering electricity located at close proximity to an energy demand, and an electrolysis facility located at close proximity to an intermittent energy source. (See, e.g., FIG. 77A.) In such a scheme, the electrolysis facility can consume sodium hydroxide and intermittent energy and produce sodium, while the sodium metal-air facility, which may comprise rechargeable battery cells or discharge-only primary battery cells or fuel cells, may consume sodium and produce sodium hydroxide and reliable energy. In some such embodiments, sodium is transported from the electrolysis facility to the sodium metal-air facility, and sodium hydroxide is transported from the sodium metal-air primary facility to the electrolysis facility.

[0311] Some non-limiting examples of systems are shown in FIGs. 29, 32C, 35, 68, and 72.

[0312] In some embodiments, the system comprises an alkali metal fuel cell (e.g., any alkali metal fuel cell disclosed herein). For example, as shown in FIG. 68, in some cases, system 200 comprises alkali metal fuel cell 100. In accordance with certain embodiments, the system comprises multiple alkali metal fuel cells. For example, as shown in FIG. 32C and FIG. 72, in some cases, the system comprises multiple alkali metal fuel cells. In some embodiments, the system comprises multiple alkali fuel cells electrically connected in series, resulting in a net voltage which is the sum of the voltages of the cells. In certain embodiments, the net voltage is greater than or equal to 2 volts e.g., greater than or equal to 5 volts, greater than or equal to 10

[0313] #14431536vl volts, greater than or equal to 25 volts, greater than or equal to 50 volts, greater than or equal to 100 volts, greater than or equal to 200 volts, greater than or equal to 300 volts, greater than or equal to 400 volts, or greater than or equal to 500 volts) and less than or equal to 1000 volts (e.g., less than or equal 950 volts, less than or equal 900 volts, less than or equal 800 volts, less than or equal 700 volts, less than or equal 600 volts, less than or equal 500 volts, less than or equal 250 volts, or less than or equal 100 volts) (combinations of these ranges are also possible). In certain embodiments, the system comprises multiple alkali fuel cells electrically connected in parallel, resulting in a net current which is the sum of the currents of the cells.

[0314] According to some embodiments, the system comprises a suitable number of cells connected in series and parallel configuration. For example, in certain embodiments, the system comprises greater than or equal to 2, greater than or equal to 10, greater than or equal to 50, greater than or equal to 100, greater than or equal to 200, or greater than or equal to 500 alkali metal fuel cells. According to some embodiments, the system comprises less than or equal to 1000, less than or equal to 600, less than or equal to 400, less than or equal to 300, less than or equal to 200, less than or equal to 100, less than or equal to 50, less than or equal to 20, or less than or equal to 10 alkali metal fuel cells. Combinations of these ranges are also possible (e.g., greater than or equal to 2 and less than or equal to 1000, greater than or equal to 2 and less than or equal to 20, greater than or equal to 50 and less than or equal to 100, or greater than or equal to 2 and less than or equal to 10).

[0315] In some instances, the multiple alkali metal fuel cells may be the same or different. For example, in some cases, the multiple alkali metal fuel cells are each the same. In other cases, the multiple alkali metal fuel cells are each different. In yet other cases, some of the multiple alkali metal fuel cells are the same and some are different.

[0316] According to certain embodiments, the multiple alkali metal fuel cells are stacked. For example, in some instances, the multiple alkali metal fuel cells are stacked substantially parallel (e.g., within 45 degrees, within 30 degrees, within 15 degrees, or within 5 degrees of parallel, or parallel) to the direction of gravitational pull.

[0317] In accordance with some embodiments, the system comprises an electrochemical cell (e.g., any electrochemical cell disclosed herein). For example, as shown in FIG. 68, in some cases, system 200 comprises optional electrochemical cell 202. For example, in certain instances, the system comprises an electrochemical cell (e.g., any electrochemical cell disclosed herein) and an alkali metal fuel cell (e.g., any alkali metal fuel cell disclosed herein). For

[0318] #14431536vl example, as shown in FIG. 68, in some cases, system 200 comprises optional electrochemical cell 202 and alkali metal fuel cell 100. In certain embodiments, the electrochemical cell comprises a solid-electrolyte electrochemical cell. In some cases, the solid-electrolyte electrochemical cell comprises an alkali metal-conducting solid electrolyte. For example, as shown in FIG. 68, in some cases, optional electrochemical cell 202 comprises alkali metalconducting solid electrolyte 203. For example, in some embodiments, the solid electrolyte conducts the same alkali metal (e.g., sodium and / or lithium and / or potassium) as comprised within the anode of the alkali metal fuel cell (e.g., sodium and / or lithium and / or potassium).

[0319] In certain embodiments, the solid-electrolyte electrochemical cell is configured to produce the alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal). For example, in some instances, the solid-electrolyte electrochemical cell is configured to produce the alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal) from an alkali metal salt (e.g., NaCl and / or LiCl). In certain cases, the solid-electrolyte electrochemical cell is configured to produce the alkali metal (e.g., sodium metal and / or lithium metal and / or potassium metal) from an alkali metal salt combined with another chloride salt (e.g., XCl-ZCly, wherein X is the alkali metal, such as sodium and / or lithium and / or potassium, Z is another metal, and y is a number, such as a whole number from 1-10). In some embodiments, Z lowers the melting point of the chloride mixture compared to XC1 alone. In some embodiments, Z is Al or Ca. According to some embodiments, y is 3. For example, in certain embodiments, ZClyis AlCh or CaCh. For example, in some cases, the solid-electrolyte electrochemical cell is configured to produce sodium metal from NaCl combined with AlCh, lithium metal from LiCl combined with AICI3, or potassium metal from KC1 combined with AlCh In some embodiments, the alkali metal produced (e.g., sodium metal and / or lithium metal and / or potassium metal) is transported to and / or used in the alkali metal fuel cell (e.g., in the anode).

[0320] In accordance with certain embodiments, the system comprises an alkali metal storage and handling system (e.g., any storage and handling system disclosed herein). For example, as shown in FIG. 68, in some cases, system 200 comprises optional alkali metal storage and handling system 201. In some embodiments, the system comprises an alkali metal storage and handling system (e.g., any storage and handling system disclosed herein) and an alkali metal fuel cell (e.g., any alkali metal fuel cell disclosed herein). For example, as shown in FIG. 68, in some cases, system 200 comprises optional alkali metal storage and handling system 201 and alkali metal fuel cell 100. For example, in certain instances, the system comprises an alkali

[0321] #14431536vl metal storage and handling system (e.g., any storage and handling system disclosed herein) and an alkali metal fuel cell (e.g., any alkali metal fuel cell disclosed herein) and an electrochemical cell (e.g., any electrochemical cell disclosed herein). For example, as shown in FIG. 68, in some cases, system 200 comprises optional alkali metal storage and handling system 201 and alkali metal fuel cell 100 and optional electrochemical cell 202. In some cases, the alkali metal storage and handling system comprises petroleum or silicone oil.

[0322] According to some embodiments, the alkali metal (e.g., in the alkali metal fuel cell, of the alkali metal storage and handling system, and / or in the electrochemical cell) comprises lithium, sodium, potassium, rubidium, cesium, and / or francium. For example, in certain embodiments, the alkali metal (e.g., in the alkali metal fuel cell, of the alkali metal storage and handling system, and / or in the electrochemical cell) comprises lithium, sodium, and / or potassium. As another example, in some instances, the alkali metal (e.g., in the alkali metal fuel cell, of the alkali metal storage and handling system, and / or in the electrochemical cell) comprises sodium. As another example, in some instances, the alkali metal (e.g., in the alkali metal fuel cell, of the alkali metal storage and handling system, and / or in the electrochemical cell) comprises lithium. As another example, in some instances, the alkali metal (e.g., in the alkali metal fuel cell, of the alkali metal storage and handling system, and / or in the electrochemical cell) comprises potassium. In certain embodiments, the alkali metal is metallic. For example, in some embodiments, the sodium is sodium metal (i.e., metallic sodium). As another example, in some embodiments, the lithium is lithium metal (i.e., metallic lithium). As another example, in some embodiments, the potassium is potassium metal (i.e., metallic potassium).

[0323] According to some embodiments, the alkali metal is solid and / or liquid. For example, in some cases, the alkali metal is liquid, such as molten alkali metal. For example, in certain instances, the alkali metal is liquid sodium metal, such as molten sodium metal. As another example, in certain instances, the alkali metal is liquid lithium metal, such as molten lithium metal. As another example, in certain instances, the alkali metal is liquid potassium metal, such as molten potassium metal.

[0324] In certain cases, the alkali metal is the same or different throughout the system (e.g., in the alkali metal fuel cell, of the alkali metal storage and handling system, and / or in the electrochemical cell). For example, in some cases, the alkali metal (e.g., sodium and / or lithium

[0325] #14431536vl and / or potassium) is the same throughout the system (e.g., in the alkali metal fuel cell, of the alkali metal storage and handling system, and / or in the electrochemical cell).

[0326] Certain embodiments relate to methods (e.g., any methods disclosed herein). In some embodiments, the method comprises discharging an alkali metal fuel cell (e.g., any alkali metal fuel cell disclosed herein) to produce an electric current. In some cases, the method comprises producing a discharge product (e.g., any discharge product disclosed herein, such as sodium hydroxide and / or lithium hydroxide and / or potassium hydroxide). In certain instances, during the discharging, the discharge product exits the cathode in a direction substantially parallel (e.g., within 45 degrees, within 30 degrees, within 15 degrees, or within 5 degrees of parallel, or parallel) to the direction of gravitational pull. In accordance with certain embodiments, the method comprises removing at least a portion (e.g., at least 10 wt%, at least 25 wt%, at least 50 wt%, at least 75 wt%, at least 90 wt%, or all) of the discharge product from the alkali metal fuel cell during operation.

[0327] According to some embodiments, the liquid alkali metal is not replenished during the discharging. For example, in certain embodiments, the method comprises discharging an alkali metal fuel cell for the intended duration of use (e.g., the intended travel time of a vehicle) of the alkali metal fuel cell without replenishing the liquid alkali metal.

[0328] In accordance with certain embodiments, the method comprises replenishing the alkali metal in the alkali metal fuel cell continuously or intermittently during its period of operation.

[0329] In accordance with some embodiments, the method comprises using the discharge product and / or a downstream product thereof to capture and / or sequester atmospheric carbon dioxide and / or to decrease the acidity of a body of water, such as ocean liming. For example, in some cases, the discharge product is sodium hydroxide and the method comprises using the sodium hydroxide to capture atmospheric carbon dioxide. As another example, in certain instances, the discharge product is sodium hydroxide and the method comprises converting the sodium hydroxide to a downstream product. In some cases, the downstream product is sodium carbonate and / or sodium bicarbonate. In certain instances, the sodium carbonate and / or sodium bicarbonate is enriched in carbon dioxide compared to the discharge product prior to exposure to carbon dioxide. For example, in some embodiments, using the sodium hydroxide to capture atmospheric carbon dioxide results in formation of sodium carbonate, which can optionally be further converted to sodium bicarbonate. In certain embodiments, the method comprises using the sodium bicarbonate to decrease the acidity of a body of water.

[0330] #14431536vl In certain embodiments, the method comprises using a discharge product comprising sodium hydroxide to capture carbon dioxide from the atmosphere, or from a source including but not limited to the product of a combustion process. In some embodiments, said combustion process comprises the combustion of coal or a hydrocarbon. In some embodiments, the carbon dioxide results from the decomposition of a carbonate mineral, including but not limited to limestone. Processes yielding carbon dioxide which may be captured by the method in accordance with some embodiments include but are not limited to combustion of fuels to produce energy, cement production, steel production, or ammonia production.

[0331] In some embodiments, an objective is to deliver a power source that offers specific energy >1000Wh / kg at a continuous power density of >500 W / kg and an electricity cost of <$0.30 / kWh. In other embodiments, an objective is to deliver a power source that offers specific energy >1000Wh / kg at a continuous power density of >100 W / kg and an electricity cost of <$0.20 / kWh. In still other embodiments, an objective is to deliver a power source that offers specific energy >1000Wh / kg at a continuous power density of <100 W / kg and an electricity cost of <$0.15 / kWh.

[0332] According to certain embodiments, the technology is a sodium- air fuel cell that uses a solid electrolyte and consumes liquid sodium, producing a solid discharge product that is intermittently or continuously removed from the exterior of the air cathode. In some cases, the re-usable power pack can be continuously or intermittently refueled with sodium metal. In certain instances, alongside the power cell, subsystems for low-cost sodium production from NaCl and for the safe storage and handling of sodium metal are provided, providing an end-to- end system for using sodium metal as a high energy density energy carrier.

[0333] High-energy density metal-air batteries are frequently more efficient when discharging than when charging. Notably, thirty years of R&D have failed to produce a commercial rechargeable Li-air battery. However, discharge energy densities have been demonstrated which may project to systems meeting the present targets, in some instances. In accordance with certain embodiments, for a use-once fuel cell approach, sodium is used due to its low cost and high abundance. In accordance with certain embodiments, for a fuel cell approach wherein a metal is consumed but not recharged in the same device, sodium is used due to its low cost and high abundance. In addition, valorization of chlorine from Na metal production, and the discharge products of the Na-air cell, can further reduce the cost of delivered electricity, perform carbon

[0334] #14431536vl capture and storage (CCS) functions, and / or supply valuable NaOH to other markets, in accordance with certain embodiments.

[0335] In certain embodiments, the sodium- air cell features a refillable sodium metal anode and a removable discharge product. For example, described herein is a sodium-air cell that features a refillable sodium metal anode and a removable solid discharge product, in accordance with some embodiments. In some cases, the strategy includes identifying suitable Na-ion solid electrolytes and cathode materials, integrating these with low-cost interconnect and housing materials, and performing technoeconomic analyses to identify pathways to the cost targets. Described herein, in accordance with certain embodiments, is a solid-electrolyte based electrolysis cell for the production of Na metal and Ch gas from molten chlorides, including but not limited to NaCl-AlCh. For example, described herein, in accordance with certain embodiments, is a solid-electrolyte based electrolysis cell for the production of Na metal and Ch gas from molten chlorides, beginning with NaCl-AlCh. In certain embodiments, the disclosed sodium air cell comprises an electrochemical cell for lower energy consumption and direct purification of input salts, to lower the cost of Na metal production to <$0.30 / kg-Na and delivering high energy density electricity from the Na-air cell at an LCOS of <$0.30 / kWh. For example, the disclosed sodium air cell comprises a Downs cell for lower energy consumption and direct purification of input salts, to lower the cost of Na metal production to <$0.30 / kg-Na and delivering high energy density electricity from the Na-air cell at an LCOS of <$0.30 / kWh, in some embodiments. Also disclosed is a buoyancy-based system for safe storage, handling and delivery of Na metal using non-reactive liquids with density in between that of solid and liquid Na, in certain embodiments.

[0336] In certain embodiments, an onboard power system providing >1,000 Wh / kg and >1000 Wh / L can address close to 80% of all aircraft departures and over 30% of current total jet fuel consumption and its associated emissions (FIG. 30). Metal-air chemistries may have the requisite theoretical energy, but as a battery, none has reached the performance and cost metrics needed for electric aviation, or indeed of any commercial application. In accordance with some embodiments, the disclosed system (FIG. 29) combines several insights: a) Metal-air discharge reactions are much more efficient than charge reactions; b) Those that use the cation as the working ion (Li-air and Na-air) form discharge product on the exterior of the air electrode, from which it can be removed; c) Sodium uniquely has a cost entitlement low enough to meet the LCOS cost targets of many applications without recharging; and d) Discharge products of the

[0337] #14431536vl Na-air cell as well as chlorinated co-products from Na metal production can be valorized to further reduce LCOS.

[0338] In accordance with certain embodiments, the proposed sodium metal-based power system combines three subsystems shown in FIG. 29. In certain embodiments, the first subsystem is a sodium-air fuel cell that uses liquid Na, a solid electrolyte, and has a removable discharge product. For example, in some embodiments, the first subsystem is a sodium-air fuel cell that uses liquid Na, a solid electrolyte, and has a removable solid discharge product. Using liquid sodium avoids well-known failure modes of solid metal anodes, in some cases. In certain embodiments, discarding the discharge product in flight reduces mass and increases energy density. The Ragone plot in FIG. 31 shows that a Na-air cell of such design can reach pulse power density of 3000 W / kg and continuous-discharge energy density of 1500 Wh / kg. Retaining the oxygen onboard in a discharge product may also allow these targets to be reached, in certain instances. For example, the Ragone plot in FIG. 31 shows that a Na-air cell of this design can reach pulse power density of 3000 W / kg and continuous-discharge energy density of 1500 Wh / kg, while retaining the oxygen onboard just reaches the FOA targets, in certain instances. Note that, in certain embodiments, a IMWh flight produces only 0.27 m3of an exemplary discharge product, Na2O2, which is a negligible amount when distributed over a 100- 200-mile flight path. For example, note that, in some embodiments, a IMWh flight produces only 0.27 m3of Na2O2, a negligible amount when distributed over a 100-200-mile flight path. According to some embodiments, when exposed to humidity and atmospheric CO2, an exemplary discharge product NaxOyspontaneously converts to sodium bicarbonate (NaHCOs), capturing 0.92 tonnes CO2 per MWh in addition to the averted fossil fuel emissions. For example, according to certain embodiments, when exposed to humidity and atmospheric CO2, NaxOyspontaneously converts to sodium bicarbonate (NaHCOs), capturing 0.92 tonnes CO2 per MWh in addition to the averted fossil fuel emissions. If discharged into the ocean, the sodium bicarbonate has the further benefit of deacidification, in some instances. According to some embodiments, a flight of ~10h consumes -lOmrn of Na (capacity ~lAh / cm2) and does not require continuous delivery of Na. For example, according to certain embodiments, a flight of ~10h consumes -lOmrn of Na (capacity ~lAh / cm2) and does not require continuous delivery of Na, but removal of the discharge product is necessary for energy density and to maintain power. In certain instances, multi-cell modules as in FIG. 32C can be rapidly swapped to recharge, and the depleted modules refilled with Na metal (the only consumable of the reaction which needs to

[0339] #14431536vl be provided) offline. For example, in some instances, multi-cell modules as in FIG. 32C can be rapidly swapped to recharge, and the depleted modules refilled with Na metal (the only consumable) offline. For Na metal at a cost of $0.30 / kg-Na, the LCOS is $0.18 / kWh, in some cases. Monetization of discharge products can further reduce this cost, in certain instances. For example, in some cases, at $100 / tonne CO2 price, CCS via sodium bicarbonate reduces LCOS by $0.08 / kWh. As another example, in certain instances, an alternative co-product, high purity NaOH, would reduce LCOS by $0.16 / kWh at current market price of ~$400 / tonne (while lowering energy density). In accordance with some embodiments, the second subsystem is a solid-electrolyte electrochemical cell (FIG. 29) for low-cost electrolytic production of Na metal from metal chlorides. Na metal may be made electrolytically from NaCl-CaCh eutectic melts using the Downs cell operating at an overpotential of 3.5V (7.1V total). The solid electrolyte cell, according to certain embodiments, may operate as low as 4.5V, use a lower-melting eutectic such as NaCl-AlCL, and produce higher purity Na at a target cost of $0.30 / kg-Na. For example, the solid electrolyte cell, according to some embodiments of the invention, may operate at 4.5V, use a lower-melting eutectic such as NaCl-AlCL, and produce higher purity Na at a target cost of $0.30 / kg-Na. Monetization of the Ch co-product has the potential to reduce Na metal cost by $0.46 / kg-Na, in some cases. According to certain embodiments, the third subsystem is a buoyancy-based sodium metal storage and handling system. Petroleum or silicone oils with density intermediate between that of solid sodium (>0.95 g / cm3) when below the melting point of 98°C and greater than that of liquid sodium above the melting point (<0.93 g / cm3) will store the solid metal safely under oil while floating the liquid metal for refilling of Na-air modules, in accordance with some embodiments. In certain cases, these three subsystems may be spatially co-located or located separately and may be operated simultaneously or at different times. Each subsystem may further comprise additional subsystems, in some cases.

