Metal-mediated ammonia production and systems for performing the same

Abstract

Described herein are electrochemical methods for producing ammonia. In one aspect, the methods involve introducing nitrogen gas at a pressure higher than ambient pressure into an electrochemical cell comprising an electrolyte composition and applying a current to the electrochemical cell to convert the nitrogen gas to ammonia. In one aspect, the electrolyte composition comprises (i) an organic solvent, (ii) a proton donor, and (iii) a salt of lithium, calcium, magnesium, strontium, yttrium, scandium, zirconium, or any combination thereof. The methods described herein provide increased Faraday efficiency (FE) of ammonia while using less energy (i.e., applied current).

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit and priority of co-pending U.S. Provisional Patent Application No. 63 / 537,336, filed September 8, 2023, and co-pending U.S. Provisional Patent Application No. 63 / 602,293, filed November 22, 2023, the contents of which are incorporated herein by reference in their entirety. Background Technology

[0003] Ammonia plays a vital role in agriculture as a fertilizer, and its potential as a carrier of renewable energy is increasingly recognized due to its high hydrogen content and energy density. Current methods for ammonia production (i.e., the Haber-Bosch process) are characterized by high energy demands, requiring extremely high temperatures and pressures ranging from 350°C to 450°C and from 100 bar to 200 bar, respectively. Furthermore, this conventional method, reliant on fossil fuels, is only economically feasible in large, centralized plants. However, with the decreasing cost of renewable electricity, interest is growing in electrochemical methods for ammonia production. These methods offer the potential for distributed production from intermittent renewable energy sources, along with the additional benefits of zero CO2 emissions and lower capital costs.

[0004] Although numerous nitrogen reduction systems in aqueous media with different configurations and catalyst compositions have been proposed, their widespread use is impractical due to low Faraday efficiency (FE) and productivity caused by competing HERs. Furthermore, nitrogen has lower solubility in aqueous solutions compared to organic solutions. Additionally, systems with very low FE and partial current densities face challenges related to ammonia contamination, making reproducibility more difficult. Summary of the Invention

[0005] This paper describes an electrochemical method for producing ammonia. In one aspect, the method involves introducing nitrogen gas at a pressure higher than ambient pressure into an electrochemical cell containing an electrolyte composition and applying an electric current to the electrochemical cell to convert the nitrogen gas into ammonia. In one aspect, the electrolyte composition comprises (i) an organic solvent, (ii) a proton donor, and (iii) a salt of lithium, calcium, magnesium, strontium, yttrium, scandium, zirconium, or any combination thereof. The method described herein provides an increased ammonia Faraday efficiency (FE) while using less energy (i.e., the applied current).

[0006] Other systems, methods, features, and advantages of this disclosure will be apparent or become apparent to those skilled in the art upon review of the following figures and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, within the scope of this disclosure, and protected by the appended claims. Furthermore, all optional and preferred features and modifications of the described embodiments can be used in all aspects of the disclosure taught herein. Moreover, the various features of the dependent claims and all optional and preferred features and modifications of the described embodiments can be combined and interchanged with each other. Attached Figure Description

[0007] Many aspects of this disclosure can be better understood with reference to the following accompanying drawings. The components in the drawings are not necessarily drawn to scale, but rather the emphasis is on clearly illustrating the principles of this disclosure. Furthermore, in the drawings, the same reference numerals denote corresponding parts in multiple views.

[0008] Figure 1A to Figure 1B The benchmark test experiments are shown. (A) The change of NH3FE with applied current density. (B) The change of NH3CD with applied current density.

[0009] Figure 2A to Figure 2B The figures show the pressure variations of (A) NH3 FE and (B) NH3 CD. Current density is at −150 mA / cm². 2 With 0 mA / cm 2 The process alternates between two time periods, each lasting 2 minutes. 2M LiClO4 is dissolved in THF containing 0.065M EtOH.

[0010] Figure 3A to Figure 3F The effects of proton donor concentration are shown: (A) NH3 FE versus EtOH concentration at 20 bar; (B) NH3 CD versus EtOH concentration at 20 bar; (C) NH3 FE versus EtOH concentration at 50 bar; (D) NH3 CD versus EtOH concentration at 50 bar; (E) NH3 FE versus EtOH concentration at 100 bar; (F) NH3 CD versus EtOH concentration at 100 bar. Current density is at −150 mA / cm². 2 With 0 mA / cm 2 The process alternates between these two time periods, each lasting 2 minutes. 2M LiClO4 is dissolved in THF containing EtOH.

[0011] Figure 4A to Figure 4BThe effect of alkyl chain length on the proton donor is shown. (A) NH3 FE varies with different proton donors. (B) NH3 CD varies with different proton donors. Current density is at −150 mA / cm². 2 With 0 mA / cm 2 The process alternates between two time periods, each lasting 2 minutes. 2M LiClO4 is dissolved in THF containing 0.1M proton donor. The N2 pressure is set to 20 bar.

[0012] Figure 5A to Figure 5B The effect of Li salt concentration is shown. (A) NH3 FE versus LiBF4 concentration. (B) NH3 CD versus LiBF4 concentration. Current density is in the range of −150 mA / cm². 2 With 0 mA / cm 2 Switch between these two time periods, each lasting 2 minutes. Dissolve LiBF4 in THF containing 0.065 M EtOH. Set the N2 pressure to 20 bar.

[0013] Figure 6A to Figure 6D Different efficiencies (EE - energy efficiency, VE - voltage efficiency, and FE - Faraday efficiency) are shown. (A) Efficiency varies with applied current density. (B) Efficiency varies with pressure. (C) Efficiency varies with EtOH concentration at 20 bar. (D) Efficiency varies with LiBF4 concentration.

[0014] Figure 7 The effect of the proton source on voltage efficiency is shown. Voltage efficiency versus cell potential, for LiMAS with various proton sources such as H2O, H2, and EtOH.

[0015] Figure 8A to Figure 8B The table shows estimates of capital expenditure (CapEx) and operating expenditure (OpEx). (A) Total CapEx cost of the LiMAS plant for different NH3 current densities in the high-voltage electrochemical cell. The CapEx estimate includes the cost of the electrolyzer based on the autoclave and auxiliary equipment such as air separators, compressors, heat exchangers, transformers, coolers, etc. (B) Total OpEx cost of the LiMAS plant varying with the cell voltage of the electrochemical cell. OpEx cost includes the electricity consumption of the electrochemical cell and utilities used to operate the auxiliary equipment.

[0016] Figure 9A to Figure 9D The diagram shows (A) a schematic diagram and structure of a batch autoclave for electrochemical ammonia synthesis; (B) NH3 FE and NH3 CD under different applied current densities (CD); and (C) NH3 FE and NH3 CD under different current densities.14 N experiment 1 H-NMR spectrum; and (D) −15 mA / cm 2 Below 15 N experiment 1 H-NMR spectrum.

[0017] Figure 10A to Figure 10D The following images are shown: (A) SEM image of Ni foam deposited by Ca after electrolysis; (B) EDS spectrum of the electrode after electrolysis, showing the presence of Ca and Ni; (C) high-resolution XPS scan of the electrode after electrolysis, confirming the presence of Ca; and (D) XPS full-spectrum scan of the electrode after electrolysis, showing the presence of O from perchlorate material.

[0018] Figure 11A to Figure 11B A representative chronopotentiometry method is shown. (A) The applied current density, total cell potential, and charge change over time. The current density is in the range of −30 mA / cm². 2 With 0 mA / cm 2 Switching between these states, the total charge passing through is approximately 110 C. (B) The magnified version clearly shows the applied current density, cell potential, and charge.

[0019] Figure 12A to Figure 12B The figures (A) show NH3 under different applied CD and (B) NH3 under different applied CD.

[0020] Figure 13A to Figure 13B A comparison of NH3 FE and NH3 CD for LiMAS, MgMAS, and CaMAS is shown.

[0021] Figure 14A to Figure 14B The NMR spectra of (A) the post-electrolyte and pre-electrolyte in the control experiment at 6 bar Ar are shown, and the NMR spectra of (B) the post-electrolyte and pre-electrolyte in the open-circuit control experiment after the freshly prepared electrolyte was kept open for 2 hours in a fume hood.

[0022] Figure 15A to Figure 15B (A) shows the experiments for different current densities. 1 (B) H-NMR spectra and NMR calibration curves at different current density points.

[0023] Figure 16A to Figure 16DThe following images are shown: (A) SEM image of Ni foam deposited with Mg after electrolysis; (B) EDS spectrum of the electrode after electrolysis, showing the presence of Mg and Ni; (C) High-resolution XPS scan of the electrode after electrolysis, confirming the presence of Mg. 0 The presence of (1s) and high-resolution XPS scanning of the electrode after (D) electrolysis confirmed the presence of Mg. 0 The existence of (2p).

[0024] Figure 17 An exemplary electrochemical cell described herein is shown.

[0025] Figure 18 An exemplary system for the continuous production of ammonia using the method described herein is shown.

[0026] Further advantages of the invention will be set forth in part in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and obtained by means of the elements and combinations particularly pointed out in the appended claims. It should be understood that the foregoing general description and the following detailed description are merely exemplary and explanatory, and do not limit the claimed invention. Detailed Implementation

[0027] Benefiting from the teachings presented in the foregoing description and related drawings, those skilled in the art will conceive of numerous modifications and other embodiments disclosed herein. Therefore, it should be understood that this disclosure is not limited to the specific embodiments disclosed, and that modifications and other embodiments are intended to be included within the scope of the appended claims. Those skilled in the art will recognize many variations and adaptive modifications to the aspects described herein. These variations and adaptive modifications are intended to be included in the teachings of this disclosure and are covered by the claims herein.

[0028] Although specific terms are used in this article, they are used only in a general and descriptive sense and not for limiting purposes.

[0029] Those skilled in the art will understand upon reading this disclosure that each individual embodiment described and illustrated herein has discrete components and features that can be readily separated from or combined with features of any of the other several embodiments without departing from the scope or spirit of this disclosure.

[0030] Any described method may be performed in the order of the described events or in any other logically possible order. That is, unless expressly stated otherwise, it is not intended to interpret any method or aspect set forth herein as requiring its steps to be performed in a particular order. Therefore, where a method claim does not specifically state in the claims or specification that the steps are limited to a particular order, no inference is ever made in any respect. This applies to any possible non-expressive basis for interpretation, including matters concerning the logic of the arrangement of steps or the flow of operations, the general meaning derived from grammatical organization or punctuation, or the number or type of aspects described in the specification.

[0031] All disclosures mentioned herein are incorporated by reference in connection with the disclosure and description of these methods and / or materials. The publications discussed herein are provided only for informational purposes prior to the filing date of this application. Nothing herein should be construed as an admission that the invention is not entitled to precede such publications by virtue of prior invention. Furthermore, the dates of the publications provided herein may differ from the actual publication dates, which may require independent verification.

[0032] While aspects of this disclosure may be described and claimed in specific statutory categories (such as the systems statutory category), this is for convenience only, and those skilled in the art will understand that aspects of this disclosure may be described and claimed in any statutory category.

[0033] It should also be understood that the terminology used herein is for descriptive purposes only and is not intended to be restrictive. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosed compositions and methods pertain. It should be further understood that terms such as those defined in commonly used dictionaries should be interpreted as having meanings consistent with their meanings in the context of the specification and the relevant field, and should not be interpreted in an idealized or overly formal sense unless expressly defined herein.

[0034] Before describing various aspects of this disclosure, the following definitions are provided and should be used unless otherwise indicated. Other terms may be defined elsewhere in this disclosure.

[0035] definition

[0036] As used herein, “comprising” should be interpreted as specifying the presence of the referred feature, integer, step, or component, but does not preclude the presence or addition of one or more features, integers, steps, or components or groups thereof. Furthermore, each of the terms “through,” “comprising / comprise / comprised of,” “including / includes / included,” “involving / involves / involved,” and “such as” is used in its open, non-restrictive sense and may be used interchangeably. Additionally, the term “comprising” is intended to include instances and aspects covered by the terms “substantially constitutes…” and “consisting of…”. Similarly, the term “substantially constitutes…” is intended to include instances covered by the term “consisting of…”.

[0037] As used in the specification and appended claims, the singular forms “an,” “a,” and “the” include plural indicators unless the context clearly specifies otherwise. Thus, for example, references to “solvent” include, but are not limited to, mixtures or combinations of two or more such solvents.

[0038] It should be understood that ratios, concentrations, amounts, and other numerical data may be expressed in ranges herein. It will be further understood that the endpoints of each in a range are important both in relation to and independent of the other endpoint. It should also be understood that many values ​​are disclosed herein, and each value is also disclosed herein as “about” to that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. In this document, a range may be expressed as from “about” one particular value and / or to “about” another particular value. Similarly, when a value is expressed as an approximation, it will be understood, by using the antecedent “about,” that the particular value forms on the other hand. For example, if the value “about 10” is disclosed, then “10” is also disclosed.

[0039] When indicating a range, on the other hand, it includes a range from one specific value and / or to another specific value. For example, when the stated range includes one or two limits, the range excluding one or both of these included limits is also included in this disclosure; for example, the phrase "x to y" includes a range from 'x' to 'y' as well as a range greater than 'x' and less than 'y'. The range can also be expressed as an upper limit, such as 'about x, y, z or less' and should be interpreted as including the specific ranges of 'about x', 'about y', and 'about z' as well as the ranges of 'less than x', 'less than y', and 'less than z'. Similarly, the phrase 'about x, y, z or greater' should be interpreted as including the specific ranges of 'about x', 'about y', and 'about z' as well as the ranges of 'greater than x', 'greater than y', and 'greater than z'. Additionally, the phrase "about 'x' to 'y'", where 'x' and 'y' are numerical values, includes "about 'x' to about 'y'".

[0040] It should be understood that this range format is used for convenience and brevity, and therefore should be interpreted flexibly to include not only the values ​​explicitly listed as range boundaries, but also all individual values ​​or subranges covered within that range, as if each value and subrange were explicitly listed. For example, the numerical range “about 0.1% to 5%” should be interpreted to include not only the explicitly listed values ​​of about 0.1% to about 5%, but also individual values ​​(e.g., about 1%, about 2%, about 3%, and about 4%) and subranges (e.g., about 0.5% to about 1.1%; about 5% to about 2.4%; about 0.5% to about 3.2%, and about 0.5% to about 4.4%, and other possible subranges) within the specified range. Thus, for example, if the amount of the component is about 1%, 2%, 3%, 4%, or 5%, where any value can be the lower or upper endpoint of the range, then any range between 1% and 5% (e.g., 1% to 3%, 2% to 4%, etc.) is considered.

