Systems and methods for the electrosynthesis of syngas from carbonate capture liquid

Abstract

Electrolyzers are provided that comprise: a cathode comprising a porous, carbon support composed of solid carbon having surfaces which define a plurality of pores distributed throughout the solid carbon, the porous, carbon support comprising a plurality of amine groups and a metal phthalocyanine catalyst distributed on surfaces of the porous, carbon support, the cathode in contact with a catholyte comprising carbonate ions; an anode in electrical communication with the cathode; a membrane between the cathode and the anode and configured to generate in situ CO2 in the catholyte; and an interposer layer between the cathode and the membrane. Methods for producing CO are also provided comprising generating the in situ CO2 in the catholyte of the electrolyzer and reducing the in situ CO2 to CO at the cathode.

Description

Atty. Dkt. No.00100-0387-PCT SYSTEMS AND METHODS FOR THE ELECTROSYNTHESIS OF SYNGAS FROM CARBONATE CAPTURE LIQUID CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to U.S. provisional patent application number 63 / 639,066 that was filed April 26, 2024, the entire contents of which are incorporated herein by reference. BACKGROUND

[0002] Direct-air capture (DAC) of CO2often uses alkali hydroxides as a sorbent material and relies on an energy-intensive thermal CaCO3 / Ca(OH)2 step to release CO2 and regenerate the alkali hydroxide. By contrast, reactive capture systems use alkali carbonate post-capture liquid as feedstock and convert the captured CO2 to value-added products while regenerating the capture liquid. Bipolar membrane (BPM) electrolyzers with Ag cathode catalysts have been used for carbonate reduction, but they provide a relatively low CO Faradaic efficiency (FE) of < 25%, cell voltages of > 3.7 V at 100 mA cm–2, and consequent energy efficiencies (EE) of 39% at 100 mA cm–2that decline to < 35% at 300 mA cm–2. (Li, Y. C. et al. ACS Energy Letters 4, 1427-1431 (2019).) SUMMARY

[0003] Provided are electrochemical reactive capture systems (i.e., electrolyzers) configured to generate CO2in situ (i.e., i-CO2) and to reduce the i-CO2to products using certain catalysts. The catalysts and related methods are also provided.

[0004] The present disclosure is illustrated by reference to an Example below that describes a study of the limitations of performance in existing electrochemical reactive capture systems in which it is found that the catalyst becomes starved of CO2 even at moderate current densities, leading to a rapid decline in faradaic efficiency (FE). It is further demonstrated that this problem may be addressed, at least in part, by tuning the catalyst support. Specifically, by judicious tuning of the porosity characteristics of the catalyst support, considering both the accessibility of the pores’ inner surfaces as well as their geometric area, enables excellent access by CO2generated in situ (i.e., i-CO2) at the bipolar membrane to catalytic sites. The Example further describes the development of a polydopamine-coated catalyst support which disperses the catalyst, prevents catalystAtty. Dkt. No.00100-0387-PCT aggregation, and produces a desired electron-deficient metal center for favorable i-CO2 binding and activation. Notably, when catalysts such as cobalt phthalocyanine (CoPc) were incorporated onto a catalyst support without the polydopamine coating, it was found that they aggregated under bias, leading to low FE. In a carbonate electrolyzer including a cobalt phthalocyanine catalyst on a polydopamine-coated catalyst support, a FE of 43% to CO was achieved at 200 mA cm–2and 3.0 V, with < 1% CO2in the outlet stream. This corresponds to a projected energy efficiency (EE) to 2:1 syngas of 50% at 200 mA cm–2(when H2 is added using an operably coupled water electrolyzer). This result is significantly superior as compared to the best known existing carbonate-to-syngas electrified reactive capture system having a projected EE at 200 mA cm–2of 39%. (Li, Y. C. et al. ACS Energy Letters 4, 1427- 1431 (2019).)

[0005] In one aspect, an electrolyzer is provided that comprises: a cathode comprising a porous, carbon support composed of solid carbon having surfaces which define a plurality of pores distributed throughout the solid carbon, the porous, carbon support comprising a plurality of amine groups and a metal phthalocyanine catalyst distributed on surfaces of the porous, carbon support, the cathode in contact with a catholyte comprising carbonate ions; an anode in electrical communication with the cathode; a membrane between the cathode and the anode and configured to generate in situ CO2 in the catholyte; and an interposer layer between the cathode and the membrane. In another aspect, methods for producing CO are also provided comprising generating the in situ CO2 in the catholyte of the electrolyzer and reducing the in situ CO2 to CO at the cathode.

[0006] Other principal features and advantages of the disclosure will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Illustrative embodiments of the disclosure will hereafter be described with reference to the accompanying drawings.

[0008] FIG.1A shows an integrated process of reactive CO2capture, which is by contrast to a sequential process of direct air capture followed by CO2 electrolysis (not shown). FIG. 1B shows a carbonate electrolyzer fed using 1.5 M K2CO3as catholyte. Carbonate passes through the hydrophilic carbon paper, the catalyst layer, and the hydrophilic interposer layerAtty. Dkt. No.00100-0387-PCT (thickness: 135 µm) via convection and diffusion. CO32–reacts with H+from the BPM to generate i-CO2. The i-CO2passes back from the membrane interface and goes through the interposer layer to the catalyst layer for electroreduction to CO. The three boxes below illustrate the transport of i-CO2to CoPc catalyst molecules dispersed on three different carbon supports, including a planar (P) carbon support, a nanoporous (NP) carbon support, and a hierarchically porous (HP) carbon support.

[0009] FIG.2A shows Faradaic efficiency to CO for a gas-CO2-fed electrolyzer as a function of CO2 partial pressure.1.5 M K2CO3 was used as catholyte and anolyte. FIG.2B shows Faradaic efficiency to CO for a liquid carbonate-fed electrolyzer using CoPc catalyst loaded on a variety of carbon supports. FIG.2C shows Cdl / BET ratio on uncoated and PDA- coated carbon supports. FIGS.2D-2E show in situ Raman spectra of CoPc / HP and CoPc / PDA-HP supported catalysts in 1.5 M K2CO3. The in situ analysis was performed in a flow cell with three compartments. CoPc / PDA-HP was coated on the carbon paper substrate as the cathode, and Pt / C as the anode. FIG.2F shows Co1+:(Co1++ Co2+) ratio (as a percentage) as a function of applied potential for CoPc catalysts loaded on a variety of carbon supports: HP, PDA-HP, and PDA-P.