[0340] In some embodiments, the proposed technology may provide electrical storage with high gravimetric or volumetric energy density and high continuous or pulse power at affordable cost. For example, in certain embodiments, the proposed technology may provide electrical storage with breakthrough energy density and high pulse power at affordable cost. In some embodiments, sodium metal as an energy carrier in the Na-air cell format may provide for widespread electrification of difficult-to-decarbonize transportation sectors including but not limited to aviation, locomotion, maritime shipping, and long-haul trucking. The technology has the potential to deliver a large reduction in greenhouse gas emissions from different modes of

[0341] #14431536vl transportation, in some cases. The proposed fuel cell system also has potential applications beyond transportation, including stationary or mobile storage for a wide variety of applications including commercial and industrial, data centers, residential, military, and disaster relief, or temporary field operations, in certain instances. For example, the proposed fuel cell system also has potential applications beyond transportation, including stationary or mobile storage for a wide variety of applications including commercial and industrial, data centers, residential, military, and disaster relief, in certain instances.

[0342] In accordance with some embodiments, innovations in the proposed technology include:

[0343] • Use of sodium metal as a transportable flowable high energy density energy carrier;

[0344] • A fuel cell designed to use a liquid metal as the fuel, have a removable discharge product, and valorize the discharge product (e.g., a fuel cell designed to use a liquid metal as the fuel, have a removable solid discharge product, and valorize the discharge product);

[0345] • Simple refueling of discharged cells with a single consumable (e.g., Na metal);

[0346] • Novel solid-electrolyte cell for Na metal production from feedstocks comprising NaCl operating at low overpotential (-4.5V cell) and simultaneously purifying feedstock (e.g., novel solid-electrolyte cell for Na metal production from NaCl operating at low overpotential (-4.5V cell) and simultaneously purifying feedstock); and / or

[0347] • Novel buoyancy-based systems to store solid Na metal safely under oil as a solid and to deliver it as liquid Na metal at modest temperature (~100°C).

[0348] In some instances, the proposed Na-air cell has higher energy density at ambient pressure (1600 Wh / L) than does compressed hydrogen at 690 bar and 15°C (1250 Wh / L).

[0349] The Ragone curve in FIG. 31 provides power and energy metrics, based on a cell model that includes temperature-dependent cell voltage and solid electrolyte conductivity, cathode overpotential, and masses of Na metal, solid electrolyte, air cathode, and endplates in accordance with some embodiments. The Ragone curve is then obtained by varying the current density, in some instances. In some embodiments, for the parameters given in the FIG. 31 legend, a specific power of 500 W / kg requires a current density of 334 mA / cm2and a specific power of 1500 W / kg requires 1.1 A / cm2. At these current densities, the corresponding specific energy exceeds 1000 Wh / kg by 40-55%, in some cases. For example, at these current densities, the

[0350] #14431536vl corresponding specific energy exceeds the minimum 1000 Wh / kg by 40-55%, in some cases.

[0351] This model is an optimization tool for cell design, in some embodiments. See Table 1.

[0352] Table 1. Proposed Target (in accordance with some embodiments) and FOA Category A for Various Parameters

[0353] In one embodiment, the disclosed sodium-air cell features a refillable sodium metal anode and a removable discharge product. In some embodiments, the sodium-air cell comprises a Na-ion conducting solid electrolyte with high ionic conductivity and stability against sodium in the operating temperature range of -50°C to 200°C, which comprises temperatures where the metal comprising the electrode may be solid or liquid. For example, sodium metal has a melting temperature of about 98 °C at 1 atm pressure. In another embodiment, said sodium-air cell comprises a gas cathode from which the discharge product (a sodium oxide / hydroxide / carbonate) can be removed. These components may be assembled into a unit that meets desired energy density and power metrics, in accordance with certain embodiments.

[0354] #14431536vl In another embodiment, low-cost materials are used for the current collectors and housing of the refuelable sodium- air cell.

[0355] Achieving 1000 Wh / kg in the sodium-air battery is possible utilizing a sodium thickness of about 10 mm corresponding to an areal capacity of ~lAh / cm2, producing an equivalent discharge product thickness of ~2 cm (at 50% solids packing density), in some cases. For example, achieving 1000 Wh / kg in the sodium-air battery requires utilizing a sodium thickness of ~10 mm corresponding to an areal capacity of ~lAh / cm2, and an equivalent discharge product thickness of ~2 cm (at 50% solids packing density), in some cases. Concurrently, to achieve, e.g., 500 W / kg continuous power requires a current density of 0.3A / cm2, in certain instances. To achieve 18s peak power of 1500 W / kg requires a current density of ~lA / cm2, in some instances. This duration is short enough that discharge product removal is probably not necessary during that step, in certain cases. For example, this duration is short enough that discharge product removal during the peak power pulse is not necessary, in certain cases. According to some embodiments, the sodium metal-solid electrolyte interface has adequately fast transport for these requirements. For example, according to certain embodiments, the sodium metal-solid electrolyte interface is selected to have adequately fast transport for these requirements. In accordance with certain embodiments, liquid sodium used with P” alumina has stripping capacities >10Ah / cm2at 1 A / cm2and used with NaSICON has stripping capacity of at least 10Ah / cm2at 0.1 A / cm2. In some embodiments, continuous sodium stripping is demonstrated at >100mA / cm2for >lAh / cm2at 100-200°C with an average overpotential <0.2V, excluding separator resistance, in a symmetric cell format.

[0356] According to some embodiments, at the air cathode, Na-air cells have three possible discharge sodium oxide products each resulting in a characteristic operating voltage - Na2<3 (Eceii = 1.95V), Na2<D2 (Eceii = 2.33V), and NaCh (Eceii = 2.27V). While each can meet the energy density goals, in certain embodiments, sodium peroxide is most commonly formed. In some embodiments, candidate solid electrolytes include Na P”-alumina and NaSICON, both of which have conductivity > 10'2S / cm at 100°C and are available commercially. For example, in some embodiments, candidate solid electrolytes include Na P”-alumina and NaSICON, both of which have conductivity > 10'2S / cm at 100°C and are sold commercially.

[0357] In some embodiments, unlike rechargeable metal-air batteries, the gas cathode does not need to store the discharge product, thereby reducing the need for porous gas diffusion electrodes of large thickness. In certain embodiments, unlike rechargeable metal-air, the cathode

[0358] #14431536vl does not need to store the discharge product, thereby eliminating the need for thick, porous gas diffusion electrodes. In some cases, a 2-dimensional cathode that is adherent to the solid electrolyte may be used, including metal or carbon films, sintered cermets, or mixed ionic- electronic conductors (MIEC). In certain instances, cathodes that are only electronically conductive will form NaxOyat the three-phase boundary between the solid electrolyte, conductor, and gas phase, while MIECs can form NaxOyat their surface as well. According to some embodiments, cathodes comprise continuous and patterned cathodes of both types, using materials including but not limited to noble metals, lanthanum strontium manganate (LSRM) and mixed ionic-electronic conductors (MIECs) such as NaCoCE, sodium polyanionic compounds that are the sodiated analogs of lithium transition metal phosphates such as LiFePCE and LiMnPCU, and Na-NMCs, which are sodium-substituted analogs of lithium battery cathode compounds such as LiCoCE and lithiated nickel-manganese-cobalt (NMC) compounds such as NMC1 11, NMC523, and NMC811, the numbers referring to the relative proportions of Ni, Mn and Co. According to some embodiments, cathodes comprise continuous and patterned cathodes of both types, using materials such as noble metals, lanthanum strontium manganate (LSRM) and mixed ionic-electronic conductors (MIECs) such as NaCoCE and Na-NMCs, which are sodium-substituted analogs of lithium battery cathode compounds such as LiCoCE and lithiated nickel-manganese-cobalt (NMC) compounds such as NMC111, NMC523, and NMC811, the numbers referring to the relative proportions of Ni, Mn and Co. According to certain embodiments of the disclosure herein, sodium-conducting MIECs may comprise any sodium-ion battery active electrode compound or its derivative, or any sodium-metal battery cathode or its derivative.

[0359] According to some embodiments of the invention, the gas composition may be controlled to obtain desired NaxOydischarge products or related hydroxides and / or carbonates. For example, in some instances, water vapor in the gas stream may cause the formation of NaOH or NaOH dissolved in aqueous solution, and carbon dioxide in the gas stream may cause formation of sodium carbonate or bicarbonate. In certain cases, removal of the discharge product may also comprise control of gas flow velocity or flow patterns. Control of the discharge product and its removal may maximize power as well as energy of the sodium-air fuel cell, in accordance with certain embodiments.

[0360] Some embodiments of the invention comprise a solid-electrolyte molten salt electrolysis cell for the production of Na metal and Ch gas. Currently, sodium metal may be produced

[0361] #14431536vl electrolytically in a Downs cell (FIG. 34A), from a NaCl-CaCh eutectic melt in which the overall cell reaction is 2NaCl(i) — 2Na<i) + Ch(g). Addition of calcium chloride allows a decrease in the operating temperature of such a cell to -590 °C. Both positive and negative electrodes are in contact with the molten salt, and density differences are used to separate the molten salt, sodium metal, and chlorine gas. Any impurities in the melt with a greater reduction potential than sodium or oxidation potential than chlorine can contaminate the products, so the incoming salts need to be of high purity. And, despite having a lower reduction potential than sodium, calcium contaminates the sodium to -1% concentration, requiring further purification. These additional process steps contribute to cost, such that Na metal sells for $2-3 / kg-Na despite the electrical energy consumption being only $0.50 / kg-Na (7.1V cell, $0.05 / kWh electricity price). For example, these additional process steps contribute to cost, such that Na metal sells for ~$3 / kg-Na despite the electrical energy consumption being only $0.50 / kg-Na (7.1V cell, $0.05 / kWh electricity price).

[0362] Instead, in accordance with some embodiments, an advantageous electrolytic cell configuration uses a solid-state, largely single-ion conductor to separate the molten salt mixture from the liquid sodium (FIG. 34B). For example, instead, in accordance with some embodiments, an advantageous electrolytic cell configuration uses a solid-state, single-ion conductor to separate the molten salt mixture from the liquid sodium (FIG. 34B). This simultaneously reduces the purity requirement for the incoming salt and removes the need for post-electrolysis purification, in some cases. In certain embodiments, a broader pool of molten salt mixtures becomes usable, including cations with greater reduction potentials than sodium and lower melting point than NaCl-CaCh. At high current density, using NaCl-AlCh with a Na- ?” alumina separator and producing high-purity sodium at 300 °C, an anode reaction AlCLf — AlCh + Vi Ch + e’ may result in the deposition of aluminum chloride, fouling the graphite electrode. According to some embodiments of the invention, such potential issues are mitigated with temperature and salt composition control (i.e., operating with NaCl-rich liquid) and active convection, amongst other enhancements. In some embodiments, the operating voltage is accordingly reduced from 7.1V to 4.5V (IV overpotential), where the electricity cost to produce Na metal is $0.29 / kg-Na and the LCOS reaches $0.18 / kWh.

[0363] In some embodiments, a buoyancy-based approach for safe storage, handling, and delivery of sodium metal comprises the use of petroleum or silicone oils with density in between that of solid and liquid sodium as a storage medium. Accordingly, in certain embodiments, solid

[0364] #14431536vl sodium will remain safely immersed, but upon warming to above the sodium melting point (98 °C), the solid sodium melts to form liquid sodium that floats on the oil and may be delivered to a container or transport mechanism that supplies the sodium-air fuel cell.

[0365] Additional embodiments and examples:

[0366] Battery components and design according to some embodiments:

[0367] • A cell comprising a sodium metal anode (liquid or solid), a Na-ion conducting electrolyte, and a gas electrode, in some embodiments. Examples of gas electrodes include metal or carbon films, sintered cermets, or mixed ionic-electronic conductors (MIEC), in certain cases. A cell comprising a sodium metal anode (liquid or solid), a Na-ion conducting electrolyte, and an air electrode, in some embodiments. Examples of air electrodes include metal or carbon films, sintered cermets, or mixed ionic-electronic conductors (MIEC), in certain cases. o In some instances, metals include Au, Pt, Fe, Cu, Ni, Sn, Mo, Cr, Ti. o In certain embodiments, metal and carbon films can be deposited by the following methods (sputtering, screen-printing, controlled vapor deposition, evaporation, electroplating). The films can be conformal or heterogeneous, (i.e. grids achieved via screen -printing), according to some embodiments. o In some cases, cermet refers to a composite material consisting of an electronic conductor and an ionic conductor. In certain embodiments, the Na-ion conductor can comprise the following: (Na beta-alumina, NaSICON). In some embodiments, the electronic conductor could be a metal (Fe, V, Cr, Zr, Ni, Cu, Al, Sn), an electronically conductive oxide ( FC3O4, Lai-xSrxMnO3), or other conductors (carbon black, graphite). o In certain embodiments, mixed-ionic-electronic conductors include Na-ion cathodes (NaCrCE, Nao.vCoCh, Nao.44Mn02, Nao.vMnCh, NaCoPCE, NaNiPCU, NaFePCE, NaMnPCU, Prussian blue, Prussian white). o According to some embodiments, cermets and MIECs are deposited onto the electrolyte by any of the following methods (spray-casting, drop-casting, screenprinting, tape-casting, sputtering). In certain instances, binders including PVDF, PEO... (e.g., PVDF or PEO) can be added to the mixture to improve adhesion. Deposited films can be sintered, with and without the use of a press, in accordance with some embodiments.

[0368] #14431536vl o In certain cases, surface-treated Na-ion electrolytes can also be an MIEC (oxygen-deficient Na beta alumina, transition-metal doped Na-ion conductors).

[0369] • Cell fixture design: o In some embodiments, single cell design comprises a sodium metal anode (liquid or solid), a Na-ion conducting electrolyte in the form of a tray to house sodium metal, and an air electrode sandwiched between a perforated current collector which allows for air flow, which can be stacked to increase voltage (through series connections of the cells) and / or capacity (through parallel connections of the cells). o In certain cases, the thickness dimensions of the components to reach lOOOWh / kg are 0.5mm for the electrolyte, 0.6mm for the end plates, and 10mm for the sodium.

[0370] In accordance with some embodiments, a sodium-gas test cell is shown in FIGs. 37A- 37C.

[0371] Non-limiting embodiments of the oxygen / air electrode are shown in FIG. 33C.

[0372] In some embodiments, the gas stream for the sodium-air cell (see FIGs. 37A-37C) comprises oxygen and water. FIGs. 38, 36A, 36B, 39, and 40 show that a gas stream that is humidified changes the composition and structure of the discharge product, facilitating its removal and improving the discharge performance of the cell. As shown in FIG. 38, lower overpotential was observed upon switching from dry, static O2 gas at the cathode to 100% humidity, flowing (30ml / min) O2.

[0373] As shown in FIGs. 36A and 36B, different discharge products were observed when comparing inlet gas streams of dry O2 vs. 100% humidity O2. In dry O2, the x-ray diffraction pattern initially showed NaOH phase, but evolved to a pattern with almost no detectable crystalline peaks within 4 minutes, showing the formation of a liquid solution from the crystalline NaOH. Within 1 hour, crystalline Na2CO3-H2O formed, illustrating capture of carbon dioxide from ambient air. In FIG. 36B, the data labeled “after discharge” was obtained from the cathode after the cell was subjected to a current density of 0.5mA / cm2, and reached a charge capacity of 4.89 mAh / cm2, at 100’C in static O2 atmosphere. The data labeled “after discharge, exposure in air” was obtained under the conditions 0.2mA / cm2, 8.3 mAh / cm2, 50°C, static O2. In the experiments in FIG. 36B, 7 pm of NaOH formed per ImAh / cm2of capacity.

[0374] #14431536vl As shown in X-ray diffraction patterns in FIG. 39, different discharge products were observed for inlet gas streams of dry O2 vs. 100% humidity O2. In the latter case, NaOH-FhO discharge product evolved to Na2CO3 within 30 minutes, showing that carbon dioxide was captured from the ambient air.

[0375] FIG. 40 shows scanning electron microscope images of the discharge product at different stages of evolution, showing that it is possible to control the morphology of the discharge product by varying humidity, in accordance with some embodiments.

[0376] In some embodiments, the gas electrode for the sodium-air cell comprises a mixed ionic- electronic conductor (MIEC). In some embodiments, the ionic conduction is of oxygen ions. FIGs. 41-50 illustrate specific compositions and embodiments of the MIEC and its beneficial use, in accordance with some embodiments.

[0377] FIG. 41 shows design principles for an MIEC-based oxygen / air electrode, according to some embodiments.

[0378] FIG. 42 shows cathode materials for sodium-air fuel cells, in accordance with some embodiments. In some embodiments, the MIEC comprises Nao.?Mn02, Nao.44Mn02, Nao.?Co02, NaNiFeMnO2, or NaNio.5Mn1.5O4. In certain embodiments, Nao.?Mn02 can be used as MIEC.

[0379] FIG. 43 shows a process of making an MIEC cathode and building a cell, in accordance with some embodiments.

[0380] FIGs. 44A-44B show electrochemical test results for Na-air fuel cell with an MIEC cathode comprising a composite of Nao.?Mn02 / Super P Carbon / PVDF, in accordance with some embodiments. Both FIG. 44A and FIG. 44B showed initial OCV at 2.4 V followed by a plateau at 2.33 V. The formation of NaxOy occurred at 2.33 V.