[0041] As used herein, the terms “about,” “approximately,” “equal to or about,” and “substantially” mean that the quantity or value in question may be an exact value or a value that provides an equivalent result or effect to that stated in the claims or taught herein. That is, it should be understood that quantities, dimensions, formulations, parameters, and other quantities and characteristics are not and not necessarily exact, but may be approximate and / or larger or smaller as needed to reflect tolerances, conversion factors, rounding, measurement errors, and other factors known to those skilled in the art, resulting in an equivalent result or effect. In some cases, it is not reasonable to determine a value that provides an equivalent result or effect. In such cases, it is generally understood that, as used herein, “about” and “equal to or about” mean a variation of ±10% of the indicated nominal value, unless otherwise indicated or inferred. Generally, quantities, dimensions, formulations, parameters, or other quantities or characteristics are “about,” “approximately,” or “equal to or about,” whether or not explicitly stated so. It should be understood that where “about,” “approximately,” or “equal to or about” is used before a quantitative value, unless otherwise specifically stated, the parameter also includes the specific quantitative value itself.

[0042] As used herein, the term "alkyl" refers to a branched or unbranched saturated hydrocarbon group having 1 to 25 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, hexyl, heptyl, octyl, decyl, tetradecyl, hexadecyl, eicosyl, tetracosyl, etc. Examples of longer-chain alkyl groups include, but are not limited to, palmitate groups. "Lower alkyl" groups are alkyl groups containing one to six carbon atoms.

[0043] As used herein, the term "cycloalkyl" refers to a non-aromatic carbon-based ring consisting of at least three carbon atoms. Examples of cycloalkyl groups include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, etc.

[0044] As used herein, the term "aryl" refers to a group containing any carbonyl aromatic group, including but not limited to benzene, naphthalene, phenyl, biphenyl, anthracene, etc. Aryl groups can be substituted or unsubstituted. An aryl group can be substituted by one or more groups, including but not limited to alkyl, cycloalkyl, alkoxy, alkenyl, cycloalkenyl, alkynyl, cycloalkynyl, aryl, heteroaryl, aldehyde, -NH2, carboxylic acid, ester, ether, halide, hydroxyl, ketone, azide, nitro, silyl, sulfonyl-oxo, or thiol. The term "biaryl" is a specific type of aryl group and is included in the definition of "aryl." Additionally, aryl groups can be monocyclic or contain polycyclic structures, which are fused ring structures or linked by one or more bridging groups (such as carbon-carbon bonds). For example, a biaryl group refers to two aryl groups linked together by a fused ring structure, as in naphthalene, or two aryl groups linked by one or more carbon-carbon bonds, as in biphenyl. Fused aryl groups, including but not limited to indene and naphthalene groups, are also considered.

[0045] As used herein, the term "salt" is defined as the dry solid form of a water-soluble compound having both cations and anions. When a salt is added to water, it dissociates into cations and anions.

[0046] As used herein, for convenience, multiple (i.e., more than one) items, structural elements, constituent elements, and / or materials may be presented in a common list. However, these lists should be interpreted as if each part of the list were separately identified as a separate and distinct part. Therefore, without indication to the contrary, a single part of any such list should not be construed as substantially equivalent to any other part of the same list based solely on its presentation in a common group.

[0047] Concentration, quantity, and other numerical data may be expressed or presented in range format herein. It should be understood that such range format is used solely for convenience and brevity, and therefore should be flexibly interpreted to include not only the numerical values ​​explicitly stated as the limits of the range, but also all individual numerical values ​​or subranges encompassed within that range, as if each numerical value and subrange were explicitly stated. As an example, the numerical range “about 1” to “about 5” should be interpreted to include not only the explicitly stated values ​​of about 1 to about 5, but also the individual values ​​and subranges within the indicated range. Thus, the numerical range includes individual values ​​such as 2, 3, and 4, and subranges such as 1-3, 2-4, 3-5; about 1 to about 3, 1 to about 3, about 1 to 3, etc., and individually 1, 2, 3, 4, and 5. The same principle applies to ranges that list only one numerical value as a minimum or maximum value. Furthermore, this interpretation should apply regardless of the width or range of the characteristic being described.

[0048] The disclosed materials and components can be used in, in combination with, the disclosed compositions and methods, in the preparation of the disclosed compositions and methods, or as products of the disclosed compositions and methods. These and other materials are disclosed herein, and it should be understood that when combinations, subsets, interactions, groups, etc., of these materials are disclosed, although specific references to the various individual and collective combinations and arrangements of these compounds may not be explicitly disclosed, each is specifically considered and described herein. For example, if a class of molecules A, B, and C and a class of molecules D, E, and F are disclosed, and an example of the combination A + D is disclosed, then each is considered individually and in combination, even if not individually listed. Thus, in this example, each of the combinations A + E, A + F, B + D, B + E, B + F, C + D, C + E, and C + F is specifically considered and should be considered as disclosed according to the combination of: A, B, and C; D, E, and F; and exemplary combinations of A + D. Similarly, any subsets or combinations of these combinations are also specifically considered and disclosed. Therefore, for example, subgroups of A + E, B + F, and C + E are specifically considered and should be considered as disclosed according to combinations of the following: A, B, and C; D, E, and F; and exemplary combinations of A + D. This concept applies to all aspects of this disclosure, including but not limited to steps in methods of manufacturing and using the disclosed compositions. Therefore, if there are various additional steps that can be performed using any specific embodiment or combination of embodiments of the disclosed methods, each such combination is specifically considered and should be considered as disclosed.

[0049] Electrochemical production of ammonia

[0050] This article describes an electrochemical method for ammonia production. Despite significant advances in aqueous electrochemical ammonia synthesis, Li-mediated NH3 synthesis remains hampered by poor energy efficiency, significantly lower than the conventional Haber-Bosch process, primarily due to the high reducing electroplating potential of Li (approximately −3.04 V relative to SHE). It has been found that electrochemical ammonia production under positive nitrogen pressure improves the ammonia Faraday efficiency (FE) while using less energy (i.e., the applied current).

[0051] In one aspect, the method involves introducing nitrogen gas at a pressure higher than ambient pressure into an electrochemical cell containing an electrolyte composition and applying an electric current to the electrochemical cell to convert the nitrogen gas into ammonia. Figure 17 An exemplary electrochemical cell is depicted. (See reference...) Figure 17The electrochemical cell 1 includes a cathode 2 and an anode 3. An electrolyte composition 4 is disposed between the cathode 2 and the anode 3. The cathode 2 and the anode 3 are housed in a reaction chamber 5, which is a closed system such that a positive pressure of nitrogen can be maintained within the chamber. In one aspect, the reaction chamber contains iron, stainless steel, or any other suitable metal capable of withstanding high pressure.

[0052] The cathode and anode may contain materials typically used for electrochemical reactions. In one aspect, the anode contains nickel, platinum, tungsten, a metal alloy, a metal oxide, or graphite. In another aspect, the cathode contains steel, nickel, copper, titanium, molybdenum, or graphite.

[0053] The electrochemical cell operates under conditions that cause metal ions in the electrolyte composition to be converted into metals at cathode 2, wherein the metals subsequently react with nitrogen gas to form a metal nitride (MN). The metal nitride then reacts with protons (H+) provided by a proton donor (HA). + The reaction produces NH3, lithium ions, and a deprotonated proton donor (A). Protons (H2O) are then formed. + Protons (H) are produced by a proton donor at anode 3. + It reacts with deprotonated proton donor (A) to produce proton donor (HA).

[0054] The method described in this paper provides an energy-efficient way to produce ammonia. The only energy source required for the electrochemical cell is a voltage source. The method described in this paper does not require heat to produce ammonia. For example, the temperature in the reaction chamber is from about 25°C to about 30°C.

[0055] In some aspects, the ion-conducting membrane 6 is located between the anode 3 and the cathode 2. In one aspect, the membrane comprises porous glass or a porous polymer such as porous polyethylene or porous polypropylene. In one aspect, the ion-conducting membrane is a Daramic™ porous polymer separator (Polypore International Inc., Charlotte, North Carolina, USA).

[0056] In one aspect, when using an ion-conducting membrane, the electrolyte composition can be first added to the anode chamber (i.e., the space between the anode 3 and the ion-conducting membrane 6) and then added to the cathode chamber (i.e., the space between the cathode 2 and the ion-conducting membrane 6).

[0057] The electrochemical cell also includes a voltage source 7 connecting the cathode to the anode. In one aspect, a voltage source, such as a DC power supply or a solar energy device for power generation, is connected to the anode and cathode via a conductive wire 8 to supply energy for operating the electrochemical cell. In one aspect, the conductive wire is made of copper. In one aspect, the voltage source can apply a current density of approximately −200 mA / cm². 2To approximately 2,500 mA / cm 2 The current. In another aspect, a voltage source can apply a current density of −200 mA / cm². 2 0 mA / cm 2 225 mA / cm 2 500 mA / cm 2 750 mA / cm 2 1,000 mA / cm 2 1,250 mA / cm 2 1,500 mA / cm 2 1,750 mA / cm 2 2,000 mA / cm 2 2,250 mA / cm 2 or 2,500 mA / cm 2 The current, where any value can be the lower and upper limits of the range (e.g., 500 mA / cm). 2 Up to 1,750 mA / cm 2 The voltage source can be turned on and off as needed.

[0058] In some respects, the current can be applied to the electrochemical cell in an alternating manner. In one respect, (i) the current is applied for a first time period, (ii) the current is turned off for a second time period, and (iii) the current is applied for a third time period. In another respect, the current can be varied throughout the reaction.

[0059] The electrolyte composition introduced into the electrochemical cell comprises (i) an organic solvent, (ii) a proton donor, and (iii) a salt of lithium, calcium, magnesium, strontium, yttrium, scandium, zirconium, or any combination thereof, located between the anode and cathode.

[0060] In one aspect, the salts of lithium, calcium, magnesium, strontium, yttrium, scandium, or zirconium are tetrafluoroborate, hexafluoroarsenate hexafluorophosphate, perchlorate, trifluoromethanesulfonate, bis(oxalate)borate, difluorooxalateborate, trifluorosulfonylimide salts, or halide salts. The concentration of the salt can vary depending on its solubility in an organic solvent. In one aspect, the concentration of the salts of lithium, calcium, magnesium, strontium, yttrium, scandium, or zirconium in the electrolyte composition is from about 0.5 M to about 4.0 M. In another aspect, the concentrations of the salts of lithium, calcium, magnesium, strontium, yttrium, scandium, or zirconium are from about 0.5 M, 1.0 M, 1.5 M, 2.0 M, 2.5 M, 3.0 M, 3.5 M, or 4.0 M, wherein any value can be the lower or upper end of a range (e.g., 1.0 M to 2.5 M).

[0061] The proton donor can be any compound or material that electrochemically generates protons. In one aspect, the proton donor is an alcohol. In one aspect, the alcohol is a monohydroxy compound or a polyhydroxy compound (i.e., two or more hydroxyl groups). In another aspect, the proton donor is an alkyl alcohol, an aryl alcohol, or a cycloalkyl alcohol. In another aspect, the proton donor is a C1 to C7 alkyl alcohol. In another aspect, the proton donor is ethanol. In one aspect, the concentration of the proton donor in the electrolyte composition is from about 0.01 M to about 0.40 M. In another aspect, the concentration of the proton donor in the electrolyte composition is about 0.01 M, 0.05 M, 0.10 M, 0.15 M, 0.20 M, 0.25 M, 0.30 M, 0.35 M, or 0.40 M, wherein any value can be the lower end and upper end of a range (e.g., 0.05 M to 0.25 M).

[0062] The organic solvent can be any solvent that dissolves salts of lithium, calcium, magnesium, strontium, yttrium, scandium, or zirconium. In one aspect, the solvent includes ethers, such as, for example, dimethyl ether, diethyl ether, diethylene glycol dimethyl ether, or triethylene glycol dimethyl ether. In another aspect, the solvent includes fluorinated solvents, such as, for example, perfluoroalkanes or fluorobenzenes. In yet another aspect, the organic solvent includes tetrahydrofuran, dimethyl sulfoxide, dimethoxyethane, N,N-dimethylformamide, or any combination thereof.

[0063] In one aspect, the electrolyte composition can be introduced into the reaction chamber of an electrochemical cell through an orifice. (See reference...) Figure 17 The orifice 9 with valve 10 can be used to introduce the electrolyte composition into the reaction chamber.

[0064] The amount of nitrogen introduced into the reaction chamber can vary depending on the choice of salt and the concentration of the proton donor. In one aspect, the pressure of nitrogen in the electrochemical cell is from 1 bar to 100 bar. In another aspect, the pressure of nitrogen in the electrochemical cell is 1 bar, 2 bar, 3 bar, 4 bar, 5 bar, 6 bar, 7 bar, 8 bar, 9 bar, 10 bar, 15 bar, 20 bar, 25 bar, 30 bar, 35 bar, 40 bar, 45 bar, 50 bar, 55 bar, 60 bar, 65 bar, 70 bar, 75 bar, 80 bar, 85 bar, 90 bar, 95 bar, or 100 bar, where any value can be at the lower or upper end of the range (e.g., 5 bar to 25 bar). In one aspect, nitrogen can be introduced into the reaction chamber of the electrochemical cell through an orifice. (See reference...) Figure 17 The orifice 11 with valve 12 can be used to introduce nitrogen gas into the reaction chamber. In another aspect, the reaction chamber can be equipped with a pressure gauge for measuring the pressure inside the reaction chamber.

[0065] In one aspect, the electrolyte composition comprises a calcium salt and the proton donor comprises ethanol, and the nitrogen pressure in the electrochemical cell is 1 bar to 10 bar. In another aspect, the electrolyte composition comprises calcium perchlorate and the proton donor comprises ethanol, and the nitrogen pressure in the electrochemical cell is 1 bar to 10 bar. In yet another aspect, the electrolyte composition comprises calcium perchlorate, the proton donor comprises ethanol, the organic solvent comprises dimethoxymethane, and the nitrogen pressure in the electrochemical cell is 1 bar to 10 bar. In yet another aspect, the electrolyte composition comprises a calcium salt, the proton donor comprises ethanol, the nitrogen pressure in the electrochemical cell is 1 bar to 10 bar, and the current density applied to the electrochemical cell is about −5 mA / cm². 2 Approximately −45 mA / cm 2 .

[0066] In one aspect, the electrolyte composition comprises a magnesium salt and the proton donor comprises ethanol, and the nitrogen pressure in the electrochemical cell is 1 bar to 10 bar. In another aspect, the electrolyte composition comprises magnesium perchlorate and the proton donor comprises ethanol, and the nitrogen pressure in the electrochemical cell is 1 bar to 10 bar. In yet another aspect, the electrolyte composition comprises magnesium perchlorate, the proton donor comprises ethanol, the organic solvent comprises N,N-dimethylformamide, and the nitrogen pressure in the electrochemical cell is 1 bar to 10 bar. In yet another aspect, the electrolyte composition comprises a magnesium salt, the proton donor comprises ethanol, the nitrogen pressure in the electrochemical cell is 1 bar to 10 bar, and the current density applied to the electrochemical cell is about −40 mA / cm². 2 Approximately −20 mA / cm 2 .