[0010] FIG.3A shows a comparison of Faradaic efficiency to CO for different PDA- coated carbon supports (left) and between an uncoated and PDA coated HP carbon support.. Electrolysis was carried out in the current density range of 100-600 mA cm−2. FIG.3B shows cell voltage (left Y-axis) and energy efficiency (right Y-axis) for carbonate electrolysis (1.5 M K2CO3) using different cell configurations. The energy efficiency was calculated using experimental data for a system that employed an optimized BPM and a NiFeOx anode. FIG. 3C shows cell voltage (left Y-axis) and Faradaic efficiency to CO (right Y-axis) for 42 hours of electrolysis at 100 mA cm−2for the case of the CoPc / PDA-HP catalyst. The interposer layer was replaced after 20 hours and after 40 hours.

[0011] FIG.4 shows a schematic illustration of CoPc catalyst molecules dispersed on a PDA-coated hierarchical porous carbon support, achieving enhanced dispersion of the catalysts and tailored electronic properties of the Co centers of the CoPc catalyst molecules.

[0012] FIG.5A shows Faradaic efficiency to CO and H2 on CoPc / PDA-HP at various PDA treatment times (longer treatment times provide thicker PDA coatings). FIG.5B shows Faradaic efficiency to CO and H2 on CoPc / PDA-HP at various loadings.Atty. Dkt. No.00100-0387-PCT

[0013] FIG.6 shows the amount of CO (left Y-axis) and gas CO2 (g) (right Y-axis) as a function of the average pore diameter of the interposer layer. The interposer thickness was 135 µm, and the electrolysis was performed at 200 mA cm−2for 30 min.

[0014] FIG.7 shows the Faradaic efficiency to CO and H2 on CoPc / PDA-HP catalyst when no interposer layer is used (compare to FIG.3A). DETAILED DESCRIPTION

[0015] Electrolyzers are provided which are configured to generate i-CO2in an electrolyte contained within the electrolyzer and to reduce the i-CO2 to products using certain supported catalysts which are further described below. The electrolyzer comprises a cathode comprising the supported catalyst, an anode in electrical communication with the cathode, and a membrane between the cathode and the anode.

[0016] The supported catalyst comprises (or consists of) a porous, conductive support and a catalyst distributed thereon. The catalyst of the supported catalyst is one capable of catalyzing the electrochemical reduction of CO2to CO. Illustrative such catalysts include metal phthalocyanine catalysts, (e.g., cobalt phthalocyanine (CoPc)), metal atom catalysts (e.g., Ag), single metal atom catalysts (e.g., Ni single atom), etc.

[0017] The porous, conductive support of the supported catalyst is composed of a solid conductive material (e.g., carbon) having surfaces which define a plurality of pores distributed throughout the solid conductive material. The specific porous, conductive support being used is selected on the basis of its surface area and accessibility of this surface area by CO2molecules. The surface area is desirably quite high, e.g., at least 1000 m2 / g, at least 1200 m2 / g, at least 1400 m2 / g, or a range of between any of these values. As demonstrated in the Example, below, accessibility is related to pore size and distribution of pore sizes. In embodiments, the solid surfaces of the porous, conductive support define at least two populations of pores, each having a different size. A first population of pores may have a larger size, which may be in a range of from 10 nm to 50 nm, from 10 nm to 35 nm, or from 10 nm to 20 nm. Such pores may be referred to as mesopores. A second population of pores may have a smaller size, which may be less than 2 nm, less than 1 nm, or in a range of from 1 to 2 nm. Such pores may be referred to as micropores. In embodiments, the porous, conductive support has a greater number of larger pores (e.g., mesopores) as compared to smaller pores (e.g., micropores). The porous, conductive support may have a pore ratioAtty. Dkt. No.00100-0387-PCT (defined as the number of larger pores to smaller pores) of at least 7, at least 10, at least 13, at least 15, or a range of between any of these values. Surface area, pore size, pore distribution, and pore ratios may be measured using Brunauer-Emmett-Teller (BET) analysis as described in the Example, below. The pore sizes above may be diameters and they may be average values as determined by BET analysis. It is noted that the solid conductive material itself may be in the form of a plurality of particles, e.g., as in a powder and schematically illustrated in FIG.1B. However, the pores in this paragraph refer to those defined within such particles and are distinguished from any additional pores formed between neighboring individual particles.

[0018] Porous, conductive supports having at least two populations of differently sized pores (e.g., both mesopores and micropores) within the ranges of pore ratios described above may be referred to as hierarchically porous (HP) supports. A schematic of a hierarchically porous carbon support is shown in FIG.1C (left). Such a support is distinguished from other porous carbon supports, e.g., the nanoporous (NP) carbon support shown in FIG.1C (middle, only micropores) and the planar (P) carbon support shown in FIG.1C (right, no pores).

[0019] The porous, conductive support is functionalized to increase association between the material of the porous, conductive support and the selected catalyst (as compared to association between the catalyst and the porous, conductive support in its unfunctionalized state). This may refer to a physical and / or chemical association that increases dispersion of the catalyst on surfaces of the porous, conductive support (e.g., by increasing immobilization / decreasing aggregation of the catalyst). Techniques such as TEM, XPS, EDX, and FTIR as described in the Example below, may be used to confirm sufficient physical and / or chemical association between the catalyst and the porous, conductive support to increase catalyst dispersion. This may also refer to an electronic association that increases charge transfer between the catalyst and the porous, conductive support. Sufficient charge transfer enables modification of the electronic structure of the catalyst so as to increase the number of sites on the catalyst that are catalytically active and to lower the energy of intermediate states involved in the electrochemical conversion of CO2 to CO. Catalytically active sites may be metal centers having an appropriate oxidation state to catalyze the electrochemical reduction of CO2 bound thereto. Using CoPc as an example, the catalytically active sites are Co1+Pc versus Co2+Pc. The functionalization may increase the relative number of Co1+Pc versus Co2+Pc sites at a particular applied electric potential (see FIGS.2D- 2F and 4). Techniques such as Raman spectroscopy, EXAFS, and DFT calculations asAtty. Dkt. No.00100-0387-PCT described in the Example below, may be used to confirm sufficient electronic association between the catalyst and the porous, conductive support to increase charge transfer therebetween. This includes quantification of catalytically active sites and formation energies of intermediate states. More generally, for metal phthalocyanine catalysts, the catalytically active sites may be referred to as M(n-1)+Pc and the catalytically inactive sites may be referred to as M(n)+Pc. The functionalization may provide a percentage of M(n-1)+Pc as compared to both M(n-1)+Pc and M(n)+Pc sites that is at least 90% at an applied potential of -1.2 V versus reversible hydrogen electrode. This includes at least 95%, at least 98%, and a range of between any of these values.