[0381] FIG. 45 shows SEM images of the top surface of an MIEC electrode before and after discharging of the sodium-air fuel cell, in which the needle morphology after discharging showed the formation of a discharge product and the elemental analysis of the surface before and after discharge showed an enrichment of Na relative to Mn.

[0382] FIGs. 46A-46B show cross-sectional SEM images and elemental maps confirming the formation of a NaxOylayer on the electrode after discharging.

[0383] FIGs. 47A-47B show Raman spectra confirming Na2CO3 formation in the discharge product after air exposure.

[0384] FIG. 48 shows a cermet design for an MIEC cathode comprising a solid electrolyte phase to provide ionic conductivity and a metallic phase to provide electronic conductivity.

[0385] #14431536vl FIG. 49 shows a process for making a cermet electrode, in accordance with some embodiments. In some embodiments, the metallic phase comprises Fe, Cr, V, Zr, W, or Mo.

[0386] FIG. 50 shows an MIEC cermet cathode comprising vanadium metal and sodium |3” alumina applied to a solid electrolyte sheet.

[0387] The following examples are intended to illustrate certain embodiments of the present invention, but does not exemplify the full scope of the invention.

[0388] EXAMPLE 1

[0389] This example demonstrates the extraction of copper (Cu) from copper (II) sulfide (CuS) through the method of sodium reduction at a relatively low temperature of approximately 300°C, followed by the separation of Cu from other reaction products, namely sodium sulfide (Na2S), through aqueous means. Electrorefining of the separated solid mixture composed predominantly of Cu by mass was demonstrated. This method may also apply to the extraction and separation of Cu from mineral feedstocks of lower purities than the present sample materials. Mineral feedstocks include but are not limited to chalcopyrite (CuFeS2).

[0390] In this example, Na metal reduced Cu2+in CuS to Cu° (Cu metal), producing Na2S as a second reaction product through the spontaneous, exothermic displacement reaction:

[0391] 3 Na (1) + CuS (s) Cu (s) + Na2S (s) + Na (1) (Eq. 12)

[0392] Here, an excess of Na over what is strictly necessary to react the CuS was used. FIG. 5 shows the Na-Cu-S ternary phase diagram and the location of the target composition. The target composition lies inside a compatibility triangle at 25 °C - a three-phase co-existence region - where Na, Na2S, and Cu co-exist at equilibrium. This region of the phase diagram has no ternary compounds.

[0393] Samples were prepared as follows. In an argon-filled glovebox, sodium metal (99.9% trace metals basis, cubes in mineral oil; Source: Sigma Aldrich) was first rolled into a flat sheet. CuS (powder; Source: Fisher Scientific) which had undergone high-energy ball milling in a stainless- steel jar with zirconia milling media for approximately one hour to reduce its particle size, was integrated into the Na metal through a rolling and folding process. CuS powder was spread across a section of a Na metal sheet, which was then folded over the powder and rolled and flattened. This procedure was repeated several times until all powder was mechanically mixed into the metal. A typical batch size comprised 0.79 g of Na metal and 1.10 g of CuS powder. The mechanically mixed sample was placed in a quartz ampule, evacuated to a pressure

[0394] #14431536vl of approximately 6 mbar, sealed by melting the quartz with an oxy-acetylene torch, and heat- treated inside a muffle furnace. Although the reaction between Na and CuS is spontaneous even at room temperature (Gibbs free energy of -311 kJ per mole of Cu produced), the sample was placed in a furnace held at 300°C to accelerate the reaction. Throughout Examples 1-9, it should be understood that the heat of reaction heated the sample to a higher temperature than the furnace temperature. A homogenous, powdered mixture of Cu, Na2S, and Na was obtained after heating for 3 hours at 300°C.

[0395] The reacted sample was ground using a mortar and pestle and loaded into an air-free sample holder (Source: Anton Paar) for X-ray diffraction (XRD) (using Cu K-alpha radiation, wavelength -1.54 A). Rietveld refinement analysis was conducted to identify the phase fractions. FIG. 6 shows the XRD spectrum where the major peaks are attributable to Cu, Na2S, and Na. FIG. 7 compares the expected molar ratio of Cu, Na2S, and Na based on the equilibrium phase diagram with the experimental results. The phase percentages calculated from the phase diagram are 33 mol % each of Cu, Na2S, and Na. The measured values were 38 mol% Cu, 39 mol% Na2S, and 22 mol% Na, with trace amounts of CU1.75S. The difference between expected and actual mole fractions is attributed to the transport of Na inside the ampule by vaporization from the sample, resulting in higher relative mole percentages of Cu and Na2S.

[0396] Cu was separated from Na2S and Na by adding 30 mF of de-aerated deionized (DI) water to 0.80g of the sample, dissolving the Na2S and reacting the Na with water to form dissolved NaOH and H2 gas. The sample was held under argon during this procedure to avoid oxidizing the Cu, which the Cu Pourbaix diagram (FIG. 8) shows is favored at high pH. In other embodiments, non-oxidizing gas ambients such as those comprising nitrogen may also be used. The sample was centrifuged at 5000 rpm for 15 minutes and the supernatant fluid was decanted. Sodium metal may be recovered from this solution following the procedure described in Example 9. The remaining solid was washed with de-aerated DI water, and dried in a vacuum oven at 80°C overnight. XRD and Rietveld refinement analysis showed that this solid consists of 75 wt. % Cu, 16 wt. % Cu2S, and 9.1 wt. % CU2O (FIG. 9). Sodium metal may be recovered from the Na2S solution using an electrolytic cell similar to the one described in Example 9.

[0397] Electrorefining of the copper-enriched sample was then demonstrated. The dried sample had the shape of a small ingot. Electrorefining was performed in a glass beaker, where the copper sample served as the anode and reference electrode and a graphite rod (0.25 inch diameter; Source: McMaster-Carr) served as the cathode. The Cu ingot was held with a tantalum

[0398] #14431536vl wire (0.6 mm diameter; Source: MSE supplies). The electrolyte was an aqueous solution containing 0.80M copper sulfate (CuSCU) (>99% purity, Source: Sigma Aldrich) and 0.46M sulfuric acid (H2SO4) (95.0-98.0%, Source: Sigma Aldrich). Tantalum was selected as the anode lead and current collector because it does not react with or dissolve in H2SO4, and other such materials may also be used. A constant current density of 20 mA / cm2was applied to the electrochemical cell until a decline in cell voltage was observed. Copper was observed to have been plated on the graphite rod, as shown in FIG. 10, demonstrating electrorefining of the copper ingot obtained from the starting CuS.

[0399] The Na-Cu-S ternary phase diagram (FIG. 5) shows that two-phase co-existence of Cu and Na2S may occur near the melting point of sodium. Accordingly, in some embodiments, the reaction between Na and CuS may be conducted without an excess of sodium metal:

[0400] 2 Na (1) + CuS (s) Cu (s) + Na2S (s) (Eq. 13)

[0401] EXAMPLE 2

[0402] This example demonstrates the extraction of zinc (Zn) from zinc (II) sulfide (ZnS) (or sphalerite) at a relatively low furnace temperature of 485°C using sodium (Na) reduction, followed by aqueous separation as discussed in Example 1. The heat of reaction is understood to elevate the reaction temperature above that set by the furnace. This method may be applied to the extraction and separation of Zn from mineral feedstocks of lower purity than the present sample materials.

[0403] In this example, Na metal reduced Zn2+in ZnS to Zn° (metallic Zn metal), producing sodium sulfide (Na2S) as a second reaction product through the spontaneous, exothermic reaction:

[0404] 2 Na (1) + ZnS (s) Zn (s) + Na2S (s) (Eq. 14)

[0405] The change in Gibbs free energy and enthalpy of reaction at 25°C are -160 kJ / mole and -165 kJ / mole of Zn produced, respectively. FIG. 11 shows the Na-Zn-S ternary phase diagram at 25°C and the location of the target composition. The target composition lies on a two-phase coexistence line where Zn and Na2S co-exist at equilibrium. This region of the phase diagram has no ternary compounds. A typical batch size comprised 0.70 g ZnS powder (99.99% purity; Source: Fisher Scientific) and 0.33 g of Na metal (99.9% trace metals basis, cubes in mineral oil; Source: Sigma Aldrich). Sample preparation occurred through the same rolling and folding method described in Example 1. The sample was subsequently placed in a quartz ampule,

[0406] #14431536vl evacuated to a pressure of approximately 6 mbar, sealed by melting the quartz with an oxyacetylene torch, and heat-treated inside a muffle furnace.

[0407] The Na-Zn binary (FIG. 12) and ternary phase diagrams indicate that NaZn - an intermetallic compound that is 93 mol % Zn - may result. Therefore, the sample was treated at a temperature beyond the melting point of Zn (419.5°C) to allow NaZn to decompose and form Zn metal upon cooling. FIG. 13 compares the composition of the resulting homogenous, powdered mixture of 34 mol % Zn and 66 mol % Na2S obtained after three hours at 485°C with the expected composition of 50 mol % Zn and Na2S, respectively. The difference between expected and actual mole fractions may be attributed to the transport of Zn inside the ampule by vaporization from the sample and condensation elsewhere. FIG. 14 shows the corresponding XRD spectrum, where Zn and Na2S account for all major peaks. In other embodiments, any temperature above the melting point of Zn may destabilize the NaZn intermetallic such that Zn metal forms upon cooling.

[0408] Zn may be separated from Na2S through the same aqueous procedures described in Example 1. The Zn Pourbaix diagram (FIG. 15) shows that Zn oxidation is favored to occur at all pH at room temperature, wherein the Zn stability region resides below the hydrogen evolution line, leading to the following reaction:

[0409] Zn (s) + H2O (1) ZnO (s) + H2(g) (Eq. 15)

[0410] The formation of a ZnO or Zn(OH)2 passivation layer may prevent significant amounts of Zn from reacting with water. The passivation layer, in combination with potentially slow reaction rates, allowed for the separation of Zn from Na2S in an aqueous environment. FIG. 16 shows that the resulting solid mixture after centrifugation and washing consists of 97.7 mol% Zn and 2.3 mol% ZnO determined by XRD and Rietveld refinement. Reduction of the oxygen content of the solid mixture may be accomplished through heating in a reducing atmosphere such as one containing hydrogen or carbon monoxide gas or an inert atmosphere such as nitrogen or argon. Sodium metal may be recovered from the Na2S solution using an electrolytic cell similar to the one described in Example 9.

[0411] The relatively low melting point of Zn compared to various other metals may allow for a non-aqueous separation method, whereby Na2S (density: 1.86 g / cm3) may float to the top of molten Zn (density at melting point: 6.57 g / cm3) as a slag layer. The Na2S layer may be physically removed from the top, the Zn metal drained from the bottom as a meltor upon cooling, Na2S and Zn may solidify into two layers, which can be mechanically separated. The

[0412] #14431536vl Zn mixture can also be electro-refined using a similar process described in Example 1 with an electrolyte containing a Zn salt.

[0413] EXAMPLE 3

[0414] This example demonstrates the extraction of tungsten (W) from tungsten (IV) disulfide (WS2) through sodium (Na) reduction at a relatively low furnace temperature of 600°C, with a reaction temperature that is higher due to the heat of reaction, followed by the separation of W from other reaction products, namely sodium sulfide (Na2S), through the aqueous method described in Examples 1 and 2. This method may apply to the extraction and separation of W from sulfide mineral feedstocks of lower purity than the present sample materials.

[0415] In this example, Na metal reduced W4+in WS2 to W° (metallic W metal), producing sodium sulfide (Na2S) as a second reaction product through the spontaneous, exothermic displacement reaction:

[0416] 4 Na (1) + WS2(s) W (s) + 2 Na2S (s) (Eq. 16)

[0417] The change in Gibbs free energy and enthalpy of reaction at 25°C is -470 kJ / mole and -481 kJ / mole of W produced, respectively. FIG. 17 shows the Na-W-S ternary phase diagram at 25 °C and the location of the target composition. The target composition lies on a two-phase coexistence line where W and Na2S co-exist at equilibrium. This region of the phase diagram has no ternary compounds. A typical batch size comprised 0.70g WS2 powder (99% purity; Source: Sigma Aldrich) and 0.26 g of Na metal (99.9% trace metals basis, cubes in mineral oil; Source: Sigma Aldrich). A mortar and pestle were used to mix the starting Na metal and WS2 powder. The sample was subsequently placed in a quartz ampule, evacuated to a pressure of approximately 6 mbar, sealed by melting the quartz with an oxy-acetylene torch, and heat- treated inside a muffle furnace.

[0418] FIG. 18 compares the composition of the resulting homogenous, powdered mixture after heating for six hours in the furnace held at 600 °C, determined by X-ray diffraction (XRD) to have 29 mol% W and 71 mol% Na2S, with the expected composition of 33 mol % W and 67 mol % Na2S. A thermocouple wrapped around the ampule detected an exotherm near 180°C, wherein the temperature increased by approximately 100°C before cooling to the set furnace temperature, indicating that the reaction heat assisted in the reaction. In a subesequent experiment, the reactants were cooled to room temperature immediately after the exotherm. This sample was determined by XRD to consist of 25 mol % W, 68 mol % Na2S, and 7 mol % Na, which closely resembles the composition after treatment at 600°C for six hours (FIG. 19).

[0419] #14431536vl Therefore, it was shown that the extended heat treatment at 600°C for six hours was not necessary to obtain the desired reaction products, and that lower temperatures and / or shorter times may be used. FIG. 20 compares the XRD spectra of the two samples that underwent different temperature treatments and shows that W and Na2S account for most major peaks. The similar product compositions indicate that Na reduction of WS2 occurs almost instantaneously at temperatures as low as 180°C. In some cases a higher reaction temperature, e.g., 600°C or above, may be preferred to transform the metastable -W phase to a-W.

[0420] The W Pourbaix diagram (FIG. 21) shows that W oxidation is favored at all pH at room temperature. However, the W stability region lies just below the hydrogen evolution line, which, combined with slow reaction rates as is the case with zinc in Example 2 may avoid the oxidation reaction:

[0421] W (s) + 3 H2O (1) WO3(s) + 3 H2(g) (Eq. 17)

[0422] Aqueous separation of W from Na2S as described in Example 1 was pursued, and the resulting solid mixture after centrifugation and washing contained 98 mol % W with some minor impurities (FIG. 22). Reduction of the oxygen content of the solid mixture may be accomplished through heating in a reducing atmosphere such as one containing hydrogen or carbon monoxide gas or an inert atmosphere such as nitrogen or argon. Sodium metal may be recovered from the resulting Na2S solution using an electrolytic cell similar to the one described in Example 9. In some embodiments, W may be separated from Na2S without centrifugation, relying solely on gravitational forces due to the high density of W (19.3 g / cm3).

[0423] EXAMPLE 4

[0424] This example demonstrates the extraction of tungsten (W) from calcium tungstate (CaWO4), also known as scheelite, through sodium (Na) reduction at a relatively low furnace temperature of approximately 500 °C, in which the reaction temperature may be elevated using the heat of reaction, followed by the separation of W from other reaction products through the aqueous method described in the above examples. This method may also be applied for the extraction and separation of W from oxide mineral feedstocks of lower purity than the present sample materials. The methods of this example may also be applied to extract tungsten from (Fe, Mn)W04, also known as wolframite. Sodium reduction of CaWO4 occurs through the following spontaneous, exothermic reaction:

[0425] 6 Na (1) + CaWO4(s) W (s) + CaO (s) + 3 Na2O (s) (Eq. 18)

[0426] #14431536vl This reaction has a standard Gibbs free energy change and enthalpy change at 25°C of -202 kJ / mole and -244 kJ / mole of W produced, respectively. FIG. 23, which was produced using the FactSage thermodynamics modeling software, shows the onset of stability for the phases sodium tungstate (Na2WO4) and Na at temperatures above 600 °C, indicating that the reaction should be conducted below this approximate temperature, but at a temperature above room temperature, whether due to self-heat from the reaction or externally supplied heating or cooling. A typical batch size comprised 0.50 g CaWO4 powder (Source: Sigma Aldrich) and 0.24 g of Na metal (99.9% trace metals basis, cubes in mineral oil; Source: Sigma Aldrich). Sample preparation occurred through the same rolling and folding method described in Example 2. The sample was subsequently placed in a quartz ampule, evacuated to a pressure of approximately 6 mbar, sealed by melting the quartz with an oxy-acetylene torch, and heat-treated inside a muffle furnace at 500 °C for 10 hours. The product was determined to be 4 mol% W and 96 mol% CaO by XRD and Rietveld refinement (FIG. 24). Na2O was not detected as a crystalline phase, likely due to its rapid reaction with atmospheric water upon exposure of the sample to air. The broad XRD peaks indicate that the W and CaO crystallites are on the scale of 1 to 10 nm, which was corroborated by size-strain analysis conducted using the full width half maximum (FWHM) of each peak in the XRD pattern and Williamson-Hall plots.

[0427] After reduction, tungsten was separated from CaO and sodium oxide(s) by adding water to form aqueous solutions comprising dissolved calcium hydroxide (Ca(OH)2) and sodium hydroxide (NaOH), NaOH and Ca(OH)2 have substantial solubility in water and have low densities compared to tungsten metal, allowing tungsten to be collected through density-based separation methods such as sedimentation and centrifugation, and / or by filtration of solid tungsten particles from solubilized sodium and calcium hydroxide. Ca(OH)2 may also be separated from NaOH by virtue of its lower aqueous solubility (e.g., 0.0016 g Ca(OH)2 / g H2O at 20 °C) compared to that of sodium hydroxide (e.g., 1.09 g NaOH / g H2O at 20 °C), as well as the pH-dependence of their respective aqueous solubilities, whereby NaOH has the higher solubility product constant and remains soluble at pH where Ca(OH)2 will precipitate. The product of aqueous separation in this experiment contained 20 mol% W and 80 mol% CaW04 (FIG. 24A). The appearance of CaW04 suggested tungsten dissolution as tungstate ions (WO42') in alkaline solution, which allows the re-forming of CaW04 according to the reaction:

[0428] Na2WO4(aq) + Ca(OH)2(aq) CaWO4(s) + NaOH (aq) (Eq. 19)

[0429] #14431536vl It is believed that the production of W as nanoscale particles facilitated the reaction with water forming WO42'. Without being bound by any particular scientific interpretation, it is believed that the extent of the reaction with water can be reduced by allowing the W forming reaction to take place at a higher temperature and / or longer time to coarsen the particle size of the W metal. Accordingly, in an embodiment, the reaction heat and reaction temperature were increased by incorporating an additional reactant with a large exothermic heat of reaction with the starting components. As one example, calcium chloride was used as such a reactant. The addition of calcium chloride (>97% purity; anhydrous CaCh; Source: Sigma Aldrich) as an additional reactant during sodium reduction of CaWC forms NaCl as shown in the reaction below and increases the adiabatic reaction temperature from 811 °C to 1,531 °C. Additive compounds used in the sodium reduction to alter the adiabatic reaction temperature are not limited to CaCh. However, it is advantageous to select compounds which result in the formation of water-soluble product compounds. In the present example, the NaCl produced in the case of CaCh addition is water-soluble, allowing aqueous dissolution and / or density-based separation of the W metal powder as described previously.