[0067] In one aspect, the electrolyte composition comprises a lithium salt and the proton donor comprises ethanol, and the nitrogen pressure in the electrochemical cell is from 1 bar to 100 bar. In another aspect, the electrolyte composition comprises lithium perchlorate, the proton donor comprises ethanol, and the nitrogen pressure in the electrochemical cell is from 1 bar to 100 bar. In yet another aspect, the electrolyte composition comprises lithium perchlorate, the proton donor comprises ethanol, the organic solvent comprises tetrahydrofuran, and the nitrogen pressure in the electrochemical cell is from 1 bar to 100 bar. In yet another aspect, the electrolyte composition comprises a lithium salt, the proton donor comprises ethanol, the nitrogen pressure in the electrochemical cell is from 1 bar to 100 bar, and the current density applied to the electrochemical cell is about −150 mA / cm². 2 Approximately 600 mA / cm 2 .

[0068] The method described herein can be carried out using either a batch method or a continuous method. In one aspect, the method can be carried out using a modified autoclave via a batch method. Referring to Figure 9A, an autoclave having an anode and a cathode located within the autoclave can be used to produce ammonia.

[0069] In another aspect, the electrochemical cell described herein can be incorporated into systems for the continuous production of ammonia. (See also...) Figure 18 A mixing vessel 20 containing an electrolyte composition is prepared. The vessel 20 may have an orifice for introducing the electrolyte into the vessel. The vessel 20 may be equipped with a motor to mix the electrolyte composition before it is introduced into the electrochemical cell 21. In one aspect, a compressor or other pressurizing device may be used to introduce the electrolyte composition into the electrochemical cell 21 under pressure. Separately, a nitrogen tank 22 is connected to the electrochemical cell 21 for introducing nitrogen gas into the electrochemical cell. In one aspect, a compressor or other pressurizing device may be used to introduce nitrogen gas into the electrochemical cell 21 under pressure. A voltage source 27 is also connected to the electrochemical cell 21.

[0070] After the electrolyte composition and nitrogen are introduced into the electrochemical cell, ammonia is produced. In one aspect, the ammonia and electrolyte composition can be removed from the electrochemical cell 21 and directed to a device for removing or separating ammonia from the electrolyte composition. In one aspect, a gas-liquid membrane 23 can be used to separate the ammonia from the electrolyte composition. The electrolyte composition 24 after ammonia production and separation has a reduced concentration of proton donors, in which the conjugate base of the proton donor is present. The lean electrolyte composition 24 can be regenerated such that the conjugate base of the proton donor is converted to a protonated form, making it reusable to produce additional ammonia. In one aspect, the lean electrolyte composition 24 can be fed into a proton donor regeneration system 25. In one aspect, the proton donor regeneration system 25 is an electrolytic reactor, in which oxygen and water are fed into the proton donor regeneration system 25 to convert the conjugate base of the proton donor into a proton donor. The regenerated electrolyte composition 26 can then be fed into a mixing tank 21, in which additional proton donors and / or salts can be added as needed.

[0071] aspect

[0072] Aspect 1. A method for generating ammonia, the method comprising introducing nitrogen gas at a pressure higher than ambient pressure into an electrochemical cell, wherein the electrochemical cell comprises:

[0073] Reaction chamber;

[0074] Anode and cathode, located within the reaction chamber;

[0075] A voltage source that connects the cathode to the anode;

[0076] An ion-conducting membrane, located between the cathode and the anode; and

[0077] An electrolyte composition comprising (i) an organic solvent, (ii) a proton donor, and (iii) a salt or any combination of lithium, calcium, magnesium, strontium, yttrium, scandium, and zirconium, wherein the electrolyte composition is located between the anode and the cathode.

[0078] An electric current is applied to the electrochemical cell to convert nitrogen into ammonia.

[0079] Aspect 2. The method according to aspect 1, wherein the pressure of the nitrogen gas in the electrochemical cell is from 1 bar to 100 bar.

[0080] Aspect 3. The method according to aspect 1 or 2, wherein the salt of lithium, calcium, magnesium, strontium, yttrium, scandium or zirconium is tetrafluoroborate, hexafluorophosphate hexafluoroarsenate, perchlorate, trifluoromethanesulfonate, bis(oxalate)borate, difluorooxalateborate, trifluorosulfonylimide salt or halide salt.

[0081] Aspect 4. The method according to any one of Aspects 1 to 3, wherein the concentration of the lithium, calcium, magnesium, strontium, yttrium, scandium or zirconium salt in the electrolyte composition is from about 0.5 M to about 4.0 M.

[0082] Aspect 5. The method according to any one of Aspects 1 to 4, wherein the proton donor comprises an alcohol.

[0083] Aspect 6. The method according to any one of Aspects 1 to 4, wherein the proton donor comprises an alkyl alcohol, an aryl alcohol, or a cycloalkyl alcohol.

[0084] Aspect 7. The method according to any one of Aspects 1 to 4, wherein the proton donor comprises a C1 to C7 alkyl alcohol.

[0085] Aspect 8. The method according to any one of Aspects 1 to 4, wherein the proton donor comprises ethanol.

[0086] Aspect 9. The method according to any one of Aspects 1 to 8, wherein the concentration of the proton donor in the electrolyte composition is from about 0.01 M to about 0.40 M.

[0087] Aspect 10. The method according to any one of Aspects 1 to 9, wherein the organic solvent comprises an ether.

[0088] Aspect 11. The method according to aspect 10, wherein the ether comprises dimethyl ether, diethyl ether, diethylene glycol dimethyl ether or triethylene glycol dimethyl ether.

[0089] Aspect 12. The method according to any one of Aspects 1 to 9, wherein the organic solvent comprises a fluorinated solvent.

[0090] Aspect 13. The method according to aspect 12, wherein the fluorinated solvent comprises a perfluoroalkane or a fluorobenzene.

[0091] Aspect 14. The method according to any one of Aspects 1 to 9, wherein the organic solvent comprises tetrahydrofuran, dimethyl sulfoxide, dimethoxyethane, N,N-dimethylformamide, or any combination thereof.

[0092] Aspect 15. The method according to any one of aspects 1 to 14, wherein the current density of the current applied to the electrochemical cell is about −200 mA / cm². 2 To approximately 2,500 mA / cm 2 .

[0093] Aspect 16. The method according to aspect 1, wherein the electrolyte composition comprises a calcium salt and the proton donor comprises ethanol, and the pressure of nitrogen in the electrochemical cell is from 1 bar to 10 bar.

[0094] Aspect 17. The method according to aspect 16, wherein the calcium salt is calcium perchlorate.

[0095] Aspect 18. The method according to aspect 16 or 17, wherein the organic solvent comprises dimethoxymethane.

[0096] Aspect 19. The method according to any one of aspects 16 to 18, wherein the current density of the current applied to the electrochemical cell is about -5 mA / cm². 2 Approximately -45 mA / cm 2 .

[0097] Aspect 20. The method according to aspect 1, wherein the electrolyte composition comprises a magnesium salt, the proton donor comprises ethanol, and the pressure of nitrogen in the electrochemical cell is from 1 bar to 10 bar.

[0098] Aspect 21. The method according to aspect 20, wherein the magnesium salt is magnesium perchlorate.

[0099] Aspect 22. The method according to aspect 20 or 21, wherein the organic solvent comprises N,N-dimethylformamide.

[0100] Aspect 23. The method according to any one of aspects 20 to 22, wherein the current density of the current applied to the electrochemical cell is about -40 mA / cm². 2 Approximately -20 mA / cm 2 .

[0101] Aspect 24. The method according to aspect 1, wherein the electrolyte composition comprises a lithium salt, the proton donor comprises ethanol, and the pressure of nitrogen in the electrochemical cell is from 1 bar to 100 bar.

[0102] Aspect 25. The method according to aspect 24, wherein the lithium salt is lithium perchlorate.

[0103] Aspect 26. The method according to aspect 24 or 25, wherein the organic solvent comprises tetrahydrofuran.

[0104] Aspect 27. The method according to any one of aspects 24 to 26, wherein the current density of the current applied to the electrochemical cell is about -150 mA / cm². 2 Approximately 600 mA / cm 2 .

[0105] Aspect 28. The method according to any one of Aspects 16 to 27, wherein the concentration of ethanol in the electrolyte composition is about 0.03 M to about 0.08 M.

[0106] Aspect 29. The method according to any one of Aspects 1 to 28, wherein the anode comprises nickel, platinum, tungsten, a metal alloy, a metal oxide, or graphite.

[0107] Aspect 30. The method according to any one of aspects 1 to 29, wherein the cathode comprises steel, nickel, copper, titanium, molybdenum or graphite.

[0108] Aspect 31. The method according to any one of aspects 1 to 30, wherein the ion-conducting film comprises glass or a polymer.

[0109] Aspect 32. The method according to aspect 31, wherein the polymer comprises polyethylene or polypropylene.

[0110] Aspect 33. The method according to any one of aspects 1 to 32, wherein the temperature in the reaction chamber is about 25°C to about 30°C.

[0111] Aspect 34. The method according to any one of Aspects 1 to 33, wherein (i) the current is applied for a first time period, (ii) the current is turned off for a second time period, and (iii) the current is applied for a third time period.

[0112] Aspect 35. The method according to any one of aspects 1 to 34, wherein the electrolyte composition is stirred in the electrochemical cell.

[0113] Aspect 36. The method according to any one of Aspects 1 to 35, wherein the reaction chamber comprises stainless steel.

[0114] Aspect 37. The method according to any one of Aspects 1 to 36, wherein the reaction chamber includes a first orifice for introducing the electrolyte composition into the reaction chamber and a second orifice for introducing nitrogen gas into the reaction chamber.

[0115] Aspect 38. The method according to any one of aspects 1 to 37, wherein the reaction chamber includes a pressure gauge for measuring the pressure inside the reaction chamber.

[0116] Aspect 39. The method according to any one of aspects 1 to 38, wherein the ammonia is removed from the reaction chamber after ammonia is generated.

[0117] Aspect 40. The method according to any one of aspects 1 to 39, wherein after ammonia is generated, (i) the electrolyte composition containing ammonia is removed from the reaction chamber and (ii) ammonia is removed from the electrolyte composition.

[0118] Aspect 41. The method according to aspect 40, wherein after the ammonia is removed, the electrolyte composition is regenerated and introduced into the reaction chamber.

[0119] Aspect 42. The method according to any one of aspects 1 to 41, wherein the method is carried out continuously to produce ammonia.

[0120] Example

[0121] The following examples are provided to provide those skilled in the art with a complete disclosure and description of how to manufacture and evaluate the compounds, compositions, articles, devices, and / or methods claimed herein, and are intended merely as examples of this disclosure and not to limit the scope to which the inventors believe their disclosure to fall. Efforts have been made to ensure accuracy regarding figures (e.g., amounts, temperatures, etc.), but some errors and deviations should be accounted for. Unless otherwise stated, parts are parts by weight, temperatures are in °C or ambient temperature, and pressures are...

[0122] Example 1 – Lithium System

[0123] Materials and Methods

[0124] Electrochemical Experiment

[0125] All electrochemical ammonia synthesis experiments were conducted in a 2-electrode single-chamber glass cell, which was enclosed in a custom-designed electrochemical autoclave housed in an explosion-proof enclosure. For benchmark experiments and to assess the effect of pressure, the electrolyte solution consisted of 2M LiClO4 dissolved in THF containing 0.065 M EtOH. To investigate the effect of EtOH concentration, the following solution concentrations were used: 2M LiClO4 + 0.0325 M EtOH, 2M LiClO4 + 0.0487 M EtOH, 2M LiClO4 + 0.065 M EtOH, 2M LiClO4 + 0.097 M EtOH, 2M LiClO4 + 0.13 M EtOH, 2M LiClO4 + 0.1625 M EtOH, and 2M LiClO4 + 0.325 M EtOH. Solution concentrations used to study the effects of different proton sources: 2 M LiClO4 + 0.1 M MeOH, 2 M LiClO4 + 0.1 M EtOH, 2 M LiClO4 + 0.1 M 1-PrOH, 2 M LiClO4 + 0.1 M 1-BuOH, and 2 M LiClO4 + 0.1 M 1-PeOH in THF. For experiments involving LiBF4, 0.065 M EtOH in THF was used, along with different concentrations of LiBF4 (1 M, 2 M, 3 M, 4 M). The electrolyte solution was pre-saturated with N2 at a flow rate of 200 sccm for 10 minutes using a mass flow controller. Ni foam was used as the cathode. Fresh Ni foam was used for each run and was rinsed with EtOH for 10 minutes to remove water contamination before electrochemical testing, followed by oven drying at 80°C for 20 minutes. A planar Pt anode was used. After each reaction, the mixture was sonicated in acetone for 15 min, followed by sonication in ethanol for another 15 min, and then oven-dried at 80°C for 20 min. For good electrical connection, the dried Ni foam and Pt anode were spot-welded with Cu wire and Cu strip. The single-chamber glass tank and magnetic stir bar were dried at 80°C for 1 hour. The anode and cathode were spaced approximately 1 cm apart, and the cathode surface area facing the anode was 4 cm². 2After assembling the cell in the autoclave, it was flushed 10 times with N2 directly from the gas cylinder to remove all oxygen and other atmospheric contaminants present inside the autoclave before the electrochemical experiments. It was then transferred to a glove box along with an air compressor. Finally, the pressure was increased to a maximum of 20 bar and then depressurized three times to flush away any residual atmospheric contaminants, before being filled to the desired pressure. Electrochemical experiments were then performed using a potentiostat (Biologic SP 300) with the stirring device at 700 rpm. Chorometric potentiometry was performed using a switching current strategy, with a current of −150 mA / cm². 2 2 min, followed by 0 mA / cm 2 (Resting potential in the following text) 2 min, depending on whether the WE potential needs to be increased, decreased, or stabilized. We note that all experiments were conducted at room temperature.

[0126] Colorimetric quantification of products

[0127] NH3 via the indophenol blue process 22 Using the standard addition method 11 To quantify and interpret changes in the appearance and properties of the electrolyte solution following the electrochemical reaction, the post-electrolyte sample is diluted 100-400 times with 0.1 M H₂SO₄ to reach the detection limit. After dilution, any ammonia present will be in the form of ammonium ions. The solution is then centrifuged twice for 15 minutes each to obtain a clear solution. A calibration solution is prepared using 0.01 M NH₄Cl as a stock solution and further diluted to prepare 100 µM-500 µM NH₄Cl calibration solutions in H₂SO₄. A blank solution is prepared by adding 500 µL H₂SO₄, 500 µL phenol nitroprusside, and 500 µL alkaline sodium hypochlorite. Six sample vials were each containing 400 µL of centrifuged diluted electrolyte solution, 100 µL of internal standard aqueous solution (0.1 M H₂SO₄, 100 µM-500 µM NH₄Cl in 0.1 M H₂SO₄), 500 µL of phenol nitroprusside, followed by 500 µL of alkaline sodium hypochlorite. The mixture was incubated in the dark at ambient temperature for 30 minutes. The sample color changed from colorless to blue. The absorbance of the sample was scanned as a function of wavelengths from 400 nm to 800 nm using a visible spectrometer (Genesys 30 visible spectrometer). The maximum absorbance was observed at 632 nm, and therefore 632 nm was chosen to measure the absorbance for quantification of NH₃. The ratio of the intercept to the slope represents the molar amount of ammonia in the test sample. After calculating the molar amount, the concentration and partial current density were determined.