[0020] The functionalization may be provided by amine groups distributed on surfaces of the porous, conductive support. The amine groups may be provided by a coating on surfaces of the porous, conductive substrate that comprises the amine groups. This coating may be a polymeric coating, e.g., a polydopamine (PDA) coating. Other coatings that may be used include a polyaniline coating. The amine groups refer to NR3 groups, wherein R is independent selected from hydrogen, alkyl groups, and aryl groups. The amine groups may be secondary and / or tertiary amine groups such as those present in polydopamine and polyaniline.

[0021] Other coatings that may be used include a polytetrafluoroethylene coating. Metal oxide materials, e.g., TiO2, CeO2, and ZrO2 may also be used as coatings.

[0022] Methods of coating porous, conductive supports, including hierarchically porous carbon, with a polydopamine coating are provided in the Example, below. Briefly, this involves exposing the selected porous, conductive support to a solution of dopamine hydrochloride for a period of time (coating time). The thickness of the polydopamine coating (which is proportional to the coating time) may be selected to achieve a desired result, e.g., maximize faradic efficiency (FE) to CO. Illustrative coating times include from 20 minutes to 45 minutes, from 25 minutes to 40 minutes, and from 25 minutes to 35 minutes. (See FIG. 5A.)

[0023] The Example further describes methods for forming the supported catalyst comprising the functionalized porous, conductive support (e.g., polydopamine-coated hierarchically porous carbon) and the catalyst (e.g., CoPc) distributed thereon. This may involve providing the supported catalyst as an ink by combining the functionalized porous, conductive support, the catalyst, and other components, e.g., an ionomer (e.g., Nafion) and aAtty. Dkt. No.00100-0387-PCT solvent (e.g, an alcohol). Parameters such relative amounts of the components in the ink may be adjusted to achieve a desired result, e.g., maximize faradic efficiency (FE) to CO. This includes the relative amount of the catalyst and the functionalized porous, conductive support. (See FIG.5B.) Illustrative weight% include from 20 weight% to 35 weight% and from 20 weight% to 30 weight% (of the catalyst as compared to the total weight of the catalyst and the functionalized porous, conductive support). The ink may be coated onto a substrate (e.g., hydrophilic carbon paper) to form the cathode of the electrolyzer at a surface coverage selected to achieve a desired result, e.g., maximize faradic efficiency (FE) to CO. The cathode is in contact with a catholyte comprising carbonate ions (CO32-). The catholyte may be an aqueous alkali metal carbonate (e.g., K2CO3) solution.

[0024] The membrane between the anode and the cathode of the electrolyzer is configured to generate the i-CO2 in the catholyte. This may be accomplished by the membrane being configured to dissociate water contained within the electrolyzer, thereby generating protons and hydroxide ions. The membrane may be a bipolar membrane. On the cathode side of the electrolyzer, the protons may combine with the carbonate ions to generate the i-CO2 in the catholyte. As described in the Example, below, the membrane may comprise a catalyst (e.g., TiO2) to facilitate water dissociation.

[0025] The anode of the electrolyzer may be configured to facilitate the formation of oxygen (O2) from hydroxide ions present in the anolyte (including those generated by the membrane). Various anodes (e.g., NiFeOx) and anolytes (e.g., alkali metal hydroxides such as KOH) capable of achieving oxygen evolution may be used.

[0026] The electrolyzer generally comprises an interposer layer between the cathode and the membrane, the interposer layer configured to suppress hydrogen evolution at the membrane and to facilitate transport of the i-CO2 to the cathode. (See FIG.7.) The thickness of the interposer layer and the average pore size therein may be selected to achieve a desired result, e.g., maximize faradic efficiency (FE) to CO. (See FIG.6.) This includes an interposer layer having a thickness in a range of from 120 to 140 ^m and an average pore size in a range from 5 to 15 ^m. Other components may be used as desired, e.g., flow field plates.

[0027] A portion of an illustrative electrolyzer is shown in FIG.1B. This electrolyzer may be used as the “liquid-fed carbonate electrolyzer” shown in FIG.1A. The electrolyzer comprises a cathode comprising any of the disclosed supported catalysts (e.g., CoPc / PDA- coated HP), the cathode in contact with an aqueous alkali metal carbonate solution as theAtty. Dkt. No.00100-0387-PCT catholyte (fed to the electrolyzer via a feed inlet). The carbonate ions in the catholyte react with the protons from the bipolar membrane to generate i-CO2in the catholyte. Generating a potential difference between the anode and the cathode induces reduction of the i-CO2 at the cathode as catalyzed by the CoPc catalyst thereon. The products of the CO2reduction reaction (e.g., CO) may be collected via an outlet. The electrolyzer, e.g., the electrolyzer of FIG.1A and FIG.1B may also provide H2, which together with the CO, provides syngas. However, an additional water electrolyzer operably connected to the electrolyzer of FIG.1A and FIG.1B may be used to provide H2. Thus, the disclosed electrolyzers may be a component of a larger reactive CO2 capture system.

[0028] Methods for producing CO from i-CO2 are also provided. Such a method comprises generating i-CO2in a catholyte comprising carbonate ions, the catholyte in contact with a cathode of an electrolyzer, the cathode comprising a supported catalyst; and reducing the i-CO2to CO at the cathode. The methods may be carried out using any of the disclosed electrolyzers and any of the disclosed supported catalysts (e.g., CoPc / PDA-coated HP). Also encompassed are the supported catalysts themselves. EXAMPLE

[0029] Additional information, including that referenced as “data not shown” may be found in U.S. provisional patent application number 63 / 639,066 that was filed April 26, 2024, the entire contents of which are incorporated herein by reference.