[0430] 6 Na (1) + CaW04(s) + 3 CaCh (s) W (s) + 4 CaO (s) + 6 NaCl (s) (Eq. 20) Compared to the reaction between Na metal and CaWCh alone, given by Eq. 18, this reaction increases the magnitude of the Gibbs free energy change and enthalpy change of the reaction in Eq. 18 to -935 kJ / mole and -975 kJ / mole per mole of W produced. This reaction was conducted at 550 °C for 10 hours in the same sealed ampule set up as described earlier, resulting in a product containing 5.9 mol% W, 44 mol% CaO, and 50 mol% NaCl (FIG. 24B). The heattreatment temperature and time described here are exemplary and one or both may be increased to further coarsen the W particles, or decreased in procedures where the total sample size is larger and allows for a higher self-heat temperature. In the present example, 30 mL of a 0.26 M hydrochloric acid (HC1) solution was used to fully dissolve the Ca(OH)2, allowing aqueous separation to obtain a final product composed of 83 mol% W and 17 mol% CaW04 (FIG. 24B). This is a 315% increase in the W purity of the final powder compared to the previously described experiment. Size-strain analysis of XRD peak widths revealed that W particles had coarsened as expected, from approximately 2 nm to 30 nm. Sodium metal may be recovered from the NaOH solution, for example, by using the electrolytic cell described in Example 9. Alternatively, the NaOH-bearing solution obtained after removal of W may be used to capture or sequester carbon dioxide. Ca(OH)2 can be separated from NaOH, for example, through the

[0431] #14431536vl control of temperature and / or pH, said Ca(0H)2 may be collected, for example using sedimentation and / or filtration.

[0432] EXAMPLE 5

[0433] In this prophetic example, tungsten metal is extracted from iron-rich wolframite (FeWC ) and / or manganese-rich wolframite (MnW04) by reaction with Na metal. The reduction reaction for extracting tungsten from FcWCU is as follows:

[0434] 2 Na (1) + FeWO4(s) Fe (s) + Na2WO4(s) (Eq. 21)

[0435] In the first step, such a reaction produces solid Fe and sodium tungstate (Na WCE). Sodium tungstate has a relatively high solubility in water (0.742 g / g H2O at 25 °C), and may be dissolved as an aqueous solution, allowing solid Fe particles formed in the sodium reduction reaction to be separated, for example, by density -based separation processes such as sedimentation or centrifugation, filtration, or magnetic separation. After removal of the iron, tungsten is obtained from the Na2WO4-enriched solution. For example, sodium tungstate may be reacted with diluted ammonia to form ammonium isopoly tungstate solutions, from which ammonium paratungstate (APT) may be crystallized and pyrolyzed to form tungsten (VI) oxide (WO3), which may subsequently be reduced with hydrogen gas to form W.

[0436] The Na2WO4 solution may also be reacted with solubilized or solid calcium hydroxide according to the reaction:

[0437] Na2WO4(aq) + Ca(OH)2(s) CaWO4(s) + 2 NaOH (aq) (Eq. 22) The solid CaWCU produced from the above reaction may be separated, collected, optionally dried, and reduced with Na metal to obtain W metal according to the previously described processes in which CaWCU is an input.

[0438] Tungsten extraction from manganese-rich wolframite (MnWCU) may also be performed using Na reduction, resulting in W, Na2O, and manganese oxide (MnO) as exemplified by the reaction:

[0439] 6 Na (1) + MnW04(s) W (s) + MnO (s) + 3 Na2O (s) (Eq. 23)

[0440] Upon the addition of water to the reacted mixture, the Na2O will dissolve, forming a NaOH solution, from which W and MnO may be separated. The W and MnO may subsequently be separated using various methods, including but not limited to density-based separation utilizing the higher density of tungsten, and / or selective dissolution of MnO in acid or base.

[0441] In the extraction of W from FeWO4 and MnW04, sodium metal can be recovered from the NaOH solutions through the electrolytic process described in Example 9 to establish a

[0442] #14431536vl closed-loop process, or the NaOH-bearing solutions may be used to capture and sequester carbon dioxide from the atmosphere or from a concentrated source such as the flue gas from a power plant, cement plant, ammonia plant, or other industrial process in which a carbon-bearing fuel is combusted.

[0443] EXAMPLE 6

[0444] This example demonstrates the production of ferrotungsten (FexWy) from calcium tungstate (CaWCE) and iron (III) oxide (Fe2O3), via sodium (Na) reduction at a relatively low furnace temperature of 600 °C, using the heat of reaction to further heat the sample. Calcium chloride (CaCh) was added, as described in Example 4, to achieve a single- step reaction with a sufficiently high adiabatic reaction temperature to form the desired alloy. This method may also be used to produce alloys of W and Fe from mineral feedstocks of lower purity than the present sample materials.

[0445] In this example, Na metal reduced W6+and Fe3+to W° (W metal) and Fe° (Fe metal), respectively, which subsequently mixed to form ferrotungsten alloys. This process is described by the following spontaneous, exothermic reaction, where the target W content in the Fe3W2 alloy is 69 wt.%:

[0446] 21 Na (1) + 2 CaW04(s) + 1.5 Fe2O3(s) + 10.5 CaCl2(s)

[0447] Fe3W2(s) + 12.5 CaO (s) + 21 NaCl (s) (Eq. 24) The change in Gibbs free energy and the enthalpy of reaction at 25°C are -3,595 kJ / mole and - 3,708 kJ / mole of Fe3W2 produced, respectively, with an adiabatic reaction temperature of 1,594 °C. For reference, Fe and W melt at 1,538 °C and 3,422 °C, respectively. At scale, the adiabatic reaction temperature is sufficient to melt Fe, thereby facilitating of its reaction with W to form an alloy. A typical batch size comprised 0.20g CaWCU powder (Source: Sigma Aldrich), 0.083g Fe2O3 powder (>96% purity; Source: Sigma Aldrich), 0.405g CaCh (anhydrous, >97% purity; Source: Sigma Aldrich), and 0.168g Na metal (99.9% trace metals basis, cubes in mineral oil; Source: Sigma Aldrich). The CaWCU, Fe2O3, and CaCh were mixed by hand using a mortar and pestle until homogeneous. These powders may also be ball-milled together to achieve uniform mixing. This powder mixture was subsequently incorporated into sodium metal using the same rolling and folding method described in preceding examples. The sample was subsequently placed in a quartz ampule, evacuated to a pressure of approximately 6 mbar, sealed by melting the quartz with an oxy-acetylene torch, and heat-treated inside a muffle furnace at 600 °C for 3 hours.

[0448] #14431536vl Results are shown in FIG. 24C, which includes the XRD spectrum (using a Cu target X- ray source) of the reacted sample with peaks corresponding to ferrotungsten alloys labeled in green squares and circles. After reaction the samples was determined by XRD to be composed of 2.7 mol% Feo.3Wo.7 (89 wt% W), 2.8 mol% Fe0.92W0.08 (22 wt% W), 2.1 mol% WO3, 57 mol% NaCl, and 32 mol% CaO. Separation of the ferrotungsten alloys from the other reaction products may be conducted using the aqueous separation methods described in preceding examples. This example demonstrates the feasibility of producing ferrotungsten alloys in a single-step Na reduction process. The reactant ratios and heat-treatment conditions may be varied to produce ferrotungsten having a target composition in the range 70-85 wt.% tungsten as is desirable for many industrial applications.

[0449] EXAMPLE 7

[0450] This prophetic example describes the process of producing tungsten carbide (WC) from calcium tungstate (CaWCU) and carbon black (C) via sodium (Na) reduction at relatively low furnace temperatures (< 1000 °C), using the heat of reaction to further heat the sample. This method may be applied to the carburization of W from mineral feedstocks of lower purity than the reactants used in this example.

[0451] In this example, Na metal is used to reduce W6+to W° (W metal), which then spontaneously reacts with C to form WC, sodium oxide (Na2O), and calcium oxide (CaO) via the reaction:

[0452] 6 Na (1) + CaW04(s) + C (s) WC (s) + 3 Na2O (s) + CaO (s) (Eq. 25)

[0453] The change in Gibbs free energy and the change in enthalpy of reaction at 25°C are -241 kJ / mole and -284 kJ / mole of WC produced, respectively, with an adiabatic reaction temperature of 818 °C. Although C is also a reductant, carbothermic reduction of CaWO4 is nonspontaneous at temperatures below 1000 °C. As demonstrated in Example 4, sodium reduction of CaW04 occurs in samples heated to approximately 500 °C to form W, CaO, and Na2O. Tungsten carburization forming WC is spontaneous and exothermic, with the change in Gibbs free energy and the change in enthalpy of reaction at 25 °C being -38 kJ / mol and -40 kJ / mol of WC, respectively. To combine the reactants homogenously for the reduction step, CaW04 and C powders are mixed with sodium metal using the procedures described in preceding Examples. CaW04 and C powder may also be first ball-milled together to improve homogeneity and reactivity. The mixed reactants may also be pelletized under pressure, for example by using a hydraulic press, to further improve contact and reduce kinetic barriers to reaction and

[0454] #14431536vl carburization. Since a higher adiabatic reaction temperature may be beneficial through selfheating of the reactants, calcium chloride (CaCl2) may be introduced as described in a preceding example, resulting in the following spontaneous, exothermic reaction:

[0455] 6 Na (1) + CaWO4(s) + C (s) + 3 CaCl2(s) WC (s) + 6 NaCl (s) + 4 CaO (s) (Eq. 26) With the addition of CaCl2in the molar ratios of this reaction, the adiabatic reaction temperature increases from 811 °C to 1,539 °C.

[0456] The chemical stability of WC in water allows for its separation from water-soluble coproducts using the same aqueous separation steps as described in preceding examples.

[0457] EXAMPLE 8

[0458] This example demonstrates the extraction of antimony (Sb) from antimony(III) trisulfide (86283) via sodium (Na) reduction at a relatively low temperature of 520 °C, followed by aqueous separation. This method may also be applied to the extraction and separation of Sb from mineral feedstocks of lower purity than the present sample materials.

[0459] In this example, Na metal was used to reduce Sb3+in Sb2S3 into Sb° (Sb metal), producing sodium sulfide (Na2S) as a second product through the following spontaneous, exothermic displacement reaction:

[0460] 6 Na (1) + Sb2S3(s) 2 Sb (s) + 3 Na2S (s) (Eq. 27)

[0461] The change in Gibbs free energy and enthalpy of reaction at 25°C is -438 kJ / mole and -453 kJ / mole of Sb produced, respectively. FIG. 24D shows the Na-Sb-S ternary phase diagram at 25°C and the location of the target composition, which lies on a two-phase co-existence line where Sb and Na2S co-exist at equilibrium. This region of the phase diagram has no ternary compounds. A typical batch size comprised 0.75g Sb2S3 powder (Source: Sigma Aldrich) and 0.305g Na metal (99.9% trace metals basis, cubes in mineral oil; Source: Sigma Aldrich). Sample preparation consisted of the same rolling and folding method described in previous examples to incorporate the Sb2S3 powder into the Na metal. The sample was subsequently placed in a quartz ampule, evacuated to a pressure of approximately 6 mbar, sealed by melting the quartz with an oxy-acetylene torch, and heat-treated in a muffle furnace.

[0462] The bar chart in FIG. 24D compares the composition of a mixture reacted for three hours at 520 °C, determined by X-ray diffraction to have 28 mol% Sb, 58 mol% Na2S, 11 mol% NaSb, and 1.3 mol% NasSbSs, with the expected composition of 40 mol% Sb and 60 mol% Na2S. The presence of minor amounts of NaSb and Na^ShSs phases is attributed to incomplete reaction at Na-rich and Na-poor areas in the sample. Separation of Sb from Na2S via aqueous methods as

[0463] #14431536vl described in above examples was pursued, and the resulting solid mixture after centrifugation and washing consists of -100% Sb as shown in FIG. 24E, which compares the XRD spectrum (obtained using a Mo x-ray source) of the sample after Na reduction aqueous separation. The post-separation sample shows only Sb peaks (labeled with green stars), indicating that Na^ShSs and NaSb both dissolved in the aqueous solution. Sodium metal may be recovered from the resulting Na2S solution using an electrolytic cell similar to that described in Example 6.

[0464] In some embodiments, a reduced heat-treatment duration and / or a lower external heat input may be employed, particularly at larger reaction volumes where the self-heating reaction can generate higher reaction temperatures.

[0465] EXAMPLE 9

[0466] This example describes electrolytic production of Na metal from aqueous NaOH solution.

[0467] In this example, an electrolytic NaOH- splitting reactor is demonstrated, which decomposes concentrated NaOH aqueous solutions to Na metal at a negative electrode, and water and oxygen at a positive electrode, at moderate temperatures below 200°C. An electrolyzer of such design may be used to convert the sodium oxide product of a reactive extraction reaction between sodium metal and a metal salt comprising metal oxide, back to sodium metal, such that the sodium metal may be beneficially reused in smelting, or for some other purpose.

[0468] A sodium hydroxide or a sodium hydroxide-water mixture may be obtained from sodium oxide in the reacted mixture upon reaction with water. In accordance with certain embodiments, the negative and positive electrodes are separated by a solid sodium ion conductor, thereby preventing contact or crossover of water or oxygen with the sodium metal. H-cell reactors as illustrated in FIG. 24 were fabricated. 1 / 16” silicone gaskets with adhesive backing (source: 3M) of 14 mm inner diameter and 28 mm outer diameter were laser cut and applied to the H-cell chambers (source: Adams & Chittenden). A nickel wire was spot welded to a platinum gauze (5 x 5 mm, source: Thermo Scientific) to form a working electrode (positive electrode). A layer of tin was sputtered onto a sodium P” -alumina (NBA) disc (1 mm thick, source: lonotec) to improve sodium wetting. An H-cell chamber, sodium ^’’-alumina disc, and another H-cell chamber were clamped together to form the assembly illustrated in FIG. 25. The platinum electrode was inserted into one H-cell chamber, which was filled with 3 mL sodium hydroxide

[0469] #14431536vl solution prepared from anhydrous sodium hydroxide and deionized water in a 50:50 or 30:70 weight ratio. The other chamber was filled with sodium metal, to which was contacted a nickel wire, forming the counter electrode (negative electrode). The temperature of the cell was raised to either 110 °C or 130 °C, at which temperatures both the sodium metal and the NaOH-water solutions are liquids. An electrochemical formation cycle was conducted, consisting of the passage of a current density of 1 mA / cm2(where the area is taken to be the planar area of the platinum gauze) for 5 minutes, followed by 5 minutes of rest during which an EIS scan was taken. In this experiment, the platinum mesh is the anode and the sodium metal is the cathode, driving an overall reaction 4 NaOH — 4 Na + 2 H2O + O2. Following the formation cycle, linear sweep voltammetry was conducted, starting from the open circuit voltage of the cell and increasing the voltage at a rate of 10 mV / s until the current density, which was simultaneously measured, reached 1 A / cm2(FIG. 26A). Subsequently, a stepped galvanostatic test was conducted in which the cell was subjected to 30 minutes of constant current and 5 minutes of rest, followed by an EIS scan. In the stepped galvanostatic test, the initial current density was 25 mA / cm2, and in each subsequent step the current density was increased by 25 mA / cm2, until a current density of 500 mA / cm2was reached (FIG. 26B). A cumulative mass of 2.253 g of sodium metal was produced during this experiment.

[0470] FIG. 27 shows results from said NaOH- splitting electrolyzer, plotted as current density (left vertical axis) and sodium metal production rate per unit area (right vertical axis) against cell voltage (horizontal axis). Also shown as horizontal axes at the top of the figure are scales for the energy consumed per kilogram of sodium metal produced, and the electricity cost per kilogram of sodium metal produced, the latter assuming an electricity rate of $0.05 / kWh. Curves are shown for both the linear sweep voltammetry (LSV) measurements and the stepped galvanostatic measurements, for which the final voltage of each charge is shown. Results for a 30:70 NaOH:water solution operating at a cell temperature of 110°C and for a 50:50 NaOH:water solution operating at 130°C are shown. Also shown are estimated resistance contributions for charge-transfer resistance alone and for the solid state electrolyte (SSE) resistance alone. Results are compared to a typical Downs cell, representing the industry state- of-art, for producing Na from NaCl at a temperature of about 580°C. The results show that sodium production is achieved at lower voltage, lower temperatures, and comparable current densities to the Downs cell.

[0471] #14431536vl It is understood from this example that a wide range of NaOH-water ratios and temperatures may be used in said electrolyzer. FIG. 28 shows the water-NaOH phase diagram, with temperature as the vertical axis and NaOH concentration as the horizontal axis. In some embodiments, the solution composition and temperature may be selected to be anywhere within the single-phase liquid field labeled “UNSATURATED SOLUTION”, or any field of the phase diagram where an NaOH bearing liquid labeled “SOLN” may be present. Accordingly, the temperature of the NaOH solution or of the electrolyzer may range from as low as -25 °C to as high as 325°C. In can be preferred in some embodiments, that said electrolyzer is operated at a temperature where said sodium-ion conducting solid electrolyte has an appreciable sodium ionic conductivity, preferably above about 1 mS / cm, in order to have a high current density and rate of sodium metal production at a low voltage, preferably in some embodiments below about 8 V. It can be preferable in some embodiments if said electrolyzer is operated at a temperature above the melting point of the sodium, in order to facilitate easier collection of said sodium, and below the boiling point of the NaOH-water solution, which for a pressure of 1 atm is indicated by the curve in EIG. 28 labeled “P = 1 atm”. In can be preferable in some embodiments if said NaOH- water solution used in said electrolyzer has a high NaOH concentration in order to decrease the volume of solution that is used, and to increase the conductivity of the solution. Accordingly, in some cases, it can be preferred for the operating temperature and NaOH concentration to be in a field in EIG. 28 shown as the shaded region, falling above about 98C and below the curve labeled “P = 1 atm”. As pressure, P, increases, said curve will move up and to the left, enlarging said field of operation that is preferred in some embodiments. Also, from PIG. 27, all else being equal, a higher sodium ionic conductivity will move the curve labeled “SSE ohmic” to the left, lowering the SSE ohmic resistance and allowing a higher current density at a lower voltage. Also, all else being equal, for a given anode, a higher surface area may lower the charge transfer resistance, moving the curve labeled “charge transfer” to the left and allowing a higher current density at a lower voltage.