[0128] Control experiment

[0129] To conduct Ar blank experiments, the electrolyte was presaturated with Ar instead of N2, and pumping and purging procedures were performed with Ar instead of N2 after injection into the autoclave. Electrochemical cycling experiments were conducted with almost no ammonia current. Experiments were also conducted with switching currents and standard electrolyte compositions other than 0.1 M EtOH, and no ammonia current was observed. To account for the effect of switching currents, the electrochemical runs were performed continuously for 2 hours without switching.

[0130] Energy efficiency calculation

[0131] The energy efficiency of Li-mediated ammonia synthesis is defined as the ratio between the amount of energy contained in the ammonia produced during the reaction and the total energy used by the Li-mediated system via a potentiostat.

[0132]

[0133] Where F is the Faraday constant, V is the total cell voltage, i is the NH3 current, ∆G is the Gibbs free energy of the NH3 oxidation reaction (339 kJ / mol), Q is the total charge passing through, and n is the number of electrons transferred per mole of NH3 during the reaction. Voltage efficiency is calculated using the total current instead of the NH3 current.

[0134] Results and discussion

[0135] Benchmarking LiMAS – Optimal Switching and Potential-Independent Selectivity

[0136] Benchmark experiments were conducted at 6 bar and room temperature using a two-electrode cell without separators placed in a modified autoclave apparatus. Detailed specifications of the high-voltage electrochemical cell are provided in the supporting information. Ni foam was used as the cathode, and Pt as the anode. The electrolyte consisted of 2 M LiClO4 and 0.1 M EtOH dissolved in THF. The SEI was stabilized using a current switching strategy with a 2-min run time and a 2-min rest time. The total run time was 4 h. The resting current density was maintained at 0 mA / cm². 2 (i.e., open circuit), and apply different operating current densities. NH3 is quantified by using an additive method. 11

[0137] As the applied current density (CD) increases, NH3 CD increases, while NH3 FE remains constant at approximately 15% of the average value (Figure 1A and 1B). Figure 1BThis indicates that the productivity of NH3 and H2 increases proportionally with increasing current density. It also means that the ratio of Li proton decomposition to Li3N proton decomposition rate is independent of potential. Therefore, this potential-independent behavior is likely due to the fixed fractional coverage of Li3N at the cathode, since proton decomposition is a thermochemical step. The coverage of Li3N is balanced by the nitridation and proton decomposition reactions, which in turn are directly related to N2 pressure and proton donor, respectively. In addition to these two factors, the anion of the Li salt, its concentration, and the solvent also affect the kinetics of LiMAS. Therefore, we investigate these parameters.

[0138] Switching time plays a role in stabilizing the cell voltage by maintaining the stability of the SEI. Li deposition mainly occurs during the operating time (when a negative current density is applied). Li nitridation, Li3N proton decomposition, and Li proton decomposition are rate-limiting steps. During the resting time (when the current density is zero), Li deposition ceases, and the nitridation and proton decomposition steps dominate. Li nitridation depends on the N2 pressure. Li3N proton decomposition and Li proton decomposition depend on the proton donor concentration. NH3 FE depends on both Li nitridation and Li3N proton decomposition. Therefore, we consider the N2 pressure and EtOH concentration parameters to be interdependent. A period of time is required to form a stable solid electrolyte interface (approximately 1 hour), which forms a passivation layer around the cathode, thereby preventing electrolyte oxidation. The passivation layer is only effective for Li... + Ions, N2, H2, NH3 and H + It is permeable, thus preventing THF from coming into contact with the electrode.

[0139] Switching time also affects mass transfer. Experiments have shown that during the resting time, the open-circuit potential should be close to approximately 3V (Li). + The equilibrium reduction potential (ERP) is used to stabilize SEI and NH3 formation. If the open-circuit potential becomes below 3V, Li proton decomposition favors H2 formation. Therefore, the resting time should be optimal to keep the open-circuit potential close to approximately 3V. Stirring speed also affects Li3N and Li proton decomposition, and the stirring speed may vary depending on the size and type of stirrer used. If the open-circuit potential becomes much lower than 3V, it can be restored to 3V by reducing the resting time, working time, and stirring speed. If the open-circuit potential becomes higher than 3V, it can be restored to 3V by increasing the resting time, reducing the working time, and increasing the stirring speed. Based on our observations, a 2-minute working time and a 2-minute resting time are optimal for stabilizing the SEI. At higher applied current densities, numerous oscillations exist in the total cell potential due to the generated heat, resulting in a considerable error bar. For further investigation, we used −150 mA / cm². 2The experiment also included a 2-minute working time and a 2-minute rest time, as the system oscillations were minimal and these experiments were easily conducted on a laboratory scale.

[0140] Effects of N2 pressure and proton donor concentration

[0141] To assess the effect of N2 pressure, NH3 FE and NH3 CD were measured as the N2 pressure increased from 1 bar to 100 bar at a fixed EtOH concentration of 0.065 M. Figure 2A and Figure 2B The changes in NH3 FE and CD with pressure are shown. NH3 FE gradually increases as the pressure changes from 1 bar to 15 bar, followed by a sharp increase from 15 bar to 20 bar. Beyond 20 bar, NH3 FE remains constant even when the N2 pressure is increased to a maximum of 100 bar. With increasing pressure, the solubility of N2 in the electrolyte solution increases, leading to an increased concentration of dissolved N2, which reacts with electrodeposited Li to form Li3N. Li3N then undergoes protonation with ethanol to form NH3 and Li. + The increasing pressure ensured excessive availability of Li3N. Therefore, the rate of protonation was limited by EtOH mass transfer. Thus, despite increasing the pressure to 100 bar to increase the concentrations of dissolved N2 and Li3N, the NH3 FE remained unchanged. At the optimal pressure of 20 bar, the maximum NH3 FE obtained was approximately 35%.

[0142] At pressures greater than 20 bar, the reaction is EtOH-limited (i.e., H+). + (Limited) State. It has been previously proposed that NH3 FE increases with increasing pressure and proton donor concentration. However, as shown in Figure 2, a limiting trend exists. We begin by investigating the effect of ethanol concentration at 20 bar N2 pressure. NH3 FE and CD increase with increasing ethanol concentration until a 0.065 M ethanol concentration, beyond which NH3 FE and CD decrease. The decrease in FE and CD may be related to increased Li protonation rather than Li3N protonation. The optimal ethanol concentration they observed for achieving maximum NH3 FE was 0.065 M. At higher pressures such as 50 bar and 100 bar, the trend remains unchanged, and at the optimal ethanol concentration of 0.065 M, maximum NH3 FE remains at approximately 35%. Figure 3 illustrates the effect of proton concentration on NH3 FE and NH3 CD.

[0143] Influence of proton donor type and pKa

[0144] Proton availability depends on the concentration of the proton donor and the pKa of the alcohol. To investigate the effect of pKa, different linear-chain alcohol proton sources were used in LiMAS, such as methanol (pKa = 15.5), ethanol (pKa = 15.9), 1-propanol (pKa = 16.85), 1-butanol (pKa = 17), and 1-pentanol (pKa = 16.84). The concentration of the proton source was maintained at 0.1 M and the N2 pressure was maintained at 20 bar. Figure 4 shows the variation of NH3 FE and CD with different proton sources. 1-Butanol showed the highest NH3 FE (20.762%), followed by ethanol (15.46%), 1-propanol (13.94%), 1-pentanol (11.80%), and methanol (8.98%). The variation of FE appears to follow the pKa trend. pKa also increases with increasing alkyl chain length from methanol to 1-butanol, and then decreases. The role of proton donors and their influence on NH3 FE are not well understood in the literature. Proton donors can promote NH3 FE by influencing SEI (Self-Isolation Intake) to allow optimal diffusion of N2 and proton donors to the electrode surface. In-situ analysis of SEI is needed to understand the role of proton donors in determining NH3 selectivity.

[0145] Effect of Li salt anions

[0146] The optimal conditions for maximum NH3 selectivity are 20 bar N2 pressure and 0.065 M ethanol. So far, experiments have been conducted using LiClO4 / THF electrolyte. The size of the anion in the 1:1 electrolyte changes with the Li... + The solvation structure of the ions plays an important role in the potential distribution within the electric double layer. According to the size-dependent Poisson-Boltzmann equation, increasing the size of the anion will decrease the Li... + The local density and the local electric field near the cathode. It is clear from the literature on Li metal batteries that when Li... + When the gradient and the electric field near the cathode are not high, the SEI becomes stable (i.e., non-dendritic lithium metal growth). 19 To investigate the effect of anions, we used anions from ClO4 with a size of approximately 0.24 nm. - Instead, it was changed to BF4 with a size of approximately 0.3nm. -The optimal conditions for LiMAS were tested with LiBF4 / THF electrolyte. LiBF4 was expected to provide higher performance by stabilizing the SEI. However, LiBF4 is expensive and highly sensitive to moisture. Figure 5 shows the changes in NH3 FE and NH3 CD with LiBF4 concentration. With increasing LiBF4 concentration, NH3 FE and NH3 CD increase due to stable Li deposition and increased electrolyte conductivity. A maximum NH3 FE of approximately 70% and approximately 100 mA / cm² were observed at a 3 M LiBF4 concentration. 2 The concentrations of NH3 and CD. When the concentration exceeds 3 MLiBF4, as the viscosity of the solution increases at higher concentrations, the concentrations of NH3 FE and NH3 CD decrease, thereby reducing the conductivity of the solution.

[0147] Energy efficiency of LiMAS

[0148] Energy efficiency is calculated by multiplying the Faraday efficiency and voltage efficiency for all process conditions studied above. Voltage efficiency is the ratio of the equilibrium potential of the redox reaction to the actual cell voltage. Typically, an equilibrium potential is chosen for the entire redox reaction occurring in the cell. Depending on the source of the protons, it can be one of the following redox reactions.

[0149] N2 + 3 H2 → 2 NH3E 0 = 0.057 V relative to SHE

[0150] or

[0151] N2 + 3 H2O → 2 NH3 + 3 / 2 O2 E 0 = 1.172 V relative to SHE

[0152] However, neither H2 nor H2O was used to generate protons in this study. Protons were most likely generated by the oxidation of EtOH or THF at the anode. Since the equilibrium potential for the oxidation of EtOH to CO2 is approximately 0.10 V relative to the SHE, and the equilibrium potential for the oxidation of THF to THF-OH is 0.85 V relative to the SHE, the equilibrium potential for NH3 synthesis as a proton source is 0.043 V relative to the SHE, and for the THF source, it is approximately 0.8 V relative to the SHE. Ideally, protons should originate from water splitting, resulting in the highest voltage efficiency among all proton sources. Figure 6 shows the experimentally measured Faraday efficiency, the voltage efficiency obtained using 1.172 V relative to the SHE (i.e., water as the proton source), and the energy efficiency for different operating conditions. The energy efficiency did not vary significantly because most experiments were conducted at a fixed operating current density, thus the total cell potential remained almost constant across all study conditions. The highest observed energy efficiency was approximately 9%. The lower energy efficiency is primarily due to the lower voltage efficiency. This is because the electrochemical cell used in this study is a vial in which the electrodes are immersed in the electrolyte, which has excessive ohmic losses. Detailed instructions for energy efficiency calculations are provided in the Methods section.

[0153] Voltage efficiency primarily determines the energy efficiency of LiMAS. Voltage efficiency depends to a large extent on the proton source, such as H2O, H2, alcohols, or other hydrogen supports. Figure 7 The voltage efficiency versus cell potential for various proton sources is shown. It can be observed that the highest efficiency is achieved when the proton source is H₂O. However, utilizing H₂O in LiMAS is challenging. The voltage efficiency decreases in the following order of proton sources: H₂O >> H₂ > alcohol. Furthermore, to prevent Li metal oxidation, the operating potential must be lower than that of Li in THF. + The equilibrium potential of / Li is -2.98 V relative to SHE. 20 Therefore, the minimum pool potential for H2O oxidation at the anode and Li deposition at the cathode is 1.23 V - (−2.98 V) = 4.21 V. This limits the energy efficiency of LiMAS to 27.83%.

[0154] Technical-economic analysis

[0155] Previously reported 21 A preliminary techno-economic model of LiMAS was developed for green NH3 production, linearly scaling up to an industrial level of 1,000,000 tons per year, assuming no economies of scale. 4 mA / cm 2 The report states that it is $384 per ton. 21The estimated CapEx is linearly proportional to the NH3 current density. Since the operating pressure in this study (approximately 20 bar) is higher than that used in previous techno-economic analyses, we also considered the additional CapEx cost associated with the autoclave-based electrochemical cell for continuous operation. We assumed a single autoclave unit to be 500 cells with 0.2 m diameters connected to a single high-voltage line. 2 A stack of 40 electrodes in an electrochemical cell. The additional CapEx cost associated with one autoclave is $100,000. The number of autoclave units required is linearly proportional to the current density. Figure 8A shows that the CapEx cost decreases sharply with increasing current density. At 100 mA / cm² 2 At the optimal NH3 current density, the estimated CapEx is $84 per ton of NH3, which is lower than the environmental LiMAS method ($384 per ton). 21 It is 78% lower and 84% lower than the improved green Haber-Bosch process ($522 per tonne).

[0156] OpEx costs include the cost of electricity to operate the autoclave and the cost of utilities to operate the auxiliary equipment. Electricity costs are assumed to be $10 / MW-hr, while the utilities required for auxiliary equipment are fixed at $88 per tonne of NH3. 21 OpEx cost increases linearly with cell voltage, such as Figure 8B As shown. Figure 7 As shown, LiMAS requires a minimum of 4.21 V with H2O as the proton source and a minimum of 2.98 V with H2. This results in a minimum OpEx cost of $287 per tonne with H2O as the proton source and a minimum OpEx cost of $229 per tonne with H2. Considering the overpotential losses required at the anode and cathode, a cell voltage of 6 V is a reasonable operating potential for practical purposes. At an operating potential of 6 V, the OpEx cost is $372 per tonne, with an energy efficiency of approximately 20%. The OpEx cost of this program is 53% lower than that of environmentally stressed LiMAS ($790 per tonne) and 18% lower than that of the improved green Haber-Bosch process ($454 per tonne).