[0030] Introduction

[0031] CO2(g) capture from the atmosphere, followed by electrochemical conversion, enables one route to lowering the carbon-intensity of fuels and chemicals. Because CO2(g) is a weak acid and dilute in the atmosphere, strong aqueous alkali hydroxide solutions, such as KOH, are used in direct air capture (DAC). Releasing, from the captured state, a stream of concentrated CO2, thus regenerating hydroxide from alkaline carbonates, requires additional energy-intensive steps, these typically totaling 8-10 GJ / tonCO2. When, in the context of carbon capture and upgrade (CCU), carbon monoxide (CO) is then produced from the captured CO2, the DAC process contributes 13-16 GJ / tonCO (GJ / tonCO2* 44 g / mol CO2 / 28 g / mol CO). This is considerable when referenced to the ~10 GJ / ton lower heating value (LHV) of CO.Atty. Dkt. No.00100-0387-PCT

[0032] In reactive capture systems, CO2 capture and upgrade are instead combined into a single system (FIG.1A). Reactive capture can be driven electrochemically, leading to the production of syngas, CO, and ethylene. Bipolar membrane (BPM) electrolyzers with Ag cathode catalysts have been used for carbonate reduction, their CO Faradaic efficiency (FE) < 25%, cell voltages > 3.7 V at 100 mA cm–2, and consequent energy efficiencies (EE) reaching 39% at 100 mA cm–2and declining < 35% at 300 mA cm–2. (Li, Y. C. et al. ACS Energy Letters 4, 1427-1431 (2019).)

[0033] The present Example describes a study of the mechanistic origins of low CO FE in prior carbonate-to-syngas systems such as those described above. Experiments and results are further provided demonstrating a solution to this problem using certain catalyst supports, including a polydopamine (PDA)-coated hierarchically-porous (HP) carbon support.

[0034] Methods

[0035] Electrode preparation

[0036] All reagents used in this Example were purchased from suppliers without further purification. The planar carbon (Vulcan XC 72R), nanoporous carbon (Ketjenblack EC- 300J), and hierarchically porous carbon (Ketjenblack EC-600JD) were all purchased from Fuel Cell Store as used as the carbon support. The polydopamine coating on carbon supports was carried out using a solution of dopamine hydrochloride (1 mg mL−1, Sigma-Aldrich) with pH 8.5 tris-HCl buffer (10 mM Trizma®base, Sigma-Aldrich and hydrochloric acid, 37%, Sigma-Aldrich). Briefly, carbon supports (0.5 mg mL−1) were added into the solution, and the thickness of the polydopamine coating was roughly proportional to the coating time. The coated sample was washed using distilled water several times to remove unreacted precursors. After filtering, the coated samples were dried in a vacuum oven (80 °C) overnight. The catalyst ink was prepared by dispersing CoPc (cobalt phthalocyanine, Sigma- Aldrich) and polydopamine-treated carbon supports in 2-propanol with added Nafion ionomer by ultrasonication. The ink was well-sonicated for a good dispersion of CoPc catalyst. The mass ratio of the powders (CoPc and carbons) and ionomer was 9:1. The mass loading of carbon was optimized. The ink was then airbrushed onto a hydrophilic carbon substrate (Freudenberg H23, Fuel cell store) to a final loading of ~2 mg cm−2.

[0037] NiFeOxelectrode was prepared from a modified method. Briefly, Ni foam was first cleaned by 6 M HCl and DI-water for 15 min under sonication. Then, a 40 mL solution with 4 mmol NH4F, 10 mmol urea, 2 mmol Ni(NO3)2^6H2O, and 2 mmol Fe(NO3)3^9H2OAtty. Dkt. No.00100-0387-PCT was prepared and transferred to a 50 mL Teflon-lined stainless steel autoclave. The hydrothermal growth of the hydroxides on Ni foam was performed at 120 °C for 6 hours with a heating rate of 3 °C min−1, followed by sonication in DI-water and drying in the oven at 80 °C.

[0038] Electrochemical measurements

[0039] The carbonate electrolyzer contained two stainless steel flow-field plates with serpentine channels, PTFE and silicone gaskets, and the membrane electrode assembly (MEA), which contained two electrodes and a membrane, and was formed after assembling the cell hardware. The catholyte and anolyte were circulated by peristaltic pumps (INTLLAB) at 15 ml min−1. The current was controlled by an Autolab potentiostat / galvanostat. The membrane used to separate catholyte and anolyte was a commercial (Fumasep FBM, Fuel Cell Store) or custom-designed BPM. The CoPc / polydopamine-coated carbon support was used as the cathode. A piece of filter membrane was inserted as the interposer layer between the cathode and cation exchange layer (CEL). The thickness of the interposer layer was 135 µm. Pore sizes of the hydrophilic interposer layer were 1.2, 3, 5, and 8 µm for the mixed cellulose ester (MCE) membrane, and 30 µm and 160 µm for the Nylon membrane. The catholyte was 1.5 M K2CO3, and the anolyte was 1 M KOH. When carbonate electrolysis was performed in the cation exchange membrane (CEM)-based electrolyzer, Nafion 117 (H+transport) was used as the membrane, 0.05 M H2SO4was used as the anolyte, and the IrO2 / Ti felt (US Research Nanomaterials, Inc., IrO2 loading: ~1 mg cm−2) was applied as the anode. All experiments were performed at room temperature.

[0040] The gas CO2reduction reaction was performed in flow electrolyzers with three compartments. Ag / AgCl (4 M KCl) and a piece of Ni foam were employed as the reference electrode and counter electrode, respectively. The cathode catalysts were airbrushed onto hydrophobic carbon paper (Freudenberg H23C3, Fuel cell store). The anion-exchange membrane (PiperION, 40 microns) was used as the membrane to separate the cathode and anode chambers.1.5 M K2CO3 was used for both catholyte and anolyte. The flow rate of CO2 was controlled by mass flow controller (Alicat). N2was used as the balance gas to adjust the partial pressure of CO2.

[0041] CV was conducted by a general three electrode configuration from −1.2 to 0.3 V (vs. Ag / AgCl) at scan rate 100 to 500 mV s−1in Ar-saturated 1.5 M K2CO3electrolyte toAtty. Dkt. No.00100-0387-PCT observe the redox behavior of cobalt sites. The EIS analysis was obtained in same cell configuration with the CV using EIS instrument (VIONIC, Metrohm) under Ar-saturated 1.5 M K2CO3 and 1.5 M KOH, as carbonate and non-carbonate conditions. Before the EIS measurement, the electrode was equilibrated around 20 min in open circuit voltage (OCV). The measurement was conducted at OCV in the frequency range from 50 mHz to 100 kHz with an AC amplitude of 5 mV.