[0472] EXAMPLE 10

[0473] A solid-electrolyte test cell (FIGs. 32A and 32B) was constructed with configuration (sequence of components from one side of the cell to the other): Na metal | Na P”-alumina | sputtered gold | 1 atm O2. An open circuit potential of -2.33V vs. Na / Na+was observed indicating that the main discharge product was Na2O2. An important finding was that even with a thin sputtered metal cathode, it was possible to induce formation of the discharge product on

[0474] #14431536vl the exterior of the cathode. FIG. 55A shows pulsed discharge curves at 25 and 50 °C where the latter reached 8 mAh / cm2. Cross-sections of such cells after cycling show cases where the Na2<32 discharge product formed between the gold layer and solid electrolyte and on the exterior of the gold layer (FIG. 55B). Surprisingly, the thicker gold layer (250 nm) produced the latter, which is desirable for discharge product removal.

[0475] EXAMPLE 11

[0476] Alkali-air batteries may be limited by poor rechargeability and low power densities, due to the formation of stable electrically insulating oxide discharge products which may passivate the air electrode surface and may not easily be decomposed. This example presents a novel sodium-humidified-oxygen fuel cell, which uses a molten sodium anode as a liquid metal fuel that can be oxidized to form a sodium hydroxide discharge product at the cathode. Under sufficiently humid conditions, this sodium hydroxide absorbs enough moisture from the input gas stream to form a liquid solution, which facilitates the removal of the discharge product from the cathode, thus preventing passivation of the cathode and allowing continuous operation of the fuel cell. Along with the use of a solid-state electrolyte, this cell chemistry can be used, in some cases, to make a “refillable primary” battery or a “metal-air fuel cell”, in which cell recharging is avoided by refilling the anode with fresh molten sodium, and the sodium hydroxide discharge products are removed and may be beneficially used, for example as a caustic, or for the capture of carbon dioxide. Said sodium hydroxide discharge products may be converted to sodium carbonate by exposure to carbon dioxide, or may be further converted to sodium bicarbonate upon exposure to water, said sodium carbonate or sodium bicarbonate being beneficially used for various purposes including as a reagent for raising the pH of water bodies.

[0477] Initial lab scale tests demonstrated a stable open circuit voltage and working voltage for upwards of 30 mAh / cm2of discharge capacity, at a current density of 2 mA / cm2and with an overpotential <0.5V. In total, the cell demonstrated 94 mAh / cm2of discharge capacity at a current density of 2 mA / cm2.

[0478] Electric power systems that can deliver high gravimetric and volumetric energy at low cost have the potential to decarbonize hard-to-abate transportation sectors such as aviation, maritime, rail transport, and long-haul trucking. Such systems could also provide stationary or transportable electric power for applications such as natural disaster relief. Technical and commercial success of metal-air electrochemical couples has been elusive, in part due to the difficulty of achieving rechargeability without using pure oxygen as a reactant, which limits the

[0479] #14431536vl discharge products to metal oxides, as opposed to more stable metal hydroxides or carbonates. The additional balance of plant necessary to provide purified oxygen can erase any system-level energy density advantage over alternatives such as lithium-ion batteries.

[0480] In this example, we show that a fuel cell based on sodium metal and air can simultaneously meet the energy density and continuous operation requirements of hard-to-abate transportation (e.g., >1 kWh / kg specific energy at cell level), at a low cost of delivered electricity comparable to that of liquid fuels, while producing a sodium oxide or hydroxide discharge product which may, in an open-system configuration, serve to capture carbon dioxide, further decarbonizing the mode of transportation. The proposed design uses liquid sodium metal (melting point 98°C) to feed a fuel cell incorporating a sodium-ion conducting solid electrolyte (here, Na- / ?” alumina), and an air cathode from which the discharge product is continuously removed. Techno-economic analysis shows the proposed fuel cell system is capable of delivering high energy density electricity at < 0.20 USD / kWh, a comparable cost to jet fuel today. The economics of electricity production may be further improved if the value of either atmospheric CO2 removal or the co-products are realized.

[0481] Metal-air electrochemical cells may have two fundamentally different designs: 1) systems in which the electrolyte is an anion conductor (e.g., alkaline electrolyte) and the discharge product (metal hydroxide or oxide) forms at the metal negative electrode, such as zinc-air, aluminum- air, and iron-air batteries; and 2) systems in which the electrolyte is a cation conductor (e.g., non-aqueous or solid-state Li and Na conductors) and the discharge product forms at the exterior of the air electrode. The second type may be the basis for a metal-air fuel cell in which the metal is continuously fed as a fluid, and the discharge product is continuously removed, in accordance with some embodiments. This example focuses on sodium metal for its combination of high crustal abundance, low cost, and high energy density, although the concepts can be applied to other metals. To facilitate discharge product removal, the input oxygen or air stream was humidified in order to form NaOH as the primary discharge product. Furthermore, this discharge product was deliquesced to concentrated sodium hydroxide liquid solutions (>50 wt% NaOH) at moderate operating temperatures (100-150°C) and water partial pressures (>~0.1 atm), allowing easy removal as a liquid and facilitating continuous discharge of the fuel cell. In this example, galvanostatic discharge was demonstrated for >150 operating hours and a cumulative area capacity > 240 mAh / cm2(about 100 times that of a typical Li-ion cell). With increasing discharge duration, the energy density of the system asymptotically approached that

[0482] #14431536vl of the fuel itself. This example demonstrates an open-loop mode of operation whereby the NaOH-water discharge product spontaneously captured ambient carbon dioxide forming sodium carbonate. Subsequent conversion to sodium bicarbonate could be utilized to de-acidify water bodies.

[0483] FIG. 51A plots the current density versus areal capacity for various lithium and sodium comparators compared to an alkali metal fuel cell in accordance with embodiments disclosed herein. FIG. 5 IB plots the power density versus energy density for various lithium and sodium comparators compared to an alkali metal fuel cell in accordance with embodiments disclosed herein.

[0484] Electrochemical Cell Design and Testing:

[0485] Two laboratory electrochemical cell designs were utilized (FIGs. 52A and 52B), an H- cell configuration with a vertically oriented solid electrolyte membrane (FIG. 52B), and a horizontally-oriented cell with a planar solid electrolyte in the form of a tray or sheet (FIG. 52A). In each design, the solid electrolyte separated the sodium metal chamber from an air cathode to which a flowing gas of controlled composition was provided. Both cell designs were configurations which with appropriate sealing and manifolding could be the basis for multi-cell stacks such as that schematized in FIG. 32C, in accordance with some embodiments. The Na- / ?” alumina used here has a sodium ion conductivity of 3.3 mS / cm at room temperature and follows an Arrhenius relationship with temperature, which was confirmed experimentally in symmetric cells with platinum blocking electrodes (FIG. 61). During discharge of the fuel cell, the anode half-cell reaction was: Na<i) = Na++ e". The liquid sodium - Na- / ?” alumina interface operates at 300-350°C. At the lower temperatures used in the present example, 100-250°C, it was confirmed experimentally that the liquid sodium-solid electrolyte interface has low impedance. A thin tin film (~50 nm thick) was sputtered on the Na- / ?” alumina to further improve its wetting by liquid sodium. The application of tin lowered the contact angle between molten sodium and Na- / ?” alumina from 125° to 50° at 125°C.

[0486] With a Na metal anode, the open-circuit voltage (OCV) was equivalent to the air cathode potential with respect to Na / Na+. At the cathode, several half-cell reactions are possible, and reaction products can form as solids or as dissolved species in an alkaline solution. The reference potentials for the solid case assume that the product formed is an anhydrous, crystalline solid, while the reference potential for the solution case assumes that the product is present in a 1 M aqueous solution:

[0487] #14431536vl 2Na++ 02+ 2 e~ = Na2O2(Esolid= 2.33 V)

[0488] Na++ 02+ e~ = NaO2Es°olid= 2.28 V, Es°oln= 2.4 V)

[0489] 4Na++ H20 + 02+ 4e- = 4NaOH (Es°olid= 2.717, Es°oln= 3.11 V ) 2Na++ H20 + 02+ 2e~ - NaOH + NaOOH Es°oln= 2.63 V)

[0490] 4Na++ 2CO2+ 02+ 4 e~ = 2Na2CO3Es°olid= 3.37 V)

[0491] In addition, if the cathode active sites are flooded or otherwise blocked from oxygen access, the anoxic Na-water reaction is also possible:

[0492] Li-air and Na-air batteries are most reversible when the discharge product is the corresponding oxide or peroxide rather than the more-stable hydroxide or carbonate. For a fuel cell where rechargeability is not required, the higher cell voltage associated with a more stable discharge product was attractive, and the selection criteria fell to which discharge product was most easily removed in order to provide for continuous operation of the fuel cell. The most stable sodium salt in air atmosphere (e.g., with ~400ppm CO2) is sodium carbonate, Na2CO3. At relative humidities and temperatures found in most places on Earth, one can also form NaOH, NaOH hydrate, or NaOH-water solutions. The hygroscopicity of sodium hydroxide means that it can deliquesce to form liquid solutions over a wide range of temperatures and humidities. The behavior of the air cathode was studied under a wide range of conditions in order to understand the half-cell reaction and identify operating conditions which minimize overpotential and maximize operational stability.

[0493] Initial experiments were conducted using a sputtered gold film of -400 nm thickness as the cathode-active layer because gold is stable at the high pH of the discharge products. Subsequent experiments were carried out using gas-diffusion layer (GDL) electrodes comprising a nickel foam. Using a cell of the configuration in FIG. 52A, discharge results at 50°C with and without humidification of an oxygen gas stream are shown in FIG. 53A. The experiments followed a galvanostatic intermittent titration test (GITT) protocol in which a constant current was applied for 15 min, followed by a 5 min rest to allow the cell voltage to relax towards the open-circuit voltage (OCV), followed by an electrochemical impedance spectroscopy (EIS) scan. Thus, the upper bound of the curves traces the OCV as the cell is discharged, while the lower bound traces the working voltage of the cell, with the horizontal axis being discharge capacity normalized to electrode area, mAh / cm2. In this example, the cells were discharged to a

[0494] #14431536vl capacity about three times that of a typical lithium-ion battery (~3 mAh / cm2). It was seen that a flowing, humidified oxygen stream produced the highest OCV and working voltage as well as the lowest polarization (voltage gap between the OCV and working voltage).

[0495] To quantify the dependence of overpotential on water activity, the temperature of the electrochemical cell was varied between 50°C and 150°C (i.e., spanning the sodium metal melting point, 98°C) and the intake water activity, a, was varied over a factor of about 200 (using a water bubbler held at 25°C to 80°C). The results in FIG. 53B show that the overpotential decreased with increasing water activity, reaching a relatively constant value above a ~ 0.1 (raw data appear in FIGs. 62A-62B). This behavior was then correlated with changes in the morphology and phase state of the discharge product. Focused ion beam (FIB) cross-sections of cells discharged at 2 mA / cm2with dry and 12% water oxygen streams are shown in FIGs. 53C and 53D, respectively (discharge data appear in FIG. 58C). For dry oxygen, the discharge product was found to form between the solid electrolyte and the gold film, disrupting the film, whereas for humidified oxygen, the discharge product formed on the exterior of the gold cathode, causing the film to remain adhered to the solid electrolyte even after thirty times higher capacity had been passed, compared to the dry oxygen case. For a cell discharged in humidified oxygen, scanning electron microscopy of the cathode surface before and after removal of the discharge product with water showed that the gold film remained largely intact and adherant to the solid electrolyte.

[0496] FIG. 53A shows GITT discharge data obtained using a sodium cell configuration in accordance with FIG. 52A, measured at 0.2 mA / cm2current density for solid sodium (50°C) under three inlet gas conditions- static oxygen at 0% RH, static oxygen at 100% RH, and continuous oxygen flow at 100% RH. The initial value of OCV was higher at 2.5 V for humidified oxygen compared to 2.4 V for dry oxygen, as was the average working voltage, 2.4 V vs 1.2 V, respectively.

[0497] FIG. 53B plots the cell overpotential, taken as the difference between cell voltage at the end of a galvanostatic segment and the OCV, shown against water activity. Increasing water activity above a ~ 0.1 led to a nearly constant overpotential.

[0498] FIG. 53C and FIG. 53D show FIB cross-section images of sodium cell stacks after discharging 0.98 mAh / cm2(9 pm thick Na metal) in dry oxygen (FIG. 53C) and 26 mAh / cm2(240 pm thick Na metal) in 12% (FIG. 53D). The sodium electrode was liquid during the test (T

[0499] #14431536vl = 105 °C). For dry oxygen the discharge product formed underneath the gold film, whereas for humidified oxygen the discharge product formed at the exterior of the gold film.

[0500] The nature of the discharge product formed under humid conditions and its reaction with ambient air was studied using X-ray diffraction. A cell discharged at 50°C to 9 mAh / cm2of sodium capacity was cooled to room temperature, purged with argon, and disassembled in an argon-filled glove box. Using an air-sensitive sample holder, the first diffraction scan was conducted under argon atmosphere, and subsequent scans were obtained upon exposing the sample to ambient air. As shown in FIG. 54A, the predominant crystalline phase was initially NaOH-FhO. While this phase was solid at the 50°C cell test temperature, according to the NaOH-FhO phase diagram, FIG. 54C, at room temperature where the X-ray experiments are conducted, a slight water excess would produce a co-existing liquid. Accordingly, within 3 minutes of air exposure, the NaOH-FhO diffraction peaks disappeared almost completely, consistent with the initial composition at NaOH-H O moving to the left into the single phase liquid field in FIG. 54C. After about 10 minutes of air exposure, diffraction peaks for Na2CO3 were observable, FIG. 54B, which then grew until saturating in intensity after about 50 min. Thus, the results showed that under humid conditions the discharge product of the sodium- air cell was initially rich in NaOH but subsequently absorbed atmospheric water, causing deliquescence, then absorbed carbon dioxide (assumed to be present at ~400ppm concentration), causing sodium carbonate to crystallize within minutes.

[0501] FIG. 54A and FIG. 54B are time-series x-ray diffraction plots. FIG. 54C plots temperature versus weight percent NaOH (%). NaOH facilitated substantial boiling point elevation, with liquid solution being stable at temperatures as high as 150 °C. The constant partial pressure curves (system pressure was 1 atm) showed that under a partial pressure of 0.12 (dew point of 50 °C), NaOH will deliquesce and remain as a single-phase liquid, up to temperatures around 120 °C. This demonstrates that it is possible to form a liquid NaOH discharge product at temperatures where Na metal is molten (> 97 °C). This can facilitate low anodic and cathodic overpotentials.

[0502] Further analysis was conducted to determine the equilibrium composition of the discharge product as a function of temperature and water activity. NaOH is capable of absorbing enough moisture from its environment to form a liquid NaOH-H2O solution, defined as deliquescence. Water absorption occurs when the ambient water vapor pressure is higher than the vapor pressure of the NaOH-H2O mixture, and can continue until the water partial pressures

[0503] #14431536vl are at equilibrium. As shown by the phase diagram in FIG. 54C, for a wide range of NaOH-FhO compositions and temperature, the corresponding composition falls in a phase field containing a liquid. However, deliquescence is not maintained indefinitely if the composition and temperature fall in the liquid-NaOH (s) two-phase regime, because the vapor pressure of the liquid phase in the two-phase equilibrium is higher than the ambient water vapor pressure. Under a flow of gas at constant humidity, the liquid phase will eventually dry out forming dehydrated NaOH. By Henry’s Law, the water vapor pressure of a solution is the product of the water activity in solution and the vapor pressure of pure water The equilibrium Na0H-H20 composition as a function of temperature and water activity was determined. Results, plotted as curves of constant water activity in FIG. 54C, show that above the melting point of sodium metal (98°C), a substantial liquid fraction can be achieved at relatively low water partial pressure, P(H2O). For example, at PfFLO) = 0.12 atm (50°C dew point), the equilibrium composition is a single-phase liquid of about 70% NaOH concentration at temperature of 105 °C. The calculated results were experimentally verified by heating solutions of known initial concentration under fixed P(H2O) until the liquidus curve was crossed and solid NaOH precipitated, and by measuring water uptake by NaOH using thermogravimetric analysis.

[0504] Fuel Cell Performance:

[0505] These results were used to design fuel cell experiments in which both the sodium and the discharge product are liquid. Operating temperatures were above the melting point of sodium such that the discharge product, even if initially solid, would deliquesce to a single-phase liquid under operating conditions, facilitating removal of discharge product as a liquid from the air cathode via wetting and gravitational flow. Results from an H-cell (FIG. 52B) with a gold film cathode and a gas diffusion electrode (GDE) are shown in FIG. 55A.

[0506] FIG. 55A plots voltage versus throughput under various conditions. FIG. 55B plots voltage versus current density at various temperatures. FIG. 55C plots DC Area Specific Resistance versus throughput under various conditions. FIG. 55D is a photo of an H-cell design.

[0507] Unlike batteries, fuel cells by design can consume fuel without limit, and therefore asymptotically approach the energy density of the fuel at long operating durations.

[0508] These observations of the discharge product provide understanding of the electrochemical reactions at the air cathode and facilitate design of the fuel cell for continuous removal of the discharge product.

[0509] #14431536vl From the GITT curves in FIG. 53A, the cell OCV was initially ~ 2.55 V for all gas compositions but equilibrated to ~ 2.4V quickly in dry oxygen and more slowly for static humidified oxygen. While in FIG. 53A the OCV remained at 2.5V for flowing humidified oxygen, this was only seen at low current density (e.g., 0.2 mA / cm2) and low total Na throughput. With continued discharge, and at higher current densities, a further decrease in OCV to 2.15-2.05 V was observed; see for example FIGs. 55A and 55B. These three characteristic OCV values were seen in the absence of CO2, so Na2CO3 formation was excluded as a possible reaction. Possible electrochemically formed products were NaO2, Na2O2, NaOH, NaOOH, and NaOH-FhO solution. Gold exhibits orientation-dependent ORR catalysis, with the (100) planes being known to be selective for 4-electron ORR forming NaOH, which has a potential of 2.64 V at 100°C, while the (110) and (111) planes are selective for the 2-electron ORR reaction forming Na2O2, which has a potential of 2.23 V at 100°C. Since the sputtered gold electrode used in these experiments was polycrystalline, it is possible that the initially observed OCV of 2.55 V was a mixed potential between those for the 2-electron and 4-electron reactions. The OCV of 2.4 V, occurring after some discharge had occurred, was likely the result of aqueous NaO2 formation, given that superoxide (O2') is the reaction intermediate for the 2-electron ORR in highly concentrated NaOH solutions. After substantial discharge and deliquescence had occurred, flooding of the cathode made Na-water reactions more likely.

[0510] Regardless of the exact electrochemical mechanism, only NaOH was observed in these ex-situ XRD measurements, since products like Na2O2, NaO2, and NaOOH would chemically react to form NaOH.

[0511] Overpotential vs. water activity

[0512] FIG. 56 plots the first discharge pulse followed by a rest at varying operating temperatures, while holding the bubbler temperature constant.