[0157] LiMAS plant at 100 mA / cm 2Operating at a low NH3 current density and a 6V cell voltage will result in a green NH3 cost of $456 per tonne, which would reduce the cost of NH3 by >61% compared to environmental LiMAS and by >53% compared to a similarly scaled improved green Haber-Bosch system. The significant reduction in capital and operating expenditures underscores the economic viability of large-scale high-pressure LiMAS. The findings point to the potential for a profound transformation in the ammonia production industry, guaranteeing both environmental benefits and significant economic advantages. We anticipate a market price of less than $400 / tonne for green NH3 production based on this method, including a discounted payback period of less than four years. The future target price for this technology is less than $100 / tonne.

[0158] in conclusion

[0159] Li-mediated ammonia synthesis (LiMAS) is a promising method for the electrochemical synthesis of NH3. The NH3 synthesis scheme in LiMAS involves three important steps: Li... + Electrodeposition, Li nitriding, and Li3N proton decomposition. + Electrodeposition, and secondly, the stability of the solid-electrolyte interface (SEI), are the most important aspects of ensuring stable operation and cell voltage in LiMAS. The LiMAS reactor was operated with a square-wave current profile, in which a working current density was applied for 2 minutes, followed by a 2-minute rest period at open-circuit voltage. The square-wave current profile helps improve SEI and voltage stability. The square-wave current profile also balances the reaction time of Li nitridation during the working time and the reaction time of Li3N proton decomposition during the rest period, which also controls the coverage of Li3N.

[0160] Side reactions involving Li proton decomposition also lead to the inhibition of H2 formation in Li nitridation. Since both rate-limiting steps – Li proton decomposition of H2 and Li3N proton decomposition of NH3 – are thermochemical, NH3 FE does not change with increasing cell voltage or applied current density. However, the availability of N2 and protons directly affects Li nitridation and Li3N proton decomposition, thus influencing NH3 selectivity. NH3 FE increases and reaches a maximum of approximately 35% when the pressure increases up to a maximum of 20 bar. Above 20 bar, N2 pressure has no effect on NH3 FE, suggesting that Li3N proton decomposition may be mass-transfer limited by proton donors. Increasing the proton donor concentration reduces the mass transfer limitation and shows an improvement in NH3 FE. However, after a certain concentration limit, further increases in proton donor concentration decrease NH3 FE, likely due to the increased rate of Li proton decomposition. Similar behavior was observed at all three pressures studied (20 bar, 50 bar, and 100 bar), and higher ethanol concentrations did not improve performance at higher pressures. The pKa of the proton donor can also affect proton availability. From methanol to 1-butanol, the pKa increases with increasing alkyl chain length of the proton donor, then decreases for 1-pentanol. NH3 FE also follows the same trend, with 1-butanol producing the largest FE. The decreasing diffusion coefficient with increasing alkyl chain length can also have some effect on proton donor mass transfer and NH3 FE.

[0161] The anions of Li salts can also affect the stability of SEI and NH3 FE. Increasing the anion size reduces the Li at the cathode. + Gradient and electric field, previously reported to favor dendrite-free deposition of Li metal, were used with larger BF4. - Anions replace ClO4 - Anions improved the performance of LiMAS. When using 0.065 ethanol concentration, 20 bar N2 pressure, and 3 M LiBF4, the performance was improved at −150 mA / cm². 2 At the applied current density, approximately 70% of the maximum NH3 FE and approximately −100 mA / cm were observed. 2 The maximum NH3 current density. The role of SEI in understanding NH3 FE is not well understood in the literature and requires in-situ studies, such as ambient pressure XPS and neutron reflectivity studies to investigate SEI in situ, and possibly under operating conditions.

[0162] The proton source in LiMAS plays a crucial role in achieving higher energy efficiency. The requirement to maintain the cathode potential at the Li plating equilibrium potential (i.e., −2.98 V relative to SHE) limits the achievable energy efficiency. Energy efficiency decreases in the order of H₂O >> H₂ > alcohol. The highest achievable energy efficiency using H₂O as the proton source is 27.83%, but implementing such a LiMAS system is extremely difficult. Preliminary techno-economic analysis shows that high-pressure LiMAS is significantly superior to ambient LiMAS and the improved Haber-Bosch process. LiMAS plants at 100 mA / cm²... 2 Operating at an NH3 current density and a cell voltage of 6V will produce green NH3 at an all-inclusive cost of $456 per tonne, which will reduce the cost of NH3 by >61% compared to environmental LiMAS and by >53% compared to a similarly sized improved green Haber-Bosch system. The significant reduction in capital and operating expenditures underscores the economic viability of large-scale high-voltage LiMAS.

[0163] References for Example 1

[0164] (1) Erisman, JW; Sutton, MA; Galloway, J.; Klimont, Z.;Winiwarter, W. How a century of ammonia synthesis changed the world. Naturegeoscience 2008, 1 (10), 636–639.

[0165] (2) Wang, L.;

[0166] (3) Andersen, S. Z.; Statt, M. J.; Bukas, V. J.; Shapel, S. G.;Pedersen, J. B.; Krempl, K.; Saccoccio, M.; Chakraborty, D.; Kibsgaard, J.;Vesborg, P. C. Increasing stability, efficiency, and fundamentalunderstanding of lithium-mediated electrochemical nitrogen reduction. Energy& Environmental Science 2020, 13 (11), 4291-4300。

[0167] (4) Lazouski, N.; Schiffer, Z. J.; Williams, K.; Manthiram, K.Understanding continuous lithium-mediated electrochemical nitrogen reduction.Joule 2019, 3 (4), 1127-1139。

[0168] (5) Fichter, F.; Girard, P.; Erlenmeyer, H. Elektrolytische Bindungvon komprimiertem Stickstoff bei gewöhnlicher Temperatur. Helvetica ChimicaActa 1930, 13 (6), 1228-1236。

[0169] (6) Tsuneto, A.; Kudo, A.; Sakata, T. Lithium-mediatedelectrochemical reduction of high pressure N2 to NH3. Journal ofElectroanalytical Chemistry 1994, 367 (1-2), 183-188。

[0170] (7) Lazouski, N.; Chung, M.; Williams, K.; Gala, M. L.; Manthiram, K.Non-aqueous gas diffusion electrodes for rapid ammonia synthesis fromnitrogen and water-splitting-derived hydrogen. Nature Catalysis 2020, 3 (5),463-469。

[0171] (8) Lazouski, N.; Steinberg, K. J.; Gala, M. L.; Krishnamurthy, D.;Viswanathan, V.; Manthiram, K. Proton donors induce a differential transporteffect for selectivity toward ammonia in lithium-mediated nitrogen reduction.ACS Catalysis 2022, 12 (9), 5197-5208。

[0172] (9) Cherepanov, P. V.; Krebsz, M.; Hodgetts, R. Y.; Simonov, A. N.;MacFarlane, D. R. Understanding the factors determining the faradaicefficiency and rate of the lithium redox-mediated N2 reduction to ammonia.The Journal of Physical Chemistry C 2021, 125 (21), 11402-11410。

[0173] (10) Rakov, D.; Hasanpoor, M.; Baskin, A.; Lawson, J. W.; Chen, F.;Cherepanov, P. V.; Simonov, A. N.; Howlett, P. C.; Forsyth, M. Stable andEfficient Lithium Metal Anode Cycling through Understanding the Effects ofElectrolyte Composition and Electrode Preconditioning. Chemistry of Materials2021, 34 (1), 165-177。

[0174] (11) Suryanto, B. H.; Matuszek, K.; Choi, J.; Hodgetts, R. Y.; Du,H.-L.; Bakker, J. M.; Kang, C. S.; Cherepanov, P. V.; Simonov, A. N.;MacFarlane, D. R. Nitrogen reduction to ammonia at high efficiency and ratesbased on a phosphonium proton shuttle. Science 2021, 372 (6547), 1187-1191。

[0175] (12) Du, H.-L.; Chatti, M.; Hodgetts, R. Y.; Cherepanov, P. V.;Nguyen, C. K.; Matuszek, K.; MacFarlane, D. R.; Simonov, A. N.Electroreduction of nitrogen with almost 100% current-to-ammonia efficiency.Nature 2022, 609 (7928), 722-727。

[0176] (13) Sažinas, R.; Andersen, S. Z.; Li, K.; Saccoccio, M.; Krempl, K.;Pedersen, J. B.; Kibsgaard, J.; Vesborg, P. C. K.; Chakraborty, D.;Chorkendorff, I. Towards understanding of electrolyte degradation in lithium-mediated non-aqueous electrochemical ammonia synthesis with gaschromatography-mass spectrometry. RSC advances 2021, 11 (50), 31487-31498。

[0177] (14) Sažinas, R.; Li, K.; Andersen, S. Z.; Saccoccio, M.; Li, S.;Pedersen, J. B.; Kibsgaard, J.; Vesborg, P. C.; Chakraborty, D.;Chorkendorff, I. Oxygen-Enhanced Chemical Stability of Lithium-MediatedElectrochemical Ammonia Synthesis. The Journal of Physical Chemistry Letters2022, 13 (20), 4605-4611。

[0178] (15) Li, K.; Andersen, S. Z.; Statt, M. J.; Saccoccio, M.; Bukas, V.J.; Krempl, K.; Sažinas, R.; Pedersen, J. B.; Shadravan, V.; Zhou, Y.Enhancement of lithium-mediated ammonia synthesis by addition of oxygen.Science 2021, 374 (6575), 1593-1597。

[0179] (16) Li, K.; Shapel, S. G.; Hochfilzer, D.; Pedersen, J. B.; Krempl,K.; Andersen, S. Z.; Sažinas, R.; Saccoccio, M.; Li, S.; Chakraborty, D.Increasing Current Density of Li-Mediated Ammonia Synthesis with High SurfaceArea Copper Electrodes. ACS Energy Letters 2021, 7 (1), 36-41。

[0180] (17) Li, S.; Zhou, Y.; Li, K.; Saccoccio, M.; Sažinas, R.; Andersen,S. Z.; Pedersen, J. B.; Fu, X.; Shadravan, V.; Chakraborty, D.Electrosynthesis of ammonia with high selectivity and high rates viaengineering of the solid-electrolyte interphase. Joule 2022, 6 (9), 2083-2101。

[0181] (18) Fu, X.; Pedersen, J. B.; Zhou, Y.; Saccoccio, M.; Li, S.; Sažinas, R.; Li, K.; Andersen, S. Z.; Xu, A.; Deissler, N. H. Continuous-flowelectrosynthesis of ammonia by nitrogen reduction and hydrogen oxidation.Science 2023, 379 (6633), 707-712。

[0182] (19) Xu, X.; Liu, Y.; Hwang, J. Y.; Kapitanova, O. O.; Song, Z.; Sun,Y. K.; Matic, A.; Xiong, S. Role of Li‐Ion depletion on electrode surface:underlying mechanism for electrodeposition behavior of lithium metal anode.Advanced Energy Materials 2020, 10 (44), 2002390。

[0183] (20) Westhead, O.; Tort, R.; Spry, M.; Rietbrock, J.; Jervis, R.;Grimaud, A.; Bagger, A.; Stephens, I. L. The origin of overpotential inlithium-mediated nitrogen reduction. Faraday Discussions 2023。

[0184] (21) Gomez, J. R.; Garzon, F. Preliminary economics for green ammoniasynthesis via lithium mediated pathway. International Journal of EnergyResearch 2021, 45 (9), 13461-13470。

[0185] (22) Andersen, S. Z.; Čolić, V.; Yang, S.; Schwalbe, J. A.;Nielander, A. C.; McEnaney, J. M.; Enemark-Rasmussen, K.; Baker, J. G.;Singh, A. R.; Rohr, B. A. A rigorous electrochemical ammonia synthesisprotocol with quantitative isotope measurements. Nature 2019, 570 (7762),504-508。

[0186] Example 2 – Calcium System

[0187] Materials and Methods

[0188] Electrochemical Experiment

[0189] The electrochemical synthesis of ammonia was carried out using a specialized 2-electrode apparatus comprising a single-chamber glass tank housed within a custom-designed autoclave encased in an explosion-proof enclosure. The salts used in the calcium-mediated reaction were dried in a vacuum oven for 24 hours to remove any moisture. The sealed Ca salt was opened in a glove box and used to prepare the electrolyte under an argon atmosphere. An oxygen sensor (ATO-GD200-O2) was placed inside the glove box to monitor oxygen levels. The electrolyte used was a 0.5 M solution of dry calcium perchlorate tetrahydrate dissolved in dimethoxyethane (DME), with the addition of 0.065 M ethanol (EtOH) and pre-saturation with nitrogen (N2) at a flow rate of 200 standard cubic centimeters per minute (sccm) for 10 minutes. Nickel (Ni) foam was used as the cathode, with fresh Ni foam used for each run. Prior to the reaction, the Ni foam was washed with ethanol to remove water contamination and then dried in an oven at 80°C for 20 minutes. A planar platinum (Pt) anode was used, cleaned by sonication in acetone and ethanol after each reaction, followed by drying in an oven at 80°C for 20 minutes. The Ni foam and Pt anode were electrically connected using copper (Cu) wires and Cu strips. The glass tank and magnetic stir bar were dried at 80°C for 1 hour before assembly. The distance between the anode and cathode was approximately 1 cm, and the cathode surface area facing the anode was 4 cm². Before the electrochemical experiments, the autoclave was purged 10 times with N₂ from a gas cylinder to remove oxygen and other contaminants, and then pressurized to the desired pressure of 6 bar. All gases were purged through a purifier (Vici metronics - P300-1) at the main pipeline before supply. Electrochemical experiments were conducted using a potentiostat (Biologic SP 300) with stirring at 700 rpm. Chorometric potentiometry was performed for 2 hours using different current densities ranging from −5 mA / cm² to −50 mA / cm². All measurements were performed at room temperature.

[0190] NMR

[0191] For NMR analysis using a QCI-F cryoprobe on a Bruker Neo 600 MHz system, dimethyl sulfoxide-d6 (DMSO-d6) was used as the deuterated solvent. To prepare the sample, 1 mL of post-electrolyte was mixed with 1 mL of 0.1 M H₂SO₄ to convert all NH₃ to ammonium sulfate. The mixture was thoroughly mixed, and then the solvent was evaporated using a rotary evaporator (Acrossinternational 2L). When the remaining solvent was reduced to 1 / 5 of its original volume, water was added to restore it to its original volume. The resulting solution was thoroughly mixed and centrifuged. Subsequently, 570 μL of the solution was added together with 30 μL of DMSO-d6 to an NMR tube for further analysis. NH₄Cl and 15 Calibration solutions of NH4Cl were prepared from 2 mM to 10 mM in the same manner. The resulting solutions were then transferred to NMR tubes for testing. Measurements were performed using a Bruker spectrometer equipped with a cryopreservation probe. The data presented in this paper represent the cumulative total of 16 scans. To suppress water resonance, excitation shaping with a 3-ms 180° shaping pulse centered at 4.612 ppm was employed. A perfect echo variant was selected to minimize J-modulation of the sample analyzed at 500 MHz. A total of 1,024 transient scans were recorded with a 1-second inter-scan delay. Each free-induction decay was acquired with 64,000 complex points and an acquisition time of 3.4 seconds. The processed spectra were zero-filled to 64,000 real points and an exponential apodization function with a line broadening factor (lb) of 0.3 Hz was applied before Fourier transform.