[0042] Product analysis

[0043] The gas products (H2 and CO) were quantified by GC (Shimadzu 2014, PerkinElmer Clarus 580) equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID) equipped with a Methanizer. The calibration curve was established by analyzing the standard calibration gases with different concentrations (10–10,000 ppm). Argon (100 mL min−1) was purged as the carrier gas to carry the gas products out of the system for quantification.

[0044] The rate of H2 / CO generation (r, mol s−1) for each cycle was calculated by the following equation: r = c ^ 10−6^ [PV̇ ^ 10−6 / (RT)] where c is the H / COflow rate of the inlet gas ml min−1); p is the ambient pressure (p = 1.013 × 105Pa); R is the gas constant (R = 8.314 J mol−1K−1); T is the room temperature (293.15 K). The total amount of gas (mol) was calculated by integrating the plot of H2 / CO production rate (mol s−1) vs. reaction time (s).

[0045] The Faradaic efficiency (FEi) can be calculated by equations as follows: ^^ ^^ ^^ FE^ൌ^ ^^^ൈ 100 %where niis the moles of product i; ziis the number of electrons transferred for one product molecule; F is the Faraday constant (96,485 C mol−1); Q is the total charge passed through the electrolytic cell.

[0046] The carbon utilization can be calculated by the equations as follows: Carbon utlization ൌ ൬1 െ^^ೀమ ^^^ଶி^^ೀమ ^^^^బ^ೀమ ^ ൈ 100 % = (1-ொ^ ൈ 100 %Atty. Dkt. No.00100-0387-PCT where ^^^^ைଶis the moles of theoretical CO2can be generated from the BPM-based electrolyzer; ^^^ைଶ ^^^is the moles of gas CO2detected at the outlet; F is the Faraday constant −1(96,485 C mol ); is the total charge passed through the electrolytic cell.

[0047] Materials characterization

[0048] X-ray photoelectron spectroscopy (XPS) was carried out on a Thermo Scientific NEXSA G2 XPS spectrometer, equipped with an Al K alpha radiation source and electron flood-gun, at a pressure of 8x10−8mbar with a pass energy of 50 eV. All spectra were calibrated with the C 1s peak at 284.8 eV. Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS) was conducted by JEOL JSM-7900FLV SEM at an accelerating voltage of 10 kV with backscattered electron detection, which is equipped with a light-element X-ray detector and an Oxford Aztec energy-dispersive X-ray analysis system. Aberration corrected scanning transmission electron microscopy (STEM) images and energy- dispersive X-ray spectroscopy (EDS) mappings were taken using JEOL ARM200CF TEM equipped with dual SDD EDS detector. Transmission electron microscopy (TEM) samples were prepared by scratching the nanopowders from the cathode surface. The scratched material was dispersed in ethanol followed by drop-casting on the grid. N2 and CO2 isotherms were conducted by Micromeritics 3Flex instrument, samples were dried at 373 K under dynamic vacuum for 12 h until the pressure stabilized below 5×10-6bar. Brunauer-Emmett- Teller (BET) method was used to calculate surface area from N2adsorption isotherm. Fourier-transform infrared (FTIR) measurements were carried out using a Nicolet iS50 FTIR spectrometer equipped with a Harrick Scientific Praying Mantis DRIFTS accessory. X-ray absorption fine structure (XAFS) measurements were made at the 8C nano-probe XAFS beamline (BL8C) of Pohang Light Source (PLS-II) in the 3.0 GeV storage ring, with a ring current of 250 mA. The X-ray beam was monochromated by a Si (111) double crystal where the beam intensity was reduced by 30% to eliminate higher order harmonics. The X-ray beam was then delivered to a secondary source aperture where the beam size was adjusted to 0.3 mm (v) × 1 mm (h). A high voltage (3,000 V) was applied to ionization chambers filled with N2 / Ar mixture gases to detect X-ray intensity. XAFS spectra were collected in both transmission and fluorescence modes.

[0049] In situ Raman analysis was conducted with a Renishaw inVia Raman spectrometer using an in-house in situ cell and a ×50 water immersion lens. A CoPc / PDA-HP (polydopamine-coated hierarchically porous) catalyst support was used as the cathode inAtty. Dkt. No.00100-0387-PCT electrolytes of 1.5 M K2CO3, purged with N2 from the backside. Pt / C on carbon cloth and Ag / AgCl were used as the anode and reference electrodes. The adsorption performance for a rhodamine B dye was compared with various carbon materials.5 mg of the carbon was used to adsorb a 0.015 mM aqueous rhodamine B solution, and the remaining dye concentration was measured by UV-Vis spectra using an Agilent Technologies HP8452 spectrometer. Before the UV-Vis spectra, the dispersed carbon was collected with a syringe filter which had a polypropylene membrane (diameter 13mm, pore size 0.45mm).

[0050] DFT calculations

[0051] All spin unrestricted DFT calculations were performed by using the Vienna Ab initio Simulation Package (VASP). For all geometric optimizations, Perdew–Burke– Ernzerhof formulation of the generalized gradient approximation (GGA-PBE) was adopted to determine the exchange-correlation energy and projector augmented wave (PAW) to construct the plane wave. The cutoff energy was set to 450 eV. The DFT-D3 method of Grimme was derived from the long-range dispersion correction. All atomic coordinates were allowed to relax until the self-consistent energy and force converged to below 10−5 eV and 0.05 eV Å−1, respectively. The simulated crystal-cell (30 Å ×26.16 Å ×30 Å) was constructed periodically, and 1 × 1 × 1 k-point mesh was generated by Monkhorst-Pack scheme in the Brillouin scheme. The hydrated potassium ion clusters containing six water molecules and one potassium ion near the Co site on the CoPc was used to simply simulate the local solvation effect and field effect in the electro-CO2RR. Therefore, the CO2RR for CO included four elementary steps, as follows. ^^^^ଶ^^^ ^ ∗ ↔ ^^^^ଶ∗^^^^∗ ^ ^^ା ^ ^^ି → ^^^^^^^^∗Here, Gibbs free energy following equation:where ^^^ி், ZPE,^^^^^^^^, and TS are the contribution form electronic energy directly calculating by DFT, zero-point energy, temperature enthalpic, and entropic correction (T = 300 K), respectively. Using the computational hydrogen electrode model, the Gibbs free energy for a proton / electron [G(H++ e-)] in the electrolyte was treated by the half of the Gibbs free energy of molecule H2[0.5G(H2)].Atty. Dkt. No.00100-0387-PCT