[0513] The open circuit potential and working voltage both decreased with increasing temperature, but the rate of decrease of the working voltage was higher than that of the OCV, implying an increase in overpotential with temperature. Increasing the operating temperature increased the conductivity of the electrolyte; however, it also decreased the activity of H2O due to the increase in saturation vapor pressure of H2O at higher temperatures. FIG. 53B plots the overpotential, defined as the difference between the voltage at the end of the discharge pulse and that of the resting pulse as a function of water activity. It was observed that the overpotential could be reduced either by decreasing the operating temperature or increasing the bubbler

[0514] #14431536vl temperature. The overpotential decreased with increased water activity initially, but reached a plateau at higher activity (a~ 0.1).

[0515] This example presents three lab-scale sodium-air cell designs, which are distinguished by the morphology of the anode and solid-state electrolyte. The “planar cell” used a 24-mm diameter, 1mm thick sodium beta-alumina solid electrolyte (BASE), with a 0.5 cm2sodium foil as the anode and a 50 um-thick copper foil as the anode-side current collector. The “sodium tray cell” used a BASE one-ended tube as the electrolyte filled with sodium metal, and a metal pin connected to the cell fixture at one end protruding into the sodium metal to act as the anode- side current collector. The “sodium H cell” used a glass H cell fixture with the same planar BASE electrolyte as the planar cell, and like the sodium tray cell the H cell had a steel wire currentcollector inserted into the molten sodium anode. BASE was chosen due to its commercial availability in different geometries, and all BASE components were purchased from lonotec. All cells utilized a 400-nm thick sputtered gold film as the cathode, made using a Cressington sputter coater inside of an Ar-filled glovebox. A 99.9% Au target from Ted Pella was used with a 40 mA sputtering current and a 120 sec deposition time (or a 20 mA / cm2current and a 60 sec deposition time).

[0516] For the planar cell and the tray cell, lithium-air battery fixtures purchased from MTI were used. In the case of the tray cell, the fixture was modified to include an additional O-ring to help seal the BASE tray to the fixture wall, and the metal pin to provide electrical connection to the sodium. Prior to assembly, solid electrolytes were heat-treated in an Ar glovebox at 1000 °C for 1 hr to volatilize any sodium carbonate species that formed on the pellet surface. For the planar cell, a 0.5 cm2Na foil of either 0.5 mm or 1 mm thickness was punched out and attached to the electrolyte using the copper foil current collector and an adhesive polymer ring for sealing. For the tray cell, liquid Na was dropped onto the inside of the BASE tray and allowed to solidify. For the H cell, the glass fixture was preheated and molten sodium was poured into it. The planar electrolyte with the sputtered Au film was clamped into place with a steel mesh on the air side acting as a current collector.

[0517] All cells were tested inside of a furnace (Espec / MTEYamato) in humidified oxygen. Oxygen gas flowed through an MTI mass flow controller, then through a heated bubbler to provide a certain water vapor pressure to the cells. The OCV and potentiostatic EIS scans (Biologic, 1 MHz to 100 mHz) were conducted on the cells before and after introducing humidified O2. After introducing humidified O2, the cells were ramped up to operating

[0518] #14431536vl temperature (100-105 °C). Cells were cycled using a GITT protocol (15 minutes of constant current discharge at either 1 mA / cm2or 2 mA / cm2, followed by a 5 min rest period and a potentio static EIS scan with the same parameters), until failure. SEM was performed on the cell surface after cycling, and the cathode-electrolyte-discharge product layers were characterized using XRD (Smartlab) and FIB-SEM (Helios).

[0519] Planar Cell GITT results

[0520] FIG. 57 shows GITT cycling data for two planar cells, one cycled at 1 mA / cm2(cell A) and the other at 2 mA / cm2(cell B). In both cases, the cell cycled until nearly all Na at the anode side was consumed. Cell A had a 0.5 mm-thick Na layer, which gives a total theoretical capacity of 54.2 mAh / cm2, and cell B had a 1 mm-thick Na layer, giving a theoretical capacity of 108.4 mAh / cm2. Thus, cell A used 79% of its theoretical capacity, while cell B used 88% of its theoretical capacity - the remaining capacity was lost due to leakage of water from the cathode side, which reacted with the sodium to reduce the amount available for operation. In cell A, the OCV during rest periods was roughly stable around 2.4V for the first 15 mAh / cm2, after which the OCV equilibrated to a new plateau around 2.1V. In cell B, these two OCV plateaus were also seen, though the OCV switched from 2.4V to 2.1V within the first mAh / cm2of capacity passed.

[0521] Impact of Dry vs. Humidified Gas

[0522] FIG. 53A shows a GITT discharge data at 0.2mA / cm2under three inlet gas conditions- static flow at 0% RH, static flow at 100% RH, and continuous flow at 100% RH. The initial OCV increased from 2.4V under dry conditions to 2.5V under humidified conditions. In addition, the average working voltage increased from 1.2V under static, dry O2 atmosphere to 2.4V in flowing, 100% RH O2.

[0523] SEM / FIB of discharge product in fuel cells discharged in dry vs humidified conditions

[0524] To understand the role of humidity on discharge product formation, two cells were built, one with a dry O2 gas inlet stream and one with a humidified (12% H2O) O2 inlet stream. As discussed in the previous section, the addition of humidity lowered the overpotential. FIG. 58A shows an FIB cross-section image of a cell post-mortem after passing 9um of Na for the dry conditions. FIG. 58B shows an FIB cross-section image of a cell post-mortem after passing 250um of Na for the humidified conditions. FIG. 58C plots voltage versus throughput from the dry and humidified conditions of FIGs. 58A and 58B. FIG. 58D shows schematics of the initial, dry, and humidified cells. In dry conditions, the discharge product formed underneath the gold,

[0525] #14431536vl displacing and in some areas rupturing the gold cathode layer. However, under humidified conditions, even after passing 30 times the amount of throughput, the cathode layer remained adhered to the surface. The discharge product initially formed at the triple phase boundary, where there was a discontinuity in the gold film. Under dry conditions, the discharge product continued to grow from that nucleation site, eventually rupturing the cathode and severing the electronic path. However, in humidified conditions, the discharge product could dissolve and leave the triple phase boundary site, keeping the cathode intact. Since the solubility and diffusivity of O2 in high-concentration NaOH solution is extremely low, the reaction will occur at the solid-liquid-gas interface, thus potentially facilitating reaction products to form away from the cathode-electrolyte interface. This may explain the lower overpotential observed in humidified cells.

[0526] Understanding Reaction Mechanisms

[0527] There are multiple sodium-oxygen reaction products (NaCh, Na2<D2, etc.); NaOH is also possible when moisture is present, and Na2CO3 is possible when carbon / CO2 is present. Under some of the testing conditions, CO2 was not in the gas stream and the cathode did not contain carbon, so the potential products that were formed electrochemically were NaO2, Na2O2, NaOH, and NaOOH (NaOH-H2O decomposes at 65 °C to form an NaOH-H2O solution, as seen in the phase diagram, so it was not considered). Several experimental configurations were studied in order to understand the cathode reaction mechanisms: a sputtered Au thin film electrode, an Au mesh electrode, a Pt mesh electrode, and a Pt / C microporous gas diffusion electrode. Studies with the Au thin film electrode showed that the OCV prior to cycling was around 2.55 V, which then stabilized to 2.4 V after cycling began, and eventually fell to a voltage between 2.05 - 2.15 V. An OCV of 2.4 V after some throughput had passed was likely the result of aqueous NaO2 formation - forming the O2' (superoxide) ion is the reaction intermediate for the 2-electron ORR.

[0528] Cyclic voltammetry on the Au mesh and Pt mesh electrodes showed that Pt (which is selective for the 4-electron ORR) had one oxidation and one reduction peak, suggesting a singular electrochemical reaction product, while Au (which is a non-selective catalyst capable of 2 and 4 electron ORR at different crystallographic facets) exhibited two oxidative peaks, which suggested that multiple reaction products could be generated. The reduction current in Au was much larger than its corresponding oxidation current, which suggested that the electrochemical reaction product was chemically reacting with the environment, so that there was less product

[0529] #14431536vl available for the reverse reaction (i.e., an EC-type reaction). This aligns with the possibility that the O2' ion was the electrochemical reaction product, and that aqueous NaCh quickly converted into NaOH. Since the thin film Au electrode was polycrystalline (and was thus non- selective) it is possible that the initial OCV observed before any throughput (2.55 V) was a mixed potential between the OCVs of the 2-electron and 4-electron reactions (2.23 V for the 2-electron formation of solid Na2<D2 at 100 °C, and 2.64V for the 4-electron formation of solid NaOH at 100 °C). Once the cell has passed substantial throughput, flooding of the gold surface could cause the Na- water reaction to become more likely, and thus a mixed potential between the Na-water reaction (1.88V at RT) and NaO2 formation (2.4V at RT) could be observed.

[0530] Regardless of the exact electrochemical mechanism, only NaOH was observed in the ex- situ XRD measurements, since products like Na2O2, NaO2, and NaOOH would chemically react to form NaOH. Thus, in-situ Raman spectroscopy was conducted to identify reaction products during constant current and open-circuit operation.

[0531] In-situ Raman for understanding discharge product formation mechanism

[0532] To elucidate the reaction mechanism of discharge product formation, an in-situ electrochemical Raman cell was built to identify the cathode side products during discharge. A sputtered gold film (400 nm) was used as the cathode. Before discharging, the fixture was filled with O2 flowed through a 25°C bubbler (3 % water vapor). The cell was discharged for 15 minutes at 0.25mA / cm2followed by 7 minutes at rest at an operating temperature of 25°C. A lower current density was used to prevent voiding of solid Na. Raman measurements were taken every minute during the experiment. The Raman spectrum peaks for the possible products have been reported in past Na-air literature — NaCE with a peak at 1156 cm'1, Na2<D2 with two peaks at 735 and 791 cm'1, Na2CO3 at 1078 cm'1, and NaOH at 3638 cm'1. In addition, liquid water has a broad peak between 1580 and 1640 cm'1from -OH bending modes, as well as between 3240 and 3620 cm'1from -OH stretching modes. Increasing the concentration of NaOH in aqueous solutions causes further broadening of these water peaks in addition to the increase in its characteristic peak. FIGs. 59 A and 59B show the Raman spectra measured during discharge, separated by pulse number as well as the mode (discharge versus rest), where FIG. 59B is zoomed in to 3500-3700cm-1. Initially, no peaks were detected — however, by the end of the first discharge pulse, a peak formed at 3623 cm'1, presumably NaOH, and a steady increase in the background intensity was also observed. During the second discharge pulse, there was a rapid increase in the background intensity and the NaOH peak. In the third discharge pulse, there

[0533] #14431536vl continued to be an increase in the NaOH peak, but the background intensity no longer changed. During the rest cycles, both the background intensity and the NaOH peak decreased slightly. Since no NaO2 nor Na2O2 peaks were observed over the course of the experiment, and the relative NaOH intensity remained constant during the rest, either NaOH was the primary discharge product, or any other discharge product reacted away quickly enough that its steadystate concentration was undetectable. In addition, the three cycles potentially captured the three phases of the reaction mechanism — the generation of solid NaOH, the deliquescence of NaOH (resulting in the sharp rise in the background intensity) and the continued increase in weight percentage of NaOH in the deliquesced solution.

[0534] Demonstration of discharge product removal

[0535] FIGs. 60A and 60B are planview SEM images of a cell after it had been discharged for 24mAh / cm2with a pulsed discharge of 2mA / cm2, 105 °C operation, 50°C bubbler temperature. FIG. 60A was taken after the cell had been assembled and exposed to air. The surface was covered in sheets of a low-Z phase. With EDS, these sheets were shown to have high atomic percentages of Na, C, and O (FIG. 60C) - the low Z-phase sheets were the residual discharge product left on the cathode surface. After imaging, the same cell was washed with water to remove the discharge product- the planview image after washing is shown in FIG. 60B. The sheets were no longer present due to its dissolution with water. A conformal Au cathode layer remained, highlighting the cell’s ability to reset with the addition of water.

[0536] Understanding and Modeling the Role of Humidity on Cell Performance

[0537] Ex-situ XRD measurements demonstrated that the primary discharge product observed at the cathode was NaOH. NaOH was very hygroscopic, to the point that it demonstrated deliquescence - under the right humidity conditions, NaOH is capable of absorbing enough moisture from its environment to form a liquid NaOH-H2O solution. While solid NaOH is an electronic insulator, a liquid NaOH solution can facilitate charge transfer due to the presence of dissociated ions, which prevents the formation of discharge products from rapidly increasing the ohmic resistance between the cathode and the current collector. Additionally, the formation of a liquid NaOH solution ensures that the discharge product does not block the cathode active sites from forming further discharge products, which can facilitate steady-state operation.

[0538] Deliquescence occurs when the water vapor pressure over the NaOH is lower than the ambient water vapor pressure, thus providing a driving force for the uptake of water from the environment. Equilibrium is achieved when the vapor pressure of the NaOH solution (L) equals

[0539] #14431536vl the ambient vapor pressure. By Henry’s Law, the water vapor pressure of a solution is the product of the water activity in solution, and the vapor pressure of pure water. Thus,

[0540] P „H am2Obient > — P „HL2O > —nUHL2OPH °2O

[0541] Given a model for the activities in an NaOH-H2O solution, it should be possible to predict the equilibrium water content for an NaOH solution as a function of ambient vapor pressure and temperature. Combining these predictions with the NaOH-H2O phase diagram will show which temperatures and ambient vapor pressures will yield an NaOH-H2O composition that is in the single-phase liquid regime of the phase diagram.

[0542] The temperature versus composition curves for NaOH under varying pH2Os were calculated. These curves show that under constant pH2O, increasing temperature will result in higher concentration NaOH solutions, until the curves cross the liquid phase boundary, and solid NaOH begins to precipitate out of solution. This predicted behavior was validated by observing the appearance of NaOH at constant pH2O with varying temperatures, and by measuring water uptake by NaOH through thermogravimetric analysis.

[0543] Conclusion

[0544] In this example, we demonstrated a sodium-air fuel cell concept that achieved the highest areal capacity and power density ever demonstrated. High current density operation with low overpotential and large metal anode loadings were achieved by the deliquescence of the NaOH discharge product, which facilitated the formation of a liquid NaOH solution at temperatures well above the melting point of Na metal, thus eliminating voiding issues on the anode side, and electrode clogging / passivation on the cathode side. The abundance of Na metal means that it is feasible to operate this cell in a discharge-only mode and either dispose of or collect the discharge that is produced.

[0545] Concept schematic in multi-stack configuration

[0546] FIG. 32C shows a conceptual drawing of a multi-stack module based on single stack in series and parallel, in accordance with some embodiments.

[0547] Ionic conductivity of Na- fl” alumina

[0548] Symmetric cells were built to measure the ionic conductivity of Na- / ?” alumina. Roughly 400 nm of platinum was deposited on both sides of the solid-state-electrolyte, and was sandwiched between two pieces of copper foil, and pressed between two stainless steel plates loaded with springs. Electrochemical impedance spectroscopy was used to measure the bulk

[0549] #14431536vl resistance of Na- / ?” alumina. All measurements were conducted in the glovebox at <0.1 ppm O2 level and <0.1 ppm H2O level.

[0550] FIG. 61 shows the temperature dependence of the ionic conductivity of Na- / ?” alumina measured with electrochemical impedance spectroscopy. The conductivity follows an Arrhenius relationship, where the log of GT scales linearly with the inverse of temperature. Overpotential vs. water activity

[0551] FIGs. 62A-62B plot the first discharge pulse followed by a rest at varying cell and bubbler temperatures, which was used to calculate the overpotential as a function of water activity in FIG. 53B. In FIG. 62A, the cell temperature was varied while the bubbler temperature was held constant, and in FIG. 62B, the bubbler temperature was varied while the cell temperature was held constant. The overpotential was calculated as the difference between the voltage at the end of the discharge pulse and that of the resting pulse. The activity at each condition was calculated as follows:

[0552] The overpotential decreased with water activity, which can be lowered either by decreasing the cell temperature or increasing the bubbler temperature (see Table 2).

[0553] FIGs. 62A and 62B show a first discharge pulse followed by rest at varying cell and bubbler temperatures (15 minutes at ImA / cm2followed by a 5 minute rest with a 50nm sputtered gold film cathode). FIG. 62A uses a fixed bubbler temperature of 25 °C. FIG. 62B uses a fixed cell temperature of 100 °C.

[0554] Table 2: Activity of water at different cell and bubbler temperatures

[0555] FIB cross-section comparison of dry vs. humidified inlet gas stream

[0556] #14431536vl FIG. 58B shows a GITT comparison between dry and humidified inlet gas stream (15 minutes at 2 mA / cm2, followed by a 5 minute rest) using a 400 nm sputtered gold film cathode. The working voltage was lower when using a dry inlet stream compared to a humidified inlet stream.

[0557] FIGs. 63A and 63B show EDS mapping of FIB cross-sections following discharge in dry (FIG. 63 A) and humidified conditions (FIG. 63B).

[0558] Deliquescence

[0559] Two sets of experiments were conducted to study deliquescence. First, some anhydrous NaOH powder (stored in an Ar-filled glovebox) was transferred into a gas washing bottle which was connected to a source of humidified Ar (Ar bubbled through room temperature water). The NaOH powder was placed on a hot plate, and the hot plate temperature was varied. It was observed whether the NaOH powder had transformed into a liquid solution, and vice versa. Using Ar instead of atmospheric air prevents the NaOH from being converted into Na2CO3. The experimental setup is shown in FIG. 64.

[0560] The results from this study are shown in FIG. 65.

[0561] These images suggest that the onset of deliquescence (when the equilibrium NaOH concentration crosses into the liquid phase of the phase diagram), occurs around 90°C under 0.03 atm of water vapor (the saturation vapor pressure at 25C). However, due to the qualitative nature of this study, and since there was the risk of forming Na2CO3 over the long timescales needed to observe deliquescence and recrystallization, the deliquescence was further validated using TGA.

[0562] The TGA experiment involved placing some NaOH powder in a platinum pan and quickly ramping up the temperature to 150°C and holding under flowing humidified Ar. Even though the Ar was humidified, at 150°C the equilibrium NaOH concentration was far from the single-phase regime, and thus the NaOH dehydrated. After the weight started stabilizing, the temperature was brought down to 100°C, and the weight continued stabilizing, since 100°C is also too high of a temperature for NaOH to absorb moisture (under those humidity conditions). Once the weight had finally stabilized, the temperature was decreased and held at various lower temperatures, and the stabilized weights were used to determine the water content, assuming that the weight after the 100°C isothermal hold gives the mass of the NaOH in the system. The mass vs time data is shown in FIG. 66.