[0192] SEM

[0193] SEM was performed on a Hitachi SU8030 scanning electron microscope. Samples were coated with 20 nm gold. The accelerating voltage for EDS analysis was set to 30 kV, and the probe current was set to 75 mA.

[0194] XPS

[0195] XPS was performed on a ThermoFisher NEXSA-G2 to analyze the surface of deposits on Ni electrodes. The X-ray source was a monochromatic Al K-α. Full-spectrum scans were performed at a resolution of 1 eV between 0 eV and 1000 eV. The full-spectrum scans were averaged across three scans to minimize noise. Following the full-spectrum scans, elemental scans were performed at a resolution of 0.1 eV between 340 eV and 360 eV to identify the Ca 2p¹ / ² and 2p³ / ² peaks. To minimize noise, high-resolution elemental scans of Ca were averaged across ten scans.

[0196] XPS confirmed the presence of Ca on the Ni substrate. 0and Ca +2 Material. Since XPS is a surface analysis technique, negligible signals from Ni are obtained because the electron beam is focused on the deposited material.

[0197] Results and discussion

[0198] This study investigated calcium as a candidate material for N2 activation and electrochemical NH3 synthesis. Ca was chosen for detailed analysis because it was expected to be the most reactive, and its standard reduction potential (−2.87 V vs. SHE) is close to that of Li (−3.04 V vs. SHE), suggesting the potential success of similar experimental protocols. The formation of Ca3N2 is favorable due to the spontaneous reaction of N2 and Ca, as the free energy for Ca3N2 formation is −4 eV. The formation of bulk nitrides is known to be kinetically slow. 35、36 However, as discussed above, we assume that bulk nitride formation is not necessary for the successful mediation of this process. We assume that Ca-mediated NH3 synthesis occurs in a process similar to Li-mediated NH3 synthesis, i.e., based on the following reaction scheme and also as shown in Scheme 1:

[0199] [Ca electrodeposition] (i)

[0200] [Ca nitridation] (ii)

[0201] [Proton decomposition of Ca3N2] (iii)

[0202] [Ca3N2H proton decomposition] + X - (iv)

[0203] [Proton decomposition of Ca3N2H2] + X - (v)

[0204] [NH3 desorption] (vi)

[0205] [Ca3N nitriding] (vii)

[0206] First, Ca is electrodeposited onto the substrate by dissolving the Ca salt in a non-aqueous solvent (calcium electrodeposition, equation (i)) and applying a strong reducing bias at the cathode. The electrodeposited Ca metal spontaneously reacts with N2 (dissolved or gaseous in the GDE device) to form Ca3N2 (calcium nitride, equation (ii)). Following the formation of Ca3N2, a series of proton-coupled electron transfer steps (equations (iii) to (v)) form NH3 adsorbed onto the calcium nitride (calcium nitride proton decomposition). Finally, NH3 desorbs, forming surface N vacancies on the calcium nitride (equation (vi)). Given the stability of these surface nitride vacancies, we hypothesize that they are filled with N2 and subsequently reduced via a series of CPET reactions, thus completing the catalytic cycle. The Ca metal and nitride can also act as catalysts for hydrogen evolution to form H2 (an undesirable side reaction) (calcium proton decomposition). We again note that this proposed mechanism differs slightly from those presented in some published reports on similar Li-mediated NH3 synthesis methods. 13、15 It has been assumed that the accompanying dissolution of Li involves the formation of Li. + As discussed above, the precise mechanisms remain poorly understood and likely depend heavily on the specific details of the experimental protocol used (e.g., dynamic potential control, choice of electrolytes and salts, N2 pressure, etc.). However, here we assume that concomitant dissolution cannot occur under the commonly used strong reducing conditions, as the erosion reaction would be endothermic. In this document, we provide a conceptual proof of Ca and Mg-mediated NH3 synthesis.

[0207] In the lithium system of Example 1, we observed that increased N2 pressure led to improved NH3 Faraday efficiency (FE). This improvement only extended to a certain level, beyond which NH3 FE did not improve because the system was no longer under N2 mass transfer limitation. 10Similarly, there exists an optimal concentration of proton donor for balancing the Li3N proton decomposition (to NH3) and Li proton decomposition (to HER) steps. Therefore, for Ca-mediated NH3 synthesis, we decided to operate the reactor at a slightly elevated N2 pressure of 6 bar. Ethanol (EtOH, also known as HX in equations (iii), (iv), and (v)) was used as the proton donor at a concentration of 0.65 M. The reaction was carried out in a modified autoclave apparatus to withstand high pressure, as shown in Figure 9A. In the membrane-free apparatus, Ni foam was used as the cathode and Pt as the anode, and the electrolyte was stirred at 700 rpm. Tetrahydrofuran (THF) is typically used as an aprotic solvent to dissolve the Li salt in Li-mediated NH3 synthesis. One of the challenges of Ca-mediated NH3 synthesis is having a suitable Ca salt that can dissolve in an aprotic solvent. Calcium salts generally have poor solubility in water and most are insoluble in non-aqueous solvents. Water-soluble Ca salts are usually present in their hydrated form because they are hygroscopic. Of the Ca salts tested, Ca(ClO4)2 exhibited good solubility in dimethoxyethane (DME). The water content in the freshly prepared preelectrolytes was measured using a Karl Fischer titrator, yielding an average of 3.04% ± 0.12%. Experiments were conducted at different current densities ranging from 5 mA / cm² to 45 mA / cm², as illustrated in Figure 9B. At lower current densities, the calcium deposition rate was lower, resulting in fewer Ca sites available for the nitriding step and less formation of nitrides on the calcium surface. With increasing current density and therefore cell potential, the selectivity of calcium nitridation proton decomposition relative to calcium proton decomposition appeared to improve, as illustrated by the increased FE of NH3 in Figure 9B. At −15 mA / cm², the selectivity was higher. 2 At this current density, the calcium nitride and calcium nitride proton decomposition steps appear to reach an optimal equilibrium, producing a maximum of 50% NH3 FE. At higher current densities, such as −30 mA / cm², this is achieved. 2 and −45 mA / cm 2 At lower current densities, the cell voltage increases rapidly, which can lead to electrochemical degradation of the solvent and undesirable SEI formation. Therefore, we observed low NH3 FE at higher current densities. Stable performance requires an optimal cell voltage of approximately 4 V.

[0208] use 1 Quantitative analysis of ammonia was performed using 1H NMR spectroscopy, following a previously published protocol that ensures the measured NH3 originates from electrochemical N2 reduction rather than from air or other potential sources of pollution. 9 This method involves using 15 N2 isotopes serve as the basis for electrochemical N2 reduction. Because... 15 Nitrogen isotopes are spin-half nuclei, therefore... 15 Ammonia generated by N2 electrolysis1 The 1H NMR spectrum will give a characteristic double peak at 7.52 ppm with a coupling constant of 180 Hz. This double peak can be easily correlated with the most abundant... 14 The ammonia-related triplet of the nitrogen isotope (spin-1 nucleus) (occurring at 6.89 ppm with a coupling constant of 54 Hz) distinguishes the samples. The resulting spectra of the electrolyte samples at different current densities are depicted in Figure 9C. The isotope labeling experiments were performed at −15 mA / cm², as this condition yielded the highest FE and ammonia current densities. The isotope labeling experiments used… 1 Quantization is performed using H-NMR, such as Figure 9D The figure depicts 50% ± 0.2% FE produced at −15 mA / cm². Rigorous control experiments were conducted to ensure that NH₃ was produced via the electrochemical reduction of N₂ and not by harmful pollutants. To depict the accumulation of ammonia over time, two different experiments were performed in a batch system. One experiment was run for 2 hours at −15 mA / cm², and the other for 1.5 hours. Isotope labeling experiments were performed using… 1 Quantization is performed using H-NMR, such as Figure 9D The figure depicts the production of 50% ± 0.2% FE at −15 mA / cm². In an isotope labeling experiment conducted at −15 mA / cm² for 1.5 hours, 38% NH₃ FE was obtained, along with an ammonia current density of 5.6 mA / cm². 14 N2 and 15 An open-circuit controlled experiment was conducted with both N2 and preelectrolyte, in which no potential was applied and the solution was kept on a stirred plate for 2 hours. NMR spectra of the preelectrolyte and postelectrolyte samples under both conditions showed no ammonia in the postelectrolyte sample. Additionally, an extra control experiment was conducted using argon (Ar) instead of N2 to pressurize the reactor. The reactor was pressurized to 6 bar with Ar, and the reaction was carried out at −15 mA / cm² for 2 hours. 1 Post-electrolyte analysis by 1H NMR showed no ammonia peak. Finally, an electrolyte sample was prepared and kept open in a fume hood to ensure that the ammonia was not from atmospheric pollutants but rather from electrochemical synthesis. After 2 hours in the fume hood... 1 1H NMR analysis showed no ammonia peak.

[0209] The post-electrolysis catalyst was characterized using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS). Figure 10A to Figure 10D The analysis was performed ex-situ solely to confirm Ca deposition. In-situ analysis to understand the interface would be of interest, but it is beyond the scope of this work.

[0210] Our 2nd floor kit

[0211] (1) MacFarlane, DR; Cherepanov , PV ; Choi , J. ; Suryanto , BH ;Hodgetts , RY ; Bakker , JM ; Vallana, FMF; Simonov, AN A roadmap to the ammonia economy. Joules 2020, 4(6), 1186-1205.

[0212] (2) Erisman, JW; Sutton, MA; Galloway , J. ; Klimont, Z.;Winiwarter, W. How a century of ammonia synthesis changed the world.Naturegeoscience 2008, 1(10), 636–6

[0213] (3) Christensen, CH; Johannessen , T. ; Sørensen, RZ; Nørskov, JK Towards an ammonia-mediated hydrogen economy? Catalysis Today 2006, 111(1-2), 140-144.

[0214] (4) Shipman, MA; Symes, MD Recent progress towards the electrosynthesis of ammonia from sustainable resources. Catalysis Today 2017,286, 57-68.

[0215] (5) Fu, X.; Zhang, J.; Kang, Y. Recent advances and challenges of electrochemical ammonia synthesis. Chem Catalysis 2022, 2022, 2(10), 2590–2613. DOI: https: / / doi.org / 10.1016 / j.checat.2022.09.001

[0216] (6) Qing, G.; Ghazfar, R.; Jackowski , ST ; Habibzadeh , F. ;Ashtiani , MM ; Chen , C.-P. ; Smith, MR, III; Hamann, TW RecentAdvances and Challenges of Electrocatalytic N2 Reduction to Ammonia. ChemicalReviews 2020, 120(12), 5437–5516. DOI: 10.1021 / acs.chemrev.9b00659.

[0217] (7) Du, H.-L.; Chatti, M.; Hodgetts , RY ; Cherepanov , PV ;Nguyen , CK ; Matuszek , K. ; MacFarlane , DR ; Simonov, ANElectroreduction of nitrogen with almost 100% current-to-ammonia efficiency.Nature 2022, 609(7928), 722-727.

[0218] (8) Choi, J.; Du, H.-L.; Nguyen, C. K.; Suryanto, B. H.; Simonov, A.N.; MacFarlane, D. R. Electroreduction of nitrates, nitrites, and gaseousnitrogen oxides: a potential source of ammonia in dinitrogen reductionstudies. ACS Energy Letters 2020, 5 (6), 2095-2097。

[0219] (9) Andersen, S. Z.; Čolić, V.; Yang, S.; Schwalbe, J. A.;Nielander, A. C.; McEnaney, J. M.; Enemark-Rasmussen, K.; Baker, J. G.;Singh, A. R.; Rohr, B. A. A rigorous electrochemical ammonia synthesisprotocol with quantitative isotope measurements. Nature 2019, 570 (7762),504-508。

[0220] (10) Andersen, S. Z.; Statt, M. J.; Bukas, V. J.; Shapel, S. G.;Pedersen, J. B.; Krempl, K.; Saccoccio, M.; Chakraborty, D.; Kibsgaard, J.;Vesborg, P. C. Increasing stability, efficiency, and fundamentalunderstanding of lithium-mediated electrochemical nitrogen reduction. Energy& Environmental Science 2020, 13 (11), 4291-4300。

[0221] (11) Kani, N. C.; Goyal, I.; Gauthier, J. A.; Shields, W.; Shields, M.; Singh, M. R. Pathway toward Scalable Energy-Efficient Li-Mediated Ammonia Synthesis. ACS Appl Mater Interfaces 2024, 16 (13), 16203-16212. DOI: 10.1021 / acsami.3c19499 From NLM.

[0222] (12) Sažinas, R.; Li, K.; Andersen, S. Z.; Saccoccio, M.; Li, S.; Pedersen, J. B.; Kibsgaard, J.; Vesborg, P. C.; Chakraborty, D.; Chorkendorff, I. Oxygen-Enhanced Chemical Stability of Lithium-Mediated Electrochemical Ammonia Synthesis. The Journal of Physical Chemistry Letters 2022, 13 (20), 4605-4611.

[0223] (13) Lazouski, N.; Schiffer, Z. J.; Williams, K.; Manthiram, K. Understanding continuous lithium-mediated electrochemical nitrogen reduction. Joule 2019, 3 (4), 1127-1139.