[0052] Mechanistic origins of low CO FE in prior carbonate-to-syngas systems

[0053] Carbonate-to-syngas systems rely on the in situ generation of CO2 (i-CO2). This is achieved by reacting carbonate with H3O+from water dissociation in the BPM junction; the proton H+is then driven out of the cation-exchange layer (CEL) of the BPM. As noted above, unfortunately, to date, such reactive capture systems have suffered from low FE when current density increases beyond 100 mA cm–2.

[0054] A chemical explanation for this problem was sought by looking at the supply and utilization of i-CO2. The possibility was evaluated that the catalyst becomes starved of CO2 under higher current density conditions: indeed the i-CO2 generation rate at 100 mA cm–2was ~ 0.7 mL min–1cm–2from the BPM (data not shown). This is lower than the mass-transport limit of ~ 5 mL min–1cm–2that is required to supply CO2 at the needed rate within gas-fed CO2electrolyzers.

[0055] Stepping back, it was noted that such reactive capture must simultaneously meet two requirements: (1) a high local pH, in order to prefer CO2 reduction over HER; and (2) high CO2availability at the cathodic catalyst. The significant challenge is that these are in conflict with one another since a solution having high pH will recapture CO2 as carbonate.

[0056] Looking at the problem quantitatively, i-CO2transport and conversion in the BPM-based reactive capture system were examined (data not shown). At current density of 100-600 mA cm–2, the maximum i-CO2 supply rate and the rate of i-CO2 consumption to feed CO2-to-CO conversion were examined. CO2 starvation arose in part due to the insufficient i- CO2 supply of 0.7 mL min–1cm–2at 100 mA cm–2noted above, and it was also further exacerbated by losses of CO2due to its recapture by locally-alkaline electrolyte.

[0057] The design of porous carbon supports for i-CO2 transport to catalyst sites Strategies were sought to resolve this dilemma, including by engineering the porosity of the catalyst support. A planar support (FIG.1C, right) offered little opportunity to enhance the availability of active catalytic sites to interact with inbound i-CO2. Nanoporous carbon (FIG. 1C, middle), with a typical pore diameter of 1-2 nm, increased surface area, but the tight pores may inhibit diffusion of i-CO2. Thus, hierarchically porous carbon supports were considered. These supports had a first, larger, pore radius (mesopore radius ~ 10-20 nm, FIG. 1C, left), and a second, smaller pore radius (micropore 1-2 nm diameter). This may offer the combination of enhanced catalyst surface area, accompanied by better transport of i-CO2 to catalytically active sites.Planar (P), Nanoporous (NP), and Hierarchically Porous (HP: anAtty. Dkt. No.00100-0387-PCT admixture of 10-20 nm mesopores further interpenetrated by 1-2 nm micropores) carbon supports were therefore studied.

[0058] Brunauer–Emmett–Teller (BET) analysis showed specific surface areas of 300, 920, and 1420 m2 / g for the three carbon supports, respectively (data not shown). BET also enabled estimation of effective pore sizes and their distributions (data not shown), and was consistent, in the case of HP, with prominent porosity components at both the micropore (1-2 nm) and the mesopore (>10 nm) length scales. HP had 16 times more mesopores than micropores, a higher ratio than ~ 2.8x for P and 3.6x for NP (data not shown Scanning transmission electron microscopy (STEM) analysis (data not shown) provided qualitative evidence, in the spatial domain, of the same trend as seen in the Fourier domain via BET. Electrochemical impedance spectroscopy (EIS) (data not shown) was used to characterize the mass-transfer processes and site utilization in the porous structures and the interaction time of ions / reactants inside the pores. This was done by measuring the total capacitance, which indicates the electrochemically active surface area, along with the relaxation time constant (τo). The capacitance increased 6x moving from P to HP, while τo doubled. It was concluded that the HP porous carbon support enriched reactants within its pores, prolonged retention of reactants, and facilitated their transport deep within pores.

[0059] A test of whether CO2 was capable of reaching the catalytic sites inside each porous catalyst support was then sought. First, CO2-gas-fed systems were studied, and whether these can maintain high FE even at a low CO2 gas feed rate was tested (FIG.2A). The HP support, when functionalized using CoPc, maintained high FE (> 85%) even when the CO2 flow rate slowed to 2.5 mL min–1cm–2. This indicates that HP allowed efficient CO2 transport to its large internal surface area.

[0060] Reactive capture performance as a function porous support, and of its surface treatment

[0061] Given this transport of CO2 to the catalyst surface, reactive capture studies were then returned to, where i-CO2was supplied via the action of protons from the BPM, followed by the diffusion of the i-CO2 to the catalyst. However, FE to CO was low, 20-30%, in the case of each of the carbon supports decorated with CoPc (FIG.2B) at both low and current densities. The ratio of capacitance (Cdl) to BET surface area was examined, and a low value was found in the 0.2-0.3 range for each carbon support (FIG.2C). These results indicated that many CoPc molecules were inactive.Atty. Dkt. No.00100-0387-PCT

[0062] To address this problem, surface treatments to improve dispersion and immobilize CoPc on each carbon support were considered, including polydopamine (PDA) coatings. PDA was deposited using self-polymerization (Methods). FIG.4 is a schematic illustration of the CoPc / PDA-coated HP support. A nitrogen content of ~2 % by weight was found using elemental analysis (data not shown). TEM, XPS, EDX, and FTIR results further confirmed a PDA coating on each type of carbon support (data not shown). HRTEM (data not shown) revealed that the PDA-coating on hierarchically porous carbon (i.e., PDA-HP) led to a more spatially uniform dispersion of CoPc. The pore size and distribution did not exhibit significant change following PDA coating (data not shown).