[0563] #14431536vl Using the data in FIG. 66, the NaOH weight percentage was calculated at 80°C, 85°C, 90°C, and 95°C, as shown in Table 3.

[0564] Table 3: Temperature versus NaOH wt% from thermogravimetric analysis (TGA)

[0565] This experimental data demonstrates NaOH deliquescence behavior.

[0566] EXAMPLE 12

[0567] A continuously operating sodium-oxygen fuel cell was developed that achieved an energy density of 1000 Wh / kg, a power density of 170 W / kg, and a capacity of 400 mAh / cm2, at a form factor of 0.5 cm2with an operating current of 100 mA / cm2and an operating voltage of 1.93V. The fuel cell had an H-cell configuration (see FIG. 52B). The anode comprised an anodic reactant comprising liquid sodium metal. The cathode was a gas diffusion cathode comprising a porous PTFE film, a Ni foam substrate, and a microporous layer adorned with catalyst. Linear sweep voltammetry results suggested that this design is capable of achieving a current density of 330 mW / cm2, which would result in a power of 0.35 W / cm2.

[0568] Visual confirmation showed formation of a liquid discharge product under oxygen at 120 °C with a partial water pressure of 0.46 atm. The liquid discharge product flowed down the cell and settled in the cathode chamber.

[0569] EXAMPLE 13

[0570] A continuously operating sodium-air fuel cell was developed that discharged at 80 mA / cm2with an average voltage of 1.32V for 2360 mAh / cm2(1188 Wh / kg, 40 W / kg, capacity equivalent to 2.1 cm thickness of Na). The fuel cell had a liquid tray fixture configuration (see FIG. 52A) and was operated at 110 °C using an air flow with a partial water pressure of 0.46 atm. The fuel cell achieved an energy density of 1188 Wh / kg, a capacity of 2360 mAh / cm2, and a power density of 40 W / kg, at a form factor of 0.12 cm2.

[0571] #14431536vl EXAMPLE 14

[0572] A Na-air fuel cell, in which the discharge product forms in between the solid electrolyte and air cathode, was developed. The discharge product was removed from the fuel cell via inplane flow to the edge of the air electrode. The fuel cell operated at 120 °C, using a liquid Na anode, a sodium-beta-alumina solid-state electrolyte tray, and an gas diffusion cathode. The tray was oriented so that the Na anode was depleted in the direction of gravity. The voltage, current, and power for this fuel cell are shown in FIG. 74.

[0573] EXAMPLE 15

[0574] This example describes electrolytic production of Na metal from aqueous NaOH solution.

[0575] In this example, an electrolytic NaOH- splitting reactor is demonstrated, which decomposes concentrated NaOH aqueous solutions to Na metal at a negative electrode, and water and oxygen at a positive electrode, at moderate temperatures below 200°C. An electrolyzer of such design may be used to convert the sodium oxide or sodium hydroxide product of an energy generating reaction, including but not limited to thermal oxidation of sodium metal, reaction of sodium metal with water, or electrochemical oxidation of sodium metal as in a sodium- air fuel cell or battery.

[0576] In the instance where the reaction product of such energy-generating reaction is a sodium oxide, a sodium hydroxide or a sodium hydroxide-water mixture may be obtained from said sodium oxide in the reacted mixture upon reaction with water. In accordance with certain embodiments, the negative and positive electrodes are separated by a solid sodium ion conductor, thereby preventing contact or crossover of water or oxygen with the sodium metal. H-cell reactors as illustrated in FIG. 78 were fabricated. 1 / 16” silicone gaskets with adhesive backing (source: 3M) of 14 mm inner diameter and 28 mm outer diameter were laser cut and applied to the H-cell chambers (source: Adams & Chittenden). A nickel wire was spot welded to a platinum gauze (5 x 5 mm, source: Thermo Scientific) to form a working electrode (positive electrode). A layer of tin was sputtered onto a sodium ^’’-alumina (NBA) disc (1 mm thick, source: lonotec) to improve sodium wetting. An H-cell chamber, sodium ^’’-alumina disc, and another H-cell chamber were clamped together to form the assembly illustrated in FIG. 78. The platinum electrode was inserted into one H-cell chamber, which was filled with 3 mL sodium hydroxide solution prepared from anhydrous sodium hydroxide and deionized water in a 50:50 or 30:70 weight ratio. The other chamber was filled with sodium metal, to which was contacted

[0577] #14431536vl a nickel wire, forming the counter electrode (negative electrode). The temperature of the cell was raised to either 110 °C or 130 °C, at which temperatures both the sodium metal and the NaOH- water solutions are liquids. An electrochemical formation cycle was conducted, consisting of the passage of a current density of 1 mA / cm2(where the area is taken to be the planar area of the platinum gauze) for 5 minutes, followed by 5 minutes of rest during which an EIS scan was taken. In this experiment, the platinum mesh is the anode and the sodium metal is the cathode, driving an overall reaction 4 NaOH — 4 Na + 2 H2O + O2. Following the formation cycle, linear sweep voltammetry was conducted, starting from the open circuit voltage of the cell and increasing the voltage at a rate of 10 mV / s until the current density, which was simultaneously measured, reached 1 A / cm2(FIG. 79). Subsequently, a stepped galvanostatic test was conducted in which the cell was subjected to 30 minutes of constant current and 5 minutes of rest, followed by an EIS scan. In the stepped galvanostatic test, the initial current density was 25 mA / cm2, and in each subsequent step the current density was increased by 25 mA / cm2, until a current density of 500 mA / cm2was reached (FIG. 80). A cumulative mass of 2.253 g of sodium metal was produced during this experiment.

[0578] FIG. 81 shows results from said NaOH- splitting electrolyzer, plotted as current density (left vertical axis) and sodium metal production rate per unit area (right vertical axis) against cell voltage (horizontal axis). Also shown as horizontal axes at the top of the figure are scales for the energy consumed per kilogram of sodium metal produced, and the electricity cost per kilogram of sodium metal produced, the latter assuming an electricity rate of $0.05 / kWh. Curves are shown for both the linear sweep voltammetry (LSV) measurements and the stepped galvanostatic measurements, for which the final voltage of each charge is shown. Results for a 30:70 NaOH:water solution operating at a cell temperature of 110°C and for a 50:50 NaOH:water solution operating at 130°C are shown. Also shown are estimated resistance contributions for charge-transfer resistance alone and for the solid state electrolyte (SSE) resistance alone. Results are compared to a typical Downs cell, representing the industry state- of-art, for producing Na from NaCl at a temperature of about 580°C. The results show that sodium production is achieved at lower voltage, lower temperatures, and comparable current densities to the Downs cell.

[0579] It is understood from this example that a wide range of NaOH-water ratios and temperatures may be used in said electrolyzer. FIG. 82 shows the water-NaOH phase diagram, with temperature as the vertical axis and NaOH concentration as the horizontal axis. In some

[0580] #14431536vl embodiments, the solution composition and temperature may be selected to be anywhere within the single-phase liquid field labeled “UNSATURATED SOLUTION”, or any field of the phase diagram where an NaOH bearing liquid labeled “SOLN” may be present. Accordingly, the temperature of the NaOH solution or of the electrolyzer may range from as low as -25 °C to as high as 325°C. In can be preferred in some embodiments, that said electrolyzer is operated at a temperature where said sodium-ion conducting solid electrolyte has an appreciable sodium ionic conductivity, preferably above about 1 mS / cm, in order to have a high current density and rate of sodium metal production at a low voltage, preferably in some embodiments below about 8 V. It can be preferable in some embodiments if said electrolyzer is operated at a temperature above the melting point of the sodium, in order to facilitate easier collection of said sodium, and below the boiling point of the NaOH-water solution, which for a pressure of 1 atm is indicated by the curve in EIG. 82 labeled “P = 1 atm”. In can be preferable in some embodiments if said NaOH- water solution used in said electrolyzer has a high NaOH concentration in order to decrease the volume of solution that is used, and to increase the conductivity of the solution. Accordingly, in some cases, it can be preferred for the operating temperature and NaOH concentration to be in a field in EIG. 82 shown as the shaded region, falling above about 98C and below the curve labeled “P = 1 atm”. As pressure, P, increases, said curve will move up and to the left, enlarging said field of operation that is preferred in some embodiments. Also, from PIG. 81, all else being equal, a higher sodium ionic conductivity will move the curve labeled “SSE ohmic” to the left, lowering the SSE ohmic resistance and allowing a higher current density at a lower voltage. Also, all else being equal, for a given anode, a higher surface area may lower the charge transfer resistance, moving the curve labeled “charge transfer” to the left and allowing a higher current density at a lower voltage.

[0581] EXAMPLE 16

[0582] Driven by a combination of population growth and rising standards of living, the demand for energy is increasing faster than the capacity of energy transmission networks. Energy generation, particularly from renewable resources such as wind and solar, can be separated from demand both geographically (in the United States, wind and solar generation are concentrated in the Midwest and Southwest, while energy demand is highest along the coasts), and temporally (due to the intermittent nature of wind and solar). As a result, efficient and economic modes of energy transmission are required.

[0583] #14431536vl Currently, a vast majority of electrical energy is transmitted via high-voltage transmission lines, which comprise bundles of conducting wire supported by pylons. The United States’ transmission system includes 180,000 miles of high-voltage transmission line. While the need for transmission infrastructure expansion is well documented, the construction of additional transmission line remains plagued by several challenges. Planning, cost allocation, and siting and permitting are all complicated by the multi-regional nature of transmission lines. Transmission projects can benefit a variety of stakeholders, and evaluating the expected benefit across multiple jurisdictions in order to allocate costs can be challenging. Furthermore, securing a right-of-way across multiple jurisdictions requires unanimous approval, and can face opposition on the grounds of harmful impact on the local environment. Finally, transmission infrastructure is typically geared towards connecting a few large central generators to the grid rather than many small solar or wind projects, which can pose different challenges.

[0584] Chemical energy carriers play a large role in today’s energy ecosystem. Natural gas, composed primarily of methane, is shipped via pipeline to roughly 2,000 power plants across the United States, where its combustion accounts for 38% of the country’s primary energy production. However, natural gas is a limited resource, and both extraction and consumption can cause environmental damage. Hydrogen has been proposed as a circular energy carrier, with a “hydrogen economy” comprising electrolyzers to utilize energy from renewable resources to produce hydrogen gas, fuel cells to recover energy from hydrogen, and a hydrogen transportation infrastructure to connect the two. Technical challenges in all three sectors of the hydrogen economy, most notably in the development of a hydrogen transportation infrastructure, have prevented its widespread adoption.

[0585] The sodium-air fuel cell described herein has the potential to provide for sodium metal as an energy carrier to address the growing need for energy transmission, in some embodiments. In some embodiments, an electrolytic process by which sodium metal fuel is restored from the fuel cell discharge product, aqueous sodium hydroxide, “closes the loop.” Such a process would provide for a sodium-based energy ecosystem, depicted in FIG. 83, in which sodium metal is shipped to areas with high energy demand and high cost of energy, where it is consumed by the fuel cell to produce energy and sodium hydroxide discharge product, in accordance with some embodiments. The discharge product is shipped to areas with low cost of energy, such as areas with a high capacity of renewable but intermittent energy sources, where sodium metal is electrolytically restored, completing the cycle, in accordance with certain embodiments.

[0586] #14431536vl Sodium metal was once produced at high volumes as a commodity chemical for use in the production of the now-prohibited gasoline additive tetraethyllead. At its peak in the 1970s, the annual sodium metal production and transportation capacity within the United States exceeded 200,000 tons, with the DuPont company responsible for a lion’s share. With this amount of sodium, the fuel cell described herein could produce over 400 GWh of energy, in certain embodiments. Since the banning of tetraethyllead, sodium has continued to be used in chemical manufacturing and as a coolant in nuclear reactors, though it is now produced in smaller quantities.

[0587] Presented in this example is an electrolysis cell for the reduction of sodium from aqueous sodium hydroxide. This device incorporated a solid-state electrolyte to separate the sodium hydroxide from the produced sodium, allowing for the use of an aqueous rather than molten sodium hydroxide feedstock and preventing the products from reacting with one another, resulting in lower operating temperatures and higher faradaic efficiencies. The electrolysis of aqueous sodium sulfide was also explored.

[0588] Methods

[0589] Results and Discussion

[0590] Experimental Setup

[0591] In each experiment, an H-cell was prepared to carry out the reduction of sodium metal from a sodium containing solution. FIGs. 84A-84B and 84A-84B show various H-cell configurations. Within a glovebox with an inert argon atmosphere, a 19 mm diameter, 100 nm tin layer was sputtered (Cressington 108 A sputter coater, 20 mA, 120 s) onto a 24 mm diameter, 1 mm thick sodium / T-alumina pellet (lonotec), which was placed between silicone gaskets to form an assembly which was clamped between the H-cell chambers, with the sputtered tin side of the pellet facing the cathode chamber. The cathode chamber was filled with either sodium or mineral oil. When filling the cathode chamber with sodium, both the sodium and the H-cell were brought to 150 °C to allow for the pipetting of liquid sodium without clogs caused by freezing. In this case, a nickel wire was inserted through a septum in the cathode chamber cap and submerged within the sodium to serve as an electrical contact (see FIGs. 84A-84B). The tin improved the contact between the liquid sodium and the pellet face. Alternatively, when filling the cathode chamber with mineral oil, an 80 mesh, 0.14 mm wire, stainless steel mesh (Alfa Aesar) current collector was placed between the sputtered tin layer on the sodium / T-alumina

[0592] #14431536vl pellet and the adjacent silicone gasket, protruding beyond the gasket to serve as an electrical contact (see FIGs. 86A-86B). In this case, initial charging sodiated the tin. As more charge was passed, liquid sodium replaced the tin layer, and eventually passed through the steel mesh and into the cathode chamber. All caps were affixed before removing the cell from the glovebox to prepare the anode chamber.

[0593] In order to minimize exposure time, the anode chamber caps were removed just prior to anode chamber preparation, which was carried out as quickly as possible. A 0.02 in diameter nickel wire (Fischer Scientific, 99.5%) was spot welded (60 Ws Unitek fine wire spot welder, 6% power) to a 5 mm x 5 mm anode of varying composition and was inserted through a septum in the anode chamber cap, allowing for electrical contact while suspending the anode within the chamber. The sodium containing solution was added to the anode chamber, and the caps were once again affixed. A needle was inserted through the anode chamber cap to avoid pressurizing the chamber via electrolytically produced gaseous species. The H-cell was placed in an oven (Yamato) and given an hour for temperature equilibration before electrical testing (Biologic VMP3).

[0594] Electrolysis of Aqueous Sodium Hydroxide

[0595] The first iteration of the cell implemented a sodium metal current collector in the cathode chamber, a 52 mesh, 0.1 mm wire, platinum mesh (Thermo Scientific, 99.9%) as the anode, and sodium hydroxide solution as the sodium feedstock in the anode chamber as depicted in FIGs. 84A-84B. Sodium hydroxide solution (50 wt %) was prepared by weighing and mixing 4.5 g of sodium hydroxide pellets (Sigma Aldrich, >98%) and 4.5 g of DI water in ambient atmosphere.

[0596] Upon charge, sodium ions were reduced at the cathode, while hydroxide ions were oxidized at the anode.

[0597] Cathode: Na++ e- — > Na^)

[0598] Anode :

[0599] This yielded an estimated OCV of 2.797 V.

[0600] A formation charge current of 0.1 mA / cm2was applied until the OCV underwent a marked increase while the cell resistance underwent a marked decrease, attributed to the sodiation of the sputtered tin layer. After formation, the cell was tested using linear sweep voltammetry (LSV) with a 10 mV / s scan rate, then a GITT current ladder with 15 minute pulses and 5 minute rests. The tests were applied to cells at 110 °C and 130 °C.

[0601] #14431536vl - I l l -

[0602] Electrical test results for the first iteration of the cell are shown in FIGs. 85A-85C. The GITT showed an OCV of around 2.7 V, consistent with equation 1, and the LSV was able to achieve 0.65 A / cm2at 7 V and 1.75 A / cm2at 5.44 V at 110 °C and 130 °C respectively. While both the LSV and GITT probe the current-voltage performance of the system, the LSV is more forgiving by virtue of its shorter timescale. The geometry of the cell included a 1 cm diffusion path through sodium hydroxide solution. At high current densities, liquid electrolytes are subject to concentration gradients which can decrease the overall conductivity, leading to a maximal possible current known as the “limiting current.” This effect is more apparent in the GITT pulses, which happen on the order of 15 - 30 minutes, than the LSV, which happens on the order of 5 minutes. Both the GITT and LSV highlight temperature as a means to enhance kinetics and decrease the overpotential.

[0603] At higher current densities, bubbles were observed at the platinum mesh anode, also consistent with equation 1, as well as along the submerged portion of the nickel wire contact. The next iteration of the sodium reduction H-cell used a nickel foam (Fuel Cell Store, 80 - 120 PPI) as an anode, and mineral oil in the cathode chamber. The mineral oil protected the produced sodium. A stainless steel mesh current collector was placed between the pellet and the cathode side silicone gasket as depicted in FIGs. 86A-86B to serve the role of current collector. The cell was tested at 120 °C with a formation charge, LSV, then a single current density GITT with 15 minute pulses at 40 mA / cm2and 5 minute rests, shown in FIGs. 87A-87B.

[0604] The cell performance was in line with the previous design, with the GITT showing an OCV of 2.709 and the LSV achieving 1.41 A / cm2at 5 V. The cell was able to pass 668 mAh of charge during the GITT test, corresponding to the production of 0.573 g of sodium metal, which can be observed in FIG. 86B.

[0605] Electrolysis of Aqueous Sodium Sulfide

[0606] In order to reduce sodium from an aqueous solution of sodium sulfide, the cell design shown in FIGs. 86A-86B was used. Sodium sulfide solution was prepared weighing and mixing 2.602 g of sodium sulfide powder (Sigma Aldrich) and 2.60 g of DI water at 120 °C in ambient atmosphere. The 50 wt % composition was selected to elevate the boiling point of the solution above the operating temperature of 120 °C, which in turn was chosen both to give good comparison to previous cells, and to exceed the melting point of pure sulfur, 113 °C. Though sulfur is more soluble in alkaline solutions, production of liquid rather than solid sulfur may help

[0607] #14431536vl to avoid anode clogging, in some embodiments. Upon dissociation in water, sodium sulfide underwent further reaction to produce hydrosulfide and hydroxide ions:

[0608] Upon charge, sodium ions were reduced at the cathode, while hydrosulfide, hydroxide, and / or sulfide ions were oxidized at the anode.

[0609] Cathode: Na++ e- — > Na^)

[0610] Anode:

[0611] 1Q1

[0612] Anode: - S2— > - S + e

[0613] 2 2

[0614] This yielded an estimated OCV of 1.992 V.