[0224] (14) Lazouski, N.; Steinberg, K. J.; Gala, M. L.; Krishnamurthy, D.;Viswanathan, V.; Manthiram, K. Proton donors induce a differential transporteffect for selectivity toward ammonia in lithium-mediated nitrogen reduction.ACS Catalysis 2022, 12 (9), 5197-5208。

[0225] (15) Lazouski, N.; Chung, M.; Williams, K.; Gala, M. L.; Manthiram,K. Non-aqueous gas diffusion electrodes for rapid ammonia synthesis fromnitrogen and water-splitting-derived hydrogen. Nature Catalysis 2020, 3 (5),463-469。

[0226] (16) Sažinas, R.; Andersen, S. Z.; Li, K.; Saccoccio, M.; Krempl, K.;Pedersen, J. B.; Kibsgaard, J.; Vesborg, P. C. K.; Chakraborty, D.;Chorkendorff, I. Towards understanding of electrolyte degradation in lithium-mediated non-aqueous electrochemical ammonia synthesis with gaschromatography-mass spectrometry. RSC advances 2021, 11 (50), 31487-31498。

[0227] (17) Li, K.; Shapel, S. G.; Hochfilzer, D.; Pedersen, J. B.; Krempl,K.; Andersen, S. Z.; Sažinas, R.; Saccoccio, M.; Li, S.; Chakraborty, D.Increasing Current Density of Li-Mediated Ammonia Synthesis with High SurfaceArea Copper Electrodes. ACS Energy Letters 2021, 7 (1), 36-41。

[0228] (18) Li, K.; Andersen, S. Z.; Statt, M. J.; Saccoccio, M.; Bukas, V.J.; Krempl, K.; Sažinas, R.; Pedersen, J. B.; Shadravan, V.; Zhou, Y.Enhancement of lithium-mediated ammonia synthesis by addition of oxygen.Science 2021, 374 (6575), 1593-1597。

[0229] (19) Li, S.; Zhou, Y.; Li, K.; Saccoccio, M.; Sažinas, R.; Andersen,S. Z.; Pedersen, J. B.; Fu, X.; Shadravan, V.; Chakraborty, D.Electrosynthesis of ammonia with high selectivity and high rates viaengineering of the solid-electrolyte interphase. Joule 2022, 6 (9), 2083-2101。

[0230] (20) Fu, X.; Pedersen, J. B.; Zhou, Y.; Saccoccio, M.; Li, S.; Sažinas, R.; Li, K.; Andersen, S. Z.; Xu, A.; Deissler, N. H. Continuous-flowelectrosynthesis of ammonia by nitrogen reduction and hydrogen oxidation.Science 2023, 379 (6633), 707-712。

[0231] (21) Cherepanov, P. V.; Krebsz, M.; Hodgetts, R. Y.; Simonov, A. N.;MacFarlane, D. R. Understanding the factors determining the faradaicefficiency and rate of the lithium redox-mediated N2 reduction to ammonia.The Journal of Physical Chemistry C 2021, 125 (21), 11402-11410。

[0232] (22) Rakov, D.; Hasanpoor, M.; Baskin, A.; Lawson, J. W.; Chen, F.;Cherepanov, P. V.; Simonov, A. N.; Howlett, P. C.; Forsyth, M. Stable andEfficient Lithium Metal Anode Cycling through Understanding the Effects ofElectrolyte Composition and Electrode Preconditioning. Chemistry of Materials2021, 34 (1), 165-177。

[0233] (23) Suryanto, B. H.; Matuszek, K.; Choi, J.; Hodgetts, R. Y.; Du, H.-L.; Bakker, J. M.; Kang, C. S.; Cherepanov, P. V.; Simonov, A. N.; MacFarlane, D. R. Nitrogen reduction to ammonia at high efficiency and rates based on a phosphonium proton shuttle. Science 2021, 372 (6547), 1187-1191。

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[0243] (33) Schwalbe, JA; Statt , MJ ; Chosy , C. ; Singh, AR; Rohr, BA; Nielander , AC ; Andersen, SZ; McEnaney , JM ; Baker , JG ;Jaramillo , TF ; Section A Combined Theory-Experiment Analysis of the SurfaceSpecies in Lithium-Mediated NH3 Electrosynthesis. ChemElectroChem 2020, 7(7), 1542-1549. DOI: https: / / doi.org / 10.1002 / celc.201902124 。 。

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[0246] (36) Ehrlich, P. Calcium, Strontium, Barium Nitride Ca3N2, Sr3N2, Ba3N2. In Handbook of Preparative Inorganic Chemistry 2nd Edition, Vol. 1; 1963; pp. 940-941。

[0247] Example 3 - Magnesium System

[0248] Materials and Methods

[0249] Electrochemical Experiments

[0250] The magnesium-mediated electrochemical synthesis of ammonia was carried out using a specialized 2-electrode apparatus comprising a single-chamber glass cell housed within a custom-designed autoclave enclosed in an explosion-proof enclosure. The electrolyte used was a solution of 1 M magnesium perchlorate dissolved in dimethylformamide (DMF), with the addition of 0.065 M ethanol (EtOH) and pre-saturation with nitrogen (N2) at a flow rate of 200 standard cubic centimeters per minute (sccm) for 10 minutes. Nickel (Ni) foam was used as the cathode, with fresh Ni foam used for each run. Prior to the reaction, the Ni foam was washed with ethanol to remove water contamination and then dried in an oven at 80°C for 20 minutes. A planar platinum (Pt) anode was used, cleaned after each reaction by ultrasonic treatment in acetone and ethanol, followed by drying in an oven at 80°C for 20 minutes. The Ni foam and Pt anode were electrically connected using copper (Cu) wires and Cu strips. The glass cell and magnetic stir bar were dried at 80°C for 1 hour prior to assembly. The distance between the anode and cathode was approximately 1 cm, and the cathode surface area facing the anode was 4 cm². Prior to the electrochemical experiments, the autoclave was purged 10 times with N₂ from a gas cylinder to remove oxygen and other contaminants, and then pressurized to the desired pressure of 6 bar. Electrochemical experiments were conducted using a potentiostat (Biologic SP 300) with stirring at 700 rpm. Chronopotentiometric measurements were performed according to the switching current strategy proposed by Anderson et al., with a current density of −5 mA / cm² for 2 minutes, followed by 0 mA / cm² for 2 minutes, depending on the need to change, stabilize, or adjust the working electrode potential. During the working cycle, current densities within the range of −5 mA / cm² were measured. 2 Up to −45 mA / cm 2 Various current densities were measured. All measurements were performed at room temperature.

[0251] Colorimetric quantification of products

[0252] NH3 was quantified using the indophenol blue method via a standard addition method to explain changes in the appearance and properties of the electrolyte solution following the electrochemical reaction. In this method, the post-electrolyte sample was diluted 100-400 times with 0.1 M H2SO4 to reach the detection limit. After dilution, any ammonia present would be in the form of ammonium ions. The solution was then centrifuged twice for 15 minutes each to obtain a clear solution. A calibration solution was prepared using 0.01 M NH4Cl as a stock solution and further diluted to prepare 100 µM-500 µM NH4Cl calibration solutions in H2SO4. A blank solution was prepared by adding 500 µL H2SO4, 500 µL phenol nitroprusside, and 500 µL alkaline sodium hypochlorite. Six sample vials were each containing 400 µL of centrifuged diluted electrolyte solution, 100 µL of internal standard aqueous solution (0.1 M H₂SO₄, 100 µM-500 µM NH₄Cl in 0.1 M H₂SO₄), 500 µL of phenol nitroprusside, followed by 500 µL of alkaline sodium hypochlorite. The mixtures were incubated in the dark at ambient temperature for 30 minutes. The color of the samples changed from colorless to blue. The absorbance of the samples was scanned as a function of wavelengths from 400 nm to 800 nm using a visible spectrometer (Genesys 30). The maximum absorbance was observed at 632 nm, and therefore 632 nm was chosen to measure the absorbance for quantification of NH₃. The absorbance of all six solutions at 632 nm was plotted linearly against concentration. The ratio of the intercept to the slope represents the molar amount of ammonia in the test sample. After calculating the molar amount, the concentration and partial current density were determined.

[0253] NMR

[0254] For NMR analysis using a QCI-F cryoprobe on a Bruker Neo 600 MHz system, dimethyl sulfoxide-d6 (DMSO-d6) was used as the deuterated solvent. To prepare the sample, 1 mL of post-electrolyte was mixed with 1 mL of 0.1 M H₂SO₄ to convert all NH₃ to ammonium sulfate. The mixture was thoroughly mixed, and the solvent was evaporated using a rotary evaporator. When the remaining solvent was reduced to 1 / 5 of its original volume, water was added to restore it to its original volume. The resulting solution was thoroughly mixed and centrifuged. Subsequently, 570 μL of the solution was added to an NMR tube along with 30 μL of 10 mM acetone prepared in DMSO-d6 for further analysis. The resulting solution was then transferred to an NMR tube for testing. Measurements were performed using a Bruker spectrometer equipped with a cryoprobe. The data presented in this paper represent the cumulative total of 16 scans. To suppress water resonance, an excitation shaping method using a 3-ms 180° shaping pulse centered at 4.612 ppm was employed. The perfect echo variant was selected to minimize J-modulation of the sample analyzed at 500 MHz. A total of 1,024 transient scans were recorded with a 1-second inter-scan delay. Each free-induction decay was acquired using 64,000 complex points and an acquisition time of 3.4 seconds. The processed spectrum was zero-filled to 64,000 real points and an exponential apodization function with a line broadening factor (lb) of 0.3 Hz was applied before Fourier transform. The NMR data were analyzed using MNova software. Signal-to-noise ratio was used to calibrate both the sample and product samples.

[0255] SEM

[0256] SEM was performed on a Hitachi SU8030 scanning electron microscope. The sample was coated with 20 nm platinum.

[0257] XPS

[0258] XPS was performed on a ThermoFisher NEXSA-G2 to analyze the surface of deposits on a Ni electrode. The X-ray source was a monochromatic Al K-α. Full-spectrum scans were performed at a resolution of 1 eV between 0 eV and 1000 eV. The full-spectrum scans were averaged across three scans to minimize noise. Following the full-spectrum scans, elemental scans were performed at a resolution of 0.1 eV between 55 eV and 47 eV to identify Mg 2p and 1311 eV, as well as the Mg 1s peak at 1296 eV. To minimize noise, high-resolution elemental scans of Mg were averaged across ten scans.

[0259] XPS confirmed the presence of Mg on the Ni substrate. Since XPS is a surface analysis technique, a negligible signal from Ni was obtained because the electron beam was focused on the deposited material. However, when the electron beam was focused on the bare Ni foam, a Ni peak was clearly observed.

[0260] The large amount of carbon observed in both cases indicates that the organic electrolyte decomposed and deposited on the Ni foam.

[0261] Results and discussion

[0262] Based on the results of Examples 1 and 2, magnesium was investigated, driven by even lower plating potentials (−2.37 V vs. SHE), making it a more efficient choice. We hypothesize that Mg-mediated NH3 synthesis occurs in a process similar to that of Li and Ca-mediated NH3 synthesis.

[0263] Consistent with the results in Examples 1 and 2, for the Mg-mediated NH3 synthesis, we chose to operate the reactor at a N2 pressure of 6 bar. Ethanol (EtOH) was designated as the proton donor at a concentration of 0.065 M. To accommodate the high pressure required for this process, we implemented a modified autoclave setup. In our experimental framework, Ni foam was used as the cathode, supplemented by Pt as the anode in a membrane-free configuration. Maintaining a stirring rate of 700 rpm ensured efficient mixing of the electrolyte throughout the reaction. However, we encountered challenges with the solubility of magnesium salts in various solvents tested against LiMAS and CaMAS, which proved to be rather limited and difficult to determine. We found that magnesium perchlorate exhibited better solubility, particularly in DMF and propylene carbonate, which facilitated our experimental progress. The propylene carbonate system exhibited higher viscosity, leading to increased resistance and therefore reduced efficiency. Additionally, no ammonia was detected in the propylene carbonate system.

[0264] The electrolyte consists of 1M magnesium perchlorate dissolved in DMF and 0.065M EtOH. We implemented a current switching strategy with a 1-minute operating time and a 1-minute rest time to stabilize the solid electrolyte interface (SEI). The duration of the rest time varied and was adjusted as needed to maintain system stability, resulting in a variable total operating time for various current densities. The rest current density was maintained at 0 mA / cm² (i.e., open-circuit voltage) while different operating current densities were applied, such as... Figure 11A to Figure 11B As shown in the diagram, the switching time is crucial for stabilizing the cell voltage by limiting the growth of the solid electrolyte interface (SEI) and maintaining its stability. During the operating time, magnesium (Mg) deposition primarily occurs when a negative current density is applied. The rate-limiting steps in this stage include Mg nitridation, Mg3N proton decomposition, and Mg proton decomposition. 11Conversely, during the resting period, when the current density is zero, Mg deposition ceases, and the thermochemical nitriding and proton decomposition steps become dominant. The degree of Mg nitriding depends on the N2 pressure, while Mg3N proton decomposition and Mg proton decomposition are influenced by the concentration of the proton donor (ethanol (EtOH)). The passivation SEI requires time (approximately one hour under the reported conditions) to form and selectively allows Mg2+ ions, N2, H2, NH3, and H+ to pass through. 11 We infer that the SEI enhances cell voltage stability by hindering the reduction of DMF at the electrodes. Switching time also affects mass transfer. Experiments show that the open-circuit potential should remain close to approximately 0.5V during the resting time. Deviations favor H2 formation via Mg proton decomposition. Therefore, optimizing the resting time is crucial. Stirring speed also affects Mg3N and Mg proton decomposition and can vary depending on the size and type of stirrer used. 11 If the open-circuit potential deviates significantly from 0.5V, adjustments can be made to restore it. If the potential is below this value, reducing the rest time, operating time, and stirring speed can restore the potential to 0.5V. Conversely, if the potential rises above this threshold, increasing the rest time, decreasing the operating time, and increasing the stirring speed can restore the potential to 0.5V. Based on our observations, we found that a 1-minute operating time and a rest time of 1 to 5 minutes are the optimal times for stabilizing the SEI, depending on the total current density.

[0265] As the current density (CD) increases, the CD of NH3 rises, while the FE of NH3 remains constant at an average of approximately 27%, as shown in Figure 3. The loss of FE can be attributed to excessive Mg deposition, electrolyte decomposition, and corrosion. Figure 12A to Figure 12B The results show that the productivity of NH3 and H2 increases proportionally with increasing current density. This suggests that the ratio of Mg proton decomposition to Mg3N2 proton decomposition rates is potential-independent, or that both proton decomposition steps may be unimpeded at high potentials. Therefore, the potential-independent behavior is likely due to the fixed fractional coverage of Mg3N2 on the cathode, since proton decomposition is a thermochemical step. The coverage of Mg3N2 is balanced by the nitriding and proton decomposition reactions, which are directly related to N2 pressure and proton donor, respectively. Figure 13A to Figure 13BA comparison of the Faradaic efficiency (FE) and ammonia current density (CD) of LIMAS, CaMAS, and MgMAS (all tested in our laboratory) is presented. As expected, LIMAS exhibits excellent ammonia CD, thanks to optimized conditions and extensive research that thoroughly investigates all relevant parameters. CaMAS also shows significant potential for good ammonia selectivity, although further work is needed to improve both ammonia CD and FE. MgMAS, while promising, still requires in-depth investigation to achieve comparable FE and CD.