[0063] The ratio of capacitance (Cdl) to BET area was now about 2.5 times higher (FIG. 2C), thanks to the PDA-coating, as compared to the uncoated case. This was true for each choice of carbon support. Evidence of the same increase in molecular binding affinity was also seen in total capacitance analysis in different solutions, gas CO2adsorption isothermal analysis, and dye adsorption studies (data not shown).

[0064] Another way to check that CoPc was well-dispersed for high catalytic activity involved studying the transition of the oxidation state of the active CoPc site, under the action of reductive bias, from inactive Co2+Pc to active Co1+Pc. From in situ Raman spectroscopy (FIGS.2D-2E and other data not shown), it was found that PDA coated HP led to an earlier onset potential for, as well as a more complete transition from, inactive to active CoPc states (FIG.2F). Specifically, in the case of PDA-coated HP supports, Co2+Pc was fully transformed to Co1+Pc with the application of –1.2 VRHE potential.

[0065] EXAFS was used to further examine (data not shown) how PDA influenced the electronic interaction between the Co center and the support. EXAFS showed an upshift of the white line to higher binding energy and an increase in intensity on CoPc / PDA-HP compared to the unsupported CoPc molecules (data not shown). This indicates charge transfer between Co and support and the partial oxidation of Co centers. CV showed a positive shift of the Co2+ / Co1+redox wave after coating with PDA, consistent with the presence of more-electron deficient CoPc (data not shown). In accompanying DFT studies, calculated electron-density-difference plots (data not shown) showed that CoPc lost electrons, while PDA gained electrons , in the N- and O-terminations of PDA (N-PDA and O-PDA). Also from DFT, the adsorption energies of CO2* and the formation energies of COOH* on CoPc / N-PDA and CoPc / O-PDA were lower than those for the case of pristine CoPc (data notAtty. Dkt. No.00100-0387-PCT shown). The combined experimental and computational results demonstrate that the modified electronic structure of CoPc induced by the PDA coating facilitates the binding and activation of CO2, resulting in a lower energy barrier for its conversion into CO.

[0066] Reactive capture system performance and its optimization for energy efficiency

[0067] Reactive capture systems and their optimization were then returned to, with the focus now on the hierarchically porous (HP), polydopamine-coated (PDA) carbon support (PDA-HP). As shown in FIGS.5A-5B and 6 catalyst loading (FIGS.5A and 5B) and interposer pore size (FIG.6) were optimized. As shown in FIG.7, an interposer layer ensures high FECO(compare to FIG.3A). Ultimately, an FECOof 43% at 200 mA / cm2was obtained for CoPc / PDA-HP (see FIG.3A). The FE was retained above 37% at current densities as high as 600 mA / cm2. This contrasted with both lower-porosity and uncoated supports which, at 600 mA / cm2, declined to FE in the range 10-20% (FIG.3A).

[0068] As an initial check of operating stability, the system was characterized at 100 mA / cm2for 40 hours of electrolysis. Due to interposer dissolution, the interposer was replaced at 20-hour intervals (FIG.3C). These systems retained FE > 35% as long as the interposer was periodically replaced. The CoPc catalyst itself remained stable: Co K-edge X- ray absorption spectra of the CoPc / PDA-HP catalyst after the operation indicated that CoPc was unchanged (data not shown). The mixed cellulose ester (MCE) in the interposer appeared to be the weak link. This may be addressed by using a more long-lived material, with similar hydrophobicity and porosity, to extend operating lifetime.

[0069] It was also checked whether the carbonate electrolyzer, when operated over 24 hours, can return a catholyte that is ready for further CO2 capture in a system with gas contactor (for capture) and carbonate electrolyzer (for release and upconversion to syngas). It was found that the system herein, when fed a pH 12 post-capture liquid, returned a pH 13.2 liquid for the next round of capture (data not shown). The time-averaged FE for OH- generation (FE: 35%) over this interval corresponded to the time-averaged FECO also over this 24-hour runtime.

[0070] The carbonate electrolyzer was then optimized for energy efficiency. To study the distribution of voltages, an analytic BPM electrolyzer was constructed that would allow the voltage difference to be monitored, operando, across each electrode / membrane element (data not shown). At 200 mA / cm2, the voltage across the BPM accounted for 1.8 V, fully 42% ofAtty. Dkt. No.00100-0387-PCT Vcell. The BPM was then replaced with one incorporating a nanoparticle TiO2 WD catalyst, after which, at 200 mA cm−2, VBPMdecreased to 1 V. The Ni foam anode was also coated with Ni(Fe)Ox catalyst, reducing the anode overvoltage by ~200 mV. (See FIG.3B.)

[0071] Carbon utilization of >99% in the same current density range was also observed (data not shown). Looking across both reactive capture and gas-fed CO2reduction systems (data not shown), this carbon utilization is the highest reported to date.

[0072] Conclusions

[0073] This Example is concluded by estimating syngas energy efficiency (EE) of the optimized system compared to the existing systems. In estimating a projected syngas EE, it was assumed that an efficient water electrolyzer will be employed in parallel to provide the H2 missing to make 2:1 H2:CO syngas. Because the PEM-WE has a high energy efficiency to H2, the EE of this system EE increased when the FECOin the reactive capture stage was increased. The set of improvements herein led to a projected syngas EE of 50% at 200 mA cm−2(FIG.3B) compared to EE of 39% at 200 mA / cm2in the highest-performing existing BPM-based electrified carbonate reactive capture systems (detailed comparison among prior systems, data not shown).

[0074] Estimated full system energy requirements (Table 1 and other data not shown) were compared for: i) sequential capture-and-release followed by gas-fed electrochemical CO2 upgrade; ii) sequential capture-and-release followed by reverse water-gas shift (RWGS) using H2 from an efficient water electrolyzer; iii) the integrated reactive capture approach studied herein, again with missing H2 filled in using the same water electrolyzer. The integrated approach offered the lowest projected energy in GJ / ton of syngas, its advantage deriving the avoidance of the CO2 regeneration step in sequential DAC-plus-electrolysis. Because it directly electrified the release (via CO2to CO upgrade) process, the integrated reactive capture decreased the estimated carbon intensity by 6x compared to strategies i) and ii) when these rely on fossil methane for high-temperature thermal energy for CO2release.