[0615] The 50 wt % sodium sulfide solution had a freezing point of around 100 °C, which led to it freezing as it was poured into the anode chamber. The H-cell chamber should be preheated to avoid freezing, in some cases.

[0616] The cell was tested with the same formation, LSV, and GITT recipe sequence, shown in FIGs. 88A-88B, though the GITT consisted of 15 minute pulses at 160 mA / cm2and 5 minute rests. During the GITT, an OCV of 1.721 V was observed. The LSV was able to achieve a current density of 1.2 A / cm2at 6 V.

[0617] The sodium sulfide solution cell showed a lower OCV than the sodium hydroxide solution cell (1.721 V vs 2.709 V). No bubbles were observed at the anode, even at high current densities, consistent w...

Claims

CLAIMSWhat is claimed is:

1. A method, comprising: initiating contact between a reducing reagent and a metal-bearing compound such that metal within the metal-bearing compound is reduced to one or more metals while a salt of said reagent is produced; and subsequently regenerating the reducing reagent from the salt.

2. The method of claim 1, wherein regenerating the reducing reagent comprises performing thermal, electrochemical, thermochemical, photochemical, and / or mechanochemical decomposition of the salt.

3. The method of claim 1, wherein regenerating the reducing reagent comprises performing electrochemical decomposition of the salt.

4. The method of any one of claims 1-3, wherein the metal-bearing compound comprises a metal salt.

5. The method of claim 4, wherein the metal-bearing compound comprises a metal oxide, a metal chalcogenide, a metal sulfide, a metal halide, a metal chloride, a metal hydroxide, a metal carbonate, a metal sulfate, a metal carbide, and / or a metal nitride.

6. The method of any one of claims 1-5, wherein the reducing reagent comprises a metallic metal.

7. The method of claim 6, wherein the metallic metal is an alkali metal.

8. The method of claim 7, wherein the alkali metal is lithium, sodium, or potassium.

9. The method of claim 7, wherein the alkali metal is sodium.#14431536vl10. The method of any one of claims 1-9, wherein the metal-bearing compound comprises copper sulfide.

11. The method of any one of claims 1-10, wherein the metal-bearing compound comprises copper iron sulfide (e.g., chalcopyrite).

12. The method of any one of claims 1-11, wherein the reducing agent is sodium.

13. The method of any one of claims 1-12, further comprising discharging an alkali metal fuel cell to provide energy in the form of electric power and / or heat prior to the initiating contact step and / or the regenerating step, wherein the provided energy is used in the initiating contact step and / or the regenerating step.

14. The method of any one of claims 1-13, further comprising combusting a fuel comprising sodium to provide energy prior to the initiating contact step and / or the regenerating step, wherein the provided energy is used in the initiating contact step and / or the regenerating step.

15. The method of claim 3, wherein the electrochemical decomposition of the salt is performed in an electrochemical cell, wherein: the electrochemical cell is configured to produce the reducing reagent, and (1) the electrochemical cell is configured such that the salt is supplied to the electrochemical cell from a source external to the electrochemical cell and / or (2) the electrochemical cell is configured such that the produced reducing reagent can be removed from the electrochemical cell.

16. The method of claim 15, wherein the produced reducing reagent is the reducing reagent of any one of claims 6-9.#14431536vl17. The method of any one of claims 15-16, wherein the electrochemical cell comprises a first electrode comprising the reducing reagent and a second electrode comprising the salt, wherein the first electrode and the second electrode are separated by a solid electrolyte.

18. The method of claim 17, wherein the first electrode comprises metallic sodium, the second electrode comprises a sodium salt, and the solid electrolyte comprises a sodium ion-conducting solid electrolyte.

19. The method of claim 18, wherein the sodium salt comprises sodium sulfide and / or sodium poly sulfide.

20. The method of any one of claims 1-19, wherein the one or more metals comprises copper, iron, nickel, lead, zinc, silver, molybdenum, tungsten, mercury, arsenic, cobalt, and / or antimony.

21. The method of any one of claims 1-20, wherein the one or more metals comprises copper and / or iron.

22. The method of any one of claims 1-21, wherein the one or more metals comprises a mixture and / or an alloy comprising two or more of copper, iron, nickel, lead, zinc, silver, molybdenum, tungsten, mercury, arsenic, cobalt, and / or antimony.

23. The method of any one of claims 1-22, wherein the metal-bearing compound comprises ferrous sulfide (FeS), pyrite (FeS2), nickel sulfide (NiS), lead sulfide (PbS), zinc sulfide (ZnS), silver sulfide (Ag2S), molybdenum sulfide (M0S2), tungsten sulfide (W2S), mercury sulfide (HgS), antimony sulfide (Sb2S3), and / or arsenic sulfide (AsS).

24. The method of any one of claims 1-23, wherein the metal-bearing compound comprises a mixed-metal sulfide.#14431536vl25. The method of claim 24, wherein the mixed- metal sulfide comprises chalcopyrite (CuFeS2), bornite (CusFeS4), pentlandite (Fe,Ni)9Ss), cobaltite ((Co,Fe)AsS), tetrahedrite (Cui2Sb4S 13) and / or tennantite (CU12AS4S13).

26. The method of any one of claims 1-25, further comprising purifying the produced metal.

27. The method of claim 26, wherein purifying the produced metal comprises electrolytic purification of the produced metal.

28. A system configured to perform the method of any preceding claim.

29. The system of claim 28, wherein the system comprises a subsystem for contacting a reducing reagent and a metal-bearing compound and an electrochemical cell.

30. The system of claim 29, further comprising a subsystem for purifying a produced metal.

31. A system comprising: an alkali metal fuel cell; and an electrochemical cell; wherein the alkali metal fuel cell comprises: a cathode comprising a cathodic reactant comprising gaseous oxygen, gaseous water, and / or gaseous carbon dioxide; and an anode comprising an anodic reactant comprising an alkali metal; and wherein the electrochemical cell comprises: a first electrode comprising electrode active material comprising metallic alkali metal; a second electrode comprising an alkali metal-containing material; and#14431536vla solid electrolyte that conducts alkali metal ions in electrochemical communication with the first electrode and the second electrode; wherein the electrochemical cell is configured to produce a metallic metal, wherein: the electrochemical cell is configured such that the alkali metalcontaining material is supplied from a source external to the electrochemical cell and / or the electrochemical cell is configured such that the produced metallic metal can be removed from the electrochemical cell.

32. The system of claim 31, wherein the alkali metal of the anodic reactant is liquid alkali metal.

33. The system of any one of claims 31-32, wherein the produced metallic metal comprises a produced metallic alkali metal.

34. The system of claim 33, wherein the system is configured such that the produced metallic alkali metal replenishes the alkali metal of the anodic reactant.

35. The system of any one of claims 31-34, wherein: the cathodic reactant comprises gaseous water; the alkali metal fuel cell is configured to produce a discharge product; and the discharge product comprises an alkali metal hydroxide, and at least a portion of the alkali metal hydroxide is in the form of a liquid solution.

36. The system of claim 35, wherein the system is configured such that the alkali metal hydroxide discharge product replenishes the alkali metal-containing material of the second electrode.

37. The system of any one of claims 31-36, wherein:#14431536vlthe alkali metal fuel cell comprises a solid electrolyte; and the solid electrolyte of the alkali metal fuel cell is below the anode and the cathode is below the solid electrolyte of the alkali metal fuel cell in the direction of gravitational pull.

38. The system of any one of claims 31-37, wherein: the anodic reactant comprises a layer of the liquid alkali metal; and the layer of liquid alkali metal has a thickness of greater than or equal to 1 millimeter and less than or equal to 5 centimeters.

39. The system of any one of claims 31-38, wherein: the anodic reactant comprises a layer of the liquid alkali metal; and the alkali metal fuel cell is configured such that the liquid alkali metal is not replenished during its period of operation.

40. A method, comprising discharging the alkali metal fuel cell of any one of claims 31-39 to produce an electric current.

41. The method of claim 40, further comprising replenishing the alkali metal of the anodic reactant with the produced metallic alkali metal.

42. The method of any one of claims 40-41, further comprising replenishing the alkali metal-containing material of the second electrode with the alkali metal hydroxide discharge product.

43. The system or method of any one of claims 31-42, wherein the produced metallic metal comprises produced metallic sodium.

44. The system or method of any one of claims 31-43, wherein the produced metallic metal comprises produced metallic lithium.#14431536vl45. The system or method of any one of claims 31-44, wherein the produced metallic metal comprises produced metallic potassium.

46. The system or method of any one of claims 31-45, wherein the metallic alkali metal of the electrode active material is liquid metallic alkali metal.

47. The system or method of any one of claims 31-46, wherein the metallic alkali metal of the electrode active material comprises metallic lithium.

48. The system or method of any one of claims 31-47, wherein the metallic alkali metal of the electrode active material comprises metallic sodium.

49. The system or method of any one of claims 31-48, wherein the metallic alkali metal of the electrode active material comprises metallic potassium.

50. The system or method of any one of claims 31-49, wherein the alkali metalcontaining material is anhydrous or aqueous.

51. The system or method of any one of claims 31-50, wherein the alkali metalcontaining material comprises an alkali metal hydroxide.

52. The system or method of any one of claims 31-51, wherein the alkali metalcontaining material comprises lithium hydroxide.

53. The system or method of claim 52, wherein the lithium hydroxide of the alkali metal-containing material is in the form of an aqueous lithium hydroxide solution.

54. The system or method of any one of claims 31-53, wherein the alkali metalcontaining material comprises potassium hydroxide.#14431536vl55. The system or method of claim 54, wherein the potassium hydroxide of the alkali metal-containing material is in the form of an aqueous potassium hydroxide solution.

56. The system or method of any one of claims 31-55, wherein the alkali metalcontaining material comprises sodium hydroxide.

57. The system or method of claim 56, wherein the sodium hydroxide of the alkali metal-containing material is in the form of an aqueous sodium hydroxide solution.

58. The system or method of any one of claims 31-57, wherein the alkali metalcontaining material comprises an alkali metal sulfide.

59. The system or method of claim 58, wherein the alkali metal sulfide comprises sodium sulfide.

60. The system or method of claim 59, wherein the sodium sulfide is in the form of an aqueous sodium sulfide solution.

61. The system or method of any one of claims 31-60, wherein the electrochemical cell comprises a liquid that is inert with respect to the produced metallic metal.

62. The system or method of claim 61, wherein the electrochemical cell is configured to transport the produced metallic metal directly into the liquid that is inert with respect to the produced metallic metal.

63. The system or method of any one of claims 61-62, wherein the liquid that is inert with respect to the produced metallic metal comprises an oil.

64. The system or method of any one of claims 61-63, wherein the liquid that is inert with respect to the produced metallic metal has a density higher than that of the produced#14431536vlmetallic metal in solid state below its melting point and / or in liquid state above its melting point.

65. The system or method of any one of claims 61-64, wherein the liquid that is inert with respect to the produced metallic metal has a density lower than that of the produced metallic metal in solid state below its melting point and / or in liquid state above its melting point.

66. The system or method of any one of claims 61-65, wherein the liquid that is inert with respect to the produced metallic metal has a density intermediate between that of the produced metallic metal in solid state below its melting point and that of the produced metallic metal in liquid state above its melting point.

67. The system or method of any one of claims 31-66, wherein the solid electrolyte of the electrochemical cell is in the form of a container that contains the metallic alkali metal of the electrode active material.

68. The system or method of claim 67, wherein the solid electrolyte of the electrochemical cell is in the form of a container located within a second container that contains the second electrode.

69. The system or method of any one of claims 31-68, wherein the second electrode comprises a porous electronically conductive material capable of initiating and / or catalyzing anion oxidation.

70. The system or method of any one of claims 31-69, wherein the second electrode comprises a nickel foam.

71. The system or method of any one of claims 31-70, wherein the metallic alkali metal of the first electrode, the alkali metal-containing material, the alkali metal ions, the#14431536vlproduced metallic metal, and / or the alkali metal of the anodic reactant comprise the same metal.

72. The system or method cell of any one of claims 31-71, wherein the electrochemical cell is a battery.

73. The system or method of claim 72, wherein the battery is a rechargeable battery.

74. A method, comprising: receiving a metallic metal from a location that is remote from a primary site; and oxidizing the metallic metal to produce oxidized product and energy at the primary site; wherein oxidizing comprises discharging an alkali metal fuel cell to produce an electric current; wherein the alkali metal fuel cell comprises: a cathode comprising a cathodic reactant comprising gaseous oxygen, gaseous water, and / or gaseous carbon dioxide; and an anode comprising an anodic reactant comprising the metallic metal.

75. The method of claim 74, wherein the metallic metal of the anodic reactant is liquid alkali metal.

76. The method of any one of claims 74-75, wherein: the cathodic reactant comprises gaseous water; the alkali metal fuel cell produces a discharge product comprising an alkali metal hydroxide during the discharging; and at least a portion of the alkali metal hydroxide is in the form of a liquid solution.

77. The method of any one of claims 74-76, wherein: the alkali metal fuel cell comprises a solid electrolyte; and#14431536vlthe solid electrolyte is below the anode and the cathode is below the solid electrolyte in the direction of gravitational pull.

78. The method of any one of claims 74-77, wherein: the anodic reactant comprises a layer of the liquid alkali metal; and the layer of liquid alkali metal has a thickness of greater than or equal to 1 millimeter and less than or equal to 5 centimeters.

79. The method of any one of claims 74-78, wherein: the anodic reactant comprises a layer of the liquid alkali metal; and the liquid alkali metal is not replenished during the discharging.

80. The method of any one of claims 74-79, further comprising transporting the oxidized product to a secondary site that is remote from the primary site.

81. The method of claim 80, wherein the location that is remote from the primary site is the same as the secondary site that is remote from the primary site.

82. The method of any one of claims 74-81, wherein the location is at least 5 miles away from the primary site.

83. The method of any one of claims 74-82, wherein the location is at least 10 miles away from the primary site.

84. The method of any one of claims 74-83, wherein the location is at least 100 miles away from the primary site.

85. The method of any one of claims 74-84, wherein the location is at least 1000 miles away from the primary site.#14431536vl86. The method of any one of claims 80-85, wherein the secondary site is at least 5 miles away from the primary site.

87. The method of any one of claims 80-86, wherein the secondary site is at least 10 miles away from the primary site.

88. The method of any one of claims 80-87, wherein the secondary site is at least 100 miles away from the primary site.

89. The method of any one of claims 80-88, wherein the secondary site is at least 1000 miles away from the primary site.

90. The method of any one of claims 80-89, wherein the cost of electricity at the secondary site is lower than the cost of electricity at the primary site at the time the oxidized product is shipped from the primary site to the secondary site and / or at the time the oxidized product is received at the secondary site from the primary site.

91. The method of any one of claims 80-90, wherein the cost of electricity at the secondary site is at least 5% lower than the cost of electricity at the primary site at the time the oxidized product is shipped from the primary site to the secondary site and / or at the time the oxidized product is received at the secondary site from the primary site.

92. The method of any one of claims 80-91, wherein the cost of electricity at the secondary site is at least 10% lower than the cost of electricity at the primary site at the time the oxidized product is shipped from the primary site to the secondary site and / or at the time the oxidized product is received at the secondary site from the primary site.

93. The method of any one of claims 80-92, wherein the cost of electricity at the secondary site is at least 20% lower than the cost of electricity at the primary site at the time the oxidized product is shipped from the primary site to the secondary site and / or at the time the oxidized product is received at the secondary site from the primary site.#14431536vl94. The method of any one of claims 80-93, wherein the cost of electricity at the secondary site is at least 50% lower than the cost of electricity at the primary site at the time the oxidized product is shipped from the primary site to the secondary site and / or at the time the oxidized product is received at the secondary site from the primary site.

95. The method of any one of claims 74-94, wherein the cost of electricity at the location that is remote from the primary site is lower than the cost of electricity at the primary site at the time the metallic metal is shipped from the location that is remote from the primary site to the primary site and / or at the time the metallic metal is received at the primary site from the location that is remote from the primary site.

96. The method of any one of claims 74-95, wherein the cost of electricity at the location that is remote from the primary site is at least 5% lower than the cost of electricity at the primary site at the time the metallic metal is shipped from the location that is remote from the primary site to the primary site and / or at the time the metallic metal is received at the primary site from the location that is remote from the primary site.

97. The method of any one of claims 74-96, wherein the cost of electricity at the location that is remote from the primary site is at least 10% lower than the cost of electricity at the primary site at the time the metallic metal is shipped from the location that is remote from the primary site to the primary site and / or at the time the metallic metal is received at the primary site from the location that is remote from the primary site.

98. The method of any one of claims 74-97, wherein the cost of electricity at the location that is remote from the primary site is at least 20% lower than the cost of electricity at the primary site at the time the metallic metal is shipped from the location that is remote from the primary site to the primary site and / or at the time the metallic#14431536vlmetal is received at the primary site from the location that is remote from the primary site.

99. The method of any one of claims 74-98, wherein the cost of electricity at the location that is remote from the primary site is at least 50% lower than the cost of electricity at the primary site at the time the metallic metal is shipped from the location that is remote from the primary site to the primary site and / or at the time the metallic metal is received at the primary site from the location that is remote from the primary site.

100. The method of any one of claims 74-99, wherein when the metallic metal is received from the location that is remote from the primary site, greater than or equal to 10 kilograms of the metallic metal is received.

101. The method of any one of claims 74-100, wherein when the metallic metal is received from the location that is remote from the primary site, the metallic metal is not contained within a battery or other electrochemical cell.

102. The method of any one of claims 74-101, wherein the metallic metal comprises metallic aluminum, metallic magnesium, metallic silicon, metallic calcium, metallic titanium, metallic gallium, and / or a metallic alkali metal.

103. The method of any one of claims 74-102, wherein the metallic metal is a metallic alkali metal.

104. The method of any one of claims 74-103, wherein the metallic metal is metallic sodium.

105. The method of any one of claims 74-103, wherein the metallic metal is metallic lithium.#14431536vl106. The method of any one of claims 74-103, wherein the metallic metal is metallic potassium.

107. The method of any one of claims 74-106, wherein the method further comprises producing the metallic metal from a metal hydroxide, a metal oxide, a metal peroxide, a metal carbonate, a metal bicarbonate, a metal oxalate, a metal peroxyoxylate, and / or a metal halide at the location that is remote from the primary site.

108. The method of any one of claims 74-107, wherein the method further comprises producing the metallic metal from an alkali metal hydroxide, an alkali metal oxide, an alkali metal peroxide, an alkali metal carbonate, an alkali metal bicarbonate, an alkali metal oxalate, an alkali metal peroxyoxylate, and / or an alkali metal halide at the location that is remote from the primary site.

109. The method of claim 6, wherein the metallic metal is an alkaline earth metal.

110. The method of claim 109, wherein the alkaline earth metal is magnesium or calcium.#14431536vl

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