[0266] Open-circuit controlled experiments were conducted without applying a potential, and the solution was stirred for 2 hours at a pressure of 6 bar N2. NMR spectra of both the pre-electrolyte and post-electrolyte samples showed that the post-electrolyte sample did not contain ammonia. Figure 14B As shown in the diagram. Additionally, another control experiment was conducted using argon (Ar) instead of N2 to pressurize the reactor. The reactor was pressurized to 6 bar with Ar and maintained at −15 mA / cm². 2 The reaction was carried out for 4 hours. (Use...) 1 Post-electrolyte analysis by 1H NMR showed no ammonia peak, as shown in 14A. Finally, an electrolyte sample was prepared and kept open in a fume hood to ensure that the ammonia was not derived from atmospheric pollutants but from electrochemical synthesis. After 2 hours in the fume hood, 1 1H NMR analysis showed no ammonia peaks, as depicted in 14B.

[0267] use 1 Quantitative analysis of ammonia was performed using 1H NMR spectroscopy, following a previously published protocol that ensures the measured NH3 originates from electrochemical N2 reduction, rather than from air or other potential sources of pollution. 9 With the richest content 14 The ammonia-related triplet of the N2 isotope (spin-1 nucleus) appears at 6.83 ppm with a coupling constant of 96 Hz. Figure 15A to Figure 15B The images show: A) 1H-NMR spectra of experiments at different current densities; B) NMR calibration curves at different current density points. Spectra of the electrolyte samples obtained at different current densities are depicted in 15A. Rigorous control experiments were conducted to ensure that NH3 was produced by the electrochemical reduction of N2 and not by contaminants. UV-Vis spectroscopy was also used for quantification via the indophenol blue method. Both UV-Vis and NMR were benchmarked and produced consistent results. An additive method was used to accurately determine ammonia.

[0268] The post-reaction samples were characterized using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS) to characterize the catalyst after electrolysis, such as... Figure 16A to Figure 16DAs shown in the image. This in-situ analysis was performed to confirm the deposition of Mg.

[0269] References for Example 3

[0270] (1) Goyal, IK, Nishithan; Olusegun, Samuel; Chinnabattigalla, Sreenivasulu; Bhawnani, Rajan; Glusac, Ksenija; Singh, Aayush; Gauthier, Joseph;

[0271] (2) Iriawan, H.; Andersen, SZ; Zhang, X.; Comer, BM; Barrio,J.; Chen, P.; Medford, AJ; Stephens, IEL; Chorkendorff, I.; 10.1038 / s43586-021-00053-y.

[0272] (3) Smil, V. Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production; The MIT Press, 2000. DOI: 10.7551 / mitpress / 2767.001.0001.

[0273] (4) Chen, S.; Qi, G.; Yin, R.; Liu, Q.; Feng, L.; Feng, X.; Hu, G.;Luo, J.; Liu, X.; Liu, W. Electrocatalytic nitrate-to-ammonia conversion onCoO / CuO nanoarrays using Zn–nitrate batteries. Nanoscale 2023, 15 (48),19577-19585, 10.1039 / D3NR05254K. DOI: 10.1039 / D3NR05254K。

[0274] (5) Lu, G.; Gao, S.; Liu, Q.; Zhang, S.; Luo, J.; Liu, X. Design ofmaterial regulatory mechanism for electrocatalytic converting NO / NO3− to NH3progress. Natural Sciences 2023, 3 (3), e20220047. DOI: https: / / doi.org / 10.1002 / ntls.20220047。

[0275] (6) Yang, M.; Meng, G.; Li, H.; Wei, T.; Liu, Q.; He, J.; Feng, L.;Sun, X.; Liu, X. Bifunctional bimetallic oxide nanowires for high-efficiencyelectrosynthesis of 2,5-furandicarboxylic acid and ammonia. Journal ofColloid and Interface Science 2023, 652, 155-163. DOI: https: / / doi.org / 10.1016 / j.jcis.2023.08.079。

[0276] (7) Kani, N. C.; Nguyen, N. H. L.; Markel, K.; Bhawnani, R. R.; Shindel, B.; Sharma, K.; Kim, S.; Dravid, V. P.; Berry, V.; Gauthier, J. A.; et al. Electrochemical Reduction of Nitrates on CoO Nanoclusters-Functionalized Graphene with Highest Mass Activity and Nearly 100% Selectivity to Ammonia. Advanced Energy Materials 2023, 13 (17), 2204236. DOI: https: / / doi.org / 10.1002 / aenm.202204236。

[0277] (8) Kani, N. C.; Prajapati, A.; Singh, M. R. Sustainable Routes for Photo-Electrochemical Synthesis of Ammonia Using Various Nitrogen Precursors. ACS ES&T Engineering 2022, 2 (6), 1080-1087. DOI: 10.1021 / acsestengg.1c00484。

[0278] (9) Andersen, S. Z.; Čolić, V.; Yang, S.; Schwalbe, J. A.; Nielander, A. C.; McEnaney, J. M.; Enemark-Rasmussen, K.; Baker, J. G.; Singh, A. R.; Rohr, B. A.; et al. A rigorous electrochemical ammonia synthesis protocol with quantitative isotope measurements. Nature 2019, 570 (7762), 504-508. DOI: 10.1038 / s41586-019-1260-x from NLM。

[0279] (10) Du, H.-L.; Chatti, M.; Hodgetts, R. Y.; Cherepanov, P. V.; Nguyen, C. K.; Matuszek, K.; MacFarlane, D. R.; Simonov, A. N. Electroreduction of nitrogen with almost 100% current-to-ammonia efficiency. Nature 2022, 609 (7928), 722-727. DOI: 10.1038 / s41586-022-05108-y。

[0280] (11) Kani, N. C.; Goyal, I.; Gauthier, J. A.; Shields, W.; Shields, M.; Singh, M. R. Pathway toward Scalable Energy-Efficient Li-Mediated Ammonia Synthesis. ACS Appl Mater Interfaces 2024, 16 (13), 16203-16212. DOI: 10.1021 / acsami.3c19499 from NLM。

[0281] (12) Kim, K.; Lee, S. J.; Kim, D. Y.; Yoo, C. Y.; Choi, J. W.; Kim, J. N.; Woo, Y.; Yoon, H. C.; Han, J. I. Electrochemical Synthesis of Ammonia from Water and Nitrogen: A Lithium-Mediated Approach Using Lithium-Ion Conducting Glass Ceramics. ChemSusChem 2018, 11 (1), 120-124, Article. DOI: 10.1002 / cssc.201701975 Scopus。

[0282] (13) Lazouski, N.; Chung, M.; Williams, K.; Gala, M. L.; Manthiram,K. Non-aqueous gas diffusion electrodes for rapid ammonia synthesis fromnitrogen and water-splitting-derived hydrogen. Nature Catalysis 2020, 3 (5),463-469. DOI: 10.1038 / s41929-020-0455-8。

[0283] (14) Schwalbe, J. A.; Statt, M. J.; Chosy, C.; Singh, A. R.; Rohr, B.A.; Nielander, A. C.; Andersen, S. Z.; McEnaney, J. M.; Baker, J. G.;Jaramillo, T. F.; et al. A Combined Theory-Experiment Analysis of the SurfaceSpecies in Lithium-Mediated NH3 Electrosynthesis. ChemElectroChem 2020, 7(7), 1542-1549. DOI: https: / / doi.org / 10.1002 / celc.201902124。

[0284] (15) Tsuneto, A.; Kudo, A.; Sakata, T. Lithium-mediatedelectrochemical reduction of high pressure N2 to NH3. Journal ofElectroanalytical Chemistry 1994, 367 (1), 183-188. DOI: https: / / doi.org / 10.1016 / 0022-0728(93)03025-K。

[0285] (16) Krebsz, M.; Hodgetts, RY; Johnston, S.; Nguyen, CK; Hora, Y.; MacFarlane, DR; Simonov, AN Reduction of dinitrogen to ammoniumthrough a magnesium-based electrochemical process at close-to-ambienttemperature. Energy & Environmental Science 2024, 17 (13), 4481-4487,10.1039 / D4EE01090F. DOI: 10.1039 / D4EE01090F.

[0286] (17) Andersen, SZ; Statt, MJ; Bukas, VJ; Shapel, SG; Pedersen, JB; Krempl, K.; Saccoccio, M.; Chakraborty, D.; Kibsgaard, J.; Vesborg, PCK; et al. Increasing stability, efficiency, and fundamental understanding of lithium-mediated electrochemical nitrogen reduction. Energy& Environmental Science 2020, 13 (11), 4291-4300, 10.1039 / D0EE02246B. DOI: 10.1039 / D0EE02246B.

[0287] It should be emphasized that the above embodiments of this disclosure are merely possible examples of implementation methods described to clearly understand the principles of this disclosure. Many variations and modifications can be made to the above embodiments without substantially departing from the spirit and principles of this disclosure. All such modifications and variations are intended to be included within the scope of this disclosure and protected by the appended claims.

Claims

1. A method for generating ammonia, the method comprising introducing nitrogen gas at a pressure higher than ambient pressure into an electrochemical cell, wherein the electrochemical cell comprises... (a) Reaction chamber; (b) an anode and a cathode, wherein the anode and cathode are located within the reaction chamber; (c) A voltage source that connects the cathode to the anode; (d) An ion-conducting membrane, wherein the ion-conducting membrane is located between the cathode and the anode; as well as (e) an electrolyte composition comprising (i) an organic solvent, (ii) a proton donor, and (iii) a salt or any combination of lithium, calcium, magnesium, strontium, yttrium, scandium, and zirconium, wherein the electrolyte composition is located between the anode and the cathode. An electric current is applied to the electrochemical cell to convert nitrogen into ammonia.

2. The method according to claim 1, wherein the pressure of the nitrogen gas in the electrochemical cell is from 1 bar to 100 bar.

3. The method according to claim 1 or 2, wherein the salt of lithium, calcium, magnesium, strontium, yttrium, scandium or zirconium is tetrafluoroborate, hexafluorophosphate hexafluoroarsenate, perchlorate, trifluoromethanesulfonate, bis(oxalate)borate, difluorooxalateborate, trifluorosulfonylimide salt or halide salt.

4. The method according to any one of claims 1 to 3, wherein the concentration of the lithium, calcium, magnesium, strontium, yttrium, scandium or zirconium salt in the electrolyte composition is from about 0.5 M to about 4.0 M.

5. The method according to any one of claims 1 to 4, wherein the proton donor comprises an alcohol.

6. The method according to any one of claims 1 to 4, wherein the proton donor comprises an alkyl alcohol, an aryl alcohol, or a cycloalkyl alcohol.

7. The method according to any one of claims 1 to 4, wherein the proton donor comprises a C1 to a C7 alkyl alcohol.

8. The method according to any one of claims 1 to 4, wherein the proton donor comprises ethanol.

9. The method according to any one of claims 1 to 8, wherein the concentration of the proton donor in the electrolyte composition is from about 0.01 M to about 0.40 M.

10. The method according to any one of claims 1 to 9, wherein the organic solvent comprises an ether.

11. The method of claim 10, wherein the ether comprises dimethyl ether, diethyl ether, diethylene glycol dimethyl ether, or triethylene glycol dimethyl ether.

12. The method according to any one of claims 1 to 9, wherein the organic solvent comprises a fluorinated solvent.

13. The method of claim 12, wherein the fluorinated solvent comprises a perfluoroalkane or a fluorobenzene.

14. The method according to any one of claims 1 to 9, wherein the organic solvent comprises tetrahydrofuran, dimethyl sulfoxide, dimethoxyethane, N,N-dimethylformamide, or any combination thereof.

15. The method according to any one of claims 1 to 14, wherein the current density of the current applied to the electrochemical cell is about −200 mA / cm². 2 To approximately 2,500 mA / cm 2 .

16. The method of claim 1, wherein the electrolyte composition comprises a calcium salt and the proton donor comprises ethanol, and the pressure of nitrogen in the electrochemical cell is from 1 bar to 10 bar.

17. The method according to claim 16, wherein the calcium salt is calcium perchlorate.

18. The method according to claim 16 or 17, wherein the organic solvent comprises dimethoxymethane.

19. The method according to any one of claims 16 to 18, wherein the current density of the current applied to the electrochemical cell is about −5 mA / cm². 2 Approximately −45 mA / cm 2 .

20. The method of claim 1, wherein the electrolyte composition comprises a magnesium salt, the proton donor comprises ethanol, and the pressure of nitrogen in the electrochemical cell is from 1 bar to 10 bar.

21. The method of claim 20, wherein the magnesium salt is magnesium perchlorate.

22. The method according to claim 20 or 21, wherein the organic solvent comprises N,N-dimethylformamide.

23. The method according to any one of claims 20 to 22, wherein the current density of the current applied to the electrochemical cell is about −40 mA / cm². 2 Approximately −20 mA / cm 2 .

24. The method of claim 1, wherein the electrolyte composition comprises a lithium salt, the proton donor comprises ethanol, and the pressure of nitrogen in the electrochemical cell is from 1 bar to 100 bar.

25. The method of claim 24, wherein the lithium salt is lithium perchlorate.

26. The method according to claim 24 or 25, wherein the organic solvent comprises tetrahydrofuran.

27. The method according to any one of claims 24 to 26, wherein the current density of the current applied to the electrochemical cell is about −150 mA / cm². 2 Approximately 600 mA / cm 2 .

28. The method according to any one of claims 16 to 27, wherein the concentration of ethanol in the electrolyte composition is from about 0.03 M to about 0.08 M.

29. The method according to any one of claims 1 to 28, wherein the anode comprises nickel, platinum, tungsten, a metal alloy, a metal oxide, or graphite.

30. The method according to any one of claims 1 to 29, wherein the cathode comprises steel, nickel, copper, titanium, molybdenum or graphite.

31. The method according to any one of claims 1 to 30, wherein the ion-conducting film comprises glass or a polymer.

32. The method of claim 31, wherein the polymer comprises polyethylene or polypropylene.

33. The method according to any one of claims 1 to 32, wherein the temperature in the reaction chamber is about 25°C to about 30°C.

34. The method according to any one of claims 1 to 33, wherein (i) the current is applied for a first time period, (ii) the current is turned off for a second time period, and (iii) the current is applied for a third time period.

35. The method according to any one of claims 1 to 34, wherein the electrolyte composition is stirred in the electrochemical cell.

36. The method according to any one of claims 1 to 35, wherein the reaction chamber comprises stainless steel.

37. The method according to any one of claims 1 to 36, wherein the reaction chamber includes a first orifice for introducing the electrolyte composition into the reaction chamber and a second orifice for introducing nitrogen gas into the reaction chamber.

38. The method according to any one of claims 1 to 37, wherein the reaction chamber includes a pressure gauge for measuring the pressure within the reaction chamber.

39. The method according to any one of claims 1 to 38, wherein the ammonia is removed from the reaction chamber after ammonia is generated.

40. The method according to any one of claims 1 to 39, wherein after ammonia is generated, (i) the electrolyte composition containing ammonia is removed from the reaction chamber and (ii) ammonia is removed from the electrolyte composition.

41. The method of claim 40, wherein after ammonia removal, the electrolyte composition is regenerated and introduced into the reaction chamber.

42. The method according to any one of claims 1 to 41, wherein the method is carried out continuously to produce ammonia.

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