[0075] Table 1. Comparison of energy and carbon intensity for sequential vs. integrated processes for syngas production. DAC + RWGS, H2Carbonate Carbonate Carbonate Scenarios SOEC for from water electrolysis electrolysisAtty. Dkt. No.00100-0387-PCTCO2 0.69 0.69 0 0 regenerationAtty. Dkt. No.00100-0387-PCTa. CO2-to-CO conversions are 80% in gas CO2reduction electrolyzers.99% of CO2from the air is converted into CO in the carbonate electrolyzers. b. CO2regeneration from carbonate is powered by natural gas. c. 11 g / kWh for green electricity; 50 kg / GJ for natural gas. d. H2: CO = 2:1 If FECO< 33%, additional CO was supplied from DAC-SOEC process. When the SOEC is assumed, the EE to CO is set to 60%. The analysis does assume (as in column 1, DAC+SOEC), the need for CO2regeneration, circulation, and an air contactor. The resultant effective EE for CO is 25% in this case of “CO-infill,” the same as for the CO contributed in column 1. If FECO > 33%, additional H2 from water electrolyzer having EE for H2 of 65%. e. From literature ACS Energy Letters 4.6 (2019): 1427-1431. f. This scenario is calculated based on the experimental results in which the device shows 42% FECO, and a cell voltage of 2.6 V at 100 mA cm−2

[0076] The word "illustrative" is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as "illustrative" is not necessarily to be construed as preferred or advantageous over other aspects or designs. Further, for the purposes of this disclosure and unless otherwise specified, "a" or "an" means "one or more.”

[0077] The foregoing description of illustrative embodiments of the invention has been presented for purposes of illustration and of description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and as practical applications of the invention to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.Atty. Dkt. No.00100-0387-PCT

[0078] If not already included, all numeric values of parameters in the present disclosure are proceeded by the term “about” which means approximately. This encompasses those variations inherent to the measurement of the relevant parameter as understood by those of ordinary skill in the art. This also encompasses the exact value of the disclosed numeric value and values that round to the disclosed numeric value.

[0079] Unless otherwise indicated, and in recognition of the inherent nature of the techniques described herein, throughout the present disclosure, terms and phrases such as “absence,” “free,” “does not comprise,” etc. encompass, but do not require a perfect absence of the referenced entity.

[0080] Unless otherwise indicated, the term “type” as used herein refers to chemical formula such that a single type means the same chemical formula and different type means different chemical formula. Similarly, use of “more” as in “one or more” refers to use of different types of the relevant entity.

[0081] Throughout the present disclosure, terms such as “comprising” and the like may be replaced with terms such as “consisting” and the like.

Claims

Atty. Dkt. No.00100-0387-PCT WHAT IS CLAIMED IS:

1. An electrolyzer comprising: a cathode comprising a porous, carbon support composed of solid carbon having surfaces which define a plurality of pores distributed throughout the solid carbon, the porous, carbon support comprising a plurality of amine groups and a metal phthalocyanine catalyst distributed on surfaces of the porous, carbon support, the cathode in contact with a catholyte comprising carbonate ions; an anode in electrical communication with the cathode; a membrane between the cathode and the anode and configured to generate in situ CO2in the catholyte; and an interposer layer between the cathode and the membrane.

2. The electrolyzer of claim 1, wherein the porous, carbon support has a surface area of at least 1000 m2 / g.

3. The electrolyzer of claim 1, wherein the plurality of pores comprises mesopores and micropores.

4. The electrolyzer of claim 3, wherein a ratio of mesopores to micropores is at least 7.

5. The electrolyzer of claim 1, wherein the plurality of amine groups is provided by a polymeric coating on surfaces of the porous, carbon support and the metal phthalocyanine catalyst is distributed on the polymeric coating.

6. The electrolyzer of claim 5, wherein the polymeric coating is a polydopamine coating.

7. The electrolyzer of claim 1, wherein the metal phthalocyanine catalyst is cobalt phthalocyanine.

8. The electrolyzer of claim 1, wherein the metal phthalocyanine catalyst comprises catalytically active sites M(n-1)+Pc at a percentage as compared to a total of M(n-1)+Pc and M(n)+Pc sites of at least 90% at an applied potential of -1.2 V versus reversible hydrogen electrode.Atty. Dkt. No.00100-0387-PCT 9. The electrolyzer of claim 8, wherein the catalytically active sites are Co1+Pc sites.

10. The electrolyzer of claim 1, wherein the plurality of amine groups is provided by a polydopamine coating and the metal phthalocyanine catalyst is present at an amount in a range of from 20 to 35 weight% as compared to a total weight of the porous, carbon support comprising the polydopamine coating and the metal phthalocyanine catalyst.

11. The electrolyzer of claim 1, wherein the membrane is a bipolar membrane.

12. The electrolyzer of claim 1, wherein the interposer layer an average pore size in a range from 5 ^m to 15 ^m.

13. The electrolyzer of claim 1, wherein the catholyte comprises an aqueous alkali metal carbonate solution.

14. The electrolyzer of claim 1, wherein the plurality of pores comprises mesopores and micropores; wherein the plurality of amine groups is provided by a polydopamine coating on surfaces of the porous, carbon support and the metal phthalocyanine catalyst is distributed on the polydopamine coating; and wherein the metal phthalocyanine catalyst is cobalt phthalocyanine.

15. The electrolyzer of claim 14, wherein a ratio of mesopores to micropores is at least 7.

16. The electrolyzer of claim 15, wherein the cobalt phthalocyanine catalyst comprises catalytically active sites Co1+Pc at a percentage as compared to a total of Co1+Pc and Co2+Pc sites of at least 90% at an applied potential of -1.2 V versus reversible hydrogen electrode.

17. The electrolyzer of claim 16, wherein the cobalt phthalocyanine catalyst is present at an amount in a range of from 20 to 35 weight% as compared to a total weight of the porous, carbon support comprising the polydopamine coating and the cobalt phthalocyanine catalyst.Atty. Dkt. No.00100-0387-PCT 18. The electrolyzer of claim 17, wherein the membrane is a bipolar membrane and the interposer layer an average pore size in a range from 5 ^m to 15 ^m.

19. A method for producing CO, the method comprising generating the in situ CO2in the catholyte of the electrolyzer of claim 1 and reducing the in situ CO2 to CO at the cathode.

20. The method of claim 19, further comprising combining the CO with H2to produce syngas.

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