WO2025175083A1 - High performance electrochemical reduction of carbon dioxide to carbon monoxide - Google Patents

Abstract

A CuZn₄ ordered intermetallic catalyst for high performance, and highly selective, CO₂ reduction to CO. CO is a valuable building block for the production of fuels and chemicals, and the electrochemical reduction of CO₂ to CO offers a sustainable and potentially cost-effective way to produce these products. Further, the production of CO can be used as a means of storing renewable energy. By converting excess renewable energy into CO, it can be stored and transported easily, and when needed, it can be converted back into energy in the form of electricity or fuels.

Description

HIGH PERFORMANCE ELECTROCHEMICAL REDUCTION OF CARBON DIOXIDE

TO CARBON MONOXIDE

GOVERNMENT SUPPORT CLAUSE

[0001] This invention was made with government support under grant CHE-2102648 awarded by the National Science Foundation. The government has certain rights in the invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application No. 63/554,241, filed February 16, 2024, the contents of which are incorporated herein by reference in their entirety.

BACKGROUND

[0003] Carbon dioxide (CO2) is a major contributor to global warming and climate change. By capturing and reducing CO2 emissions, the electrochemical reduction of CO2 to carbon monoxide (CO), ethylene gas (C2H4), and ethanol (C2H5OH) can help mitigate the impacts of climate change. Additionally, CO is a valuable building block for the production of fuels and chemicals, and the electrochemical reduction of CO2 to CO offers a sustainable and potentially cost-effective way to produce these products. Further, by using renewable energy sources to power electrochemical processes, such as wind, solar or hydropower energy, the overall carbon footprint of the fuels and chemicals produced can be significantly reduced. As of September 2021 , the global market for CO as a building block for chemicals was estimated to be around $10 billion.

[0004] Advantageously, the electrochemical reduction of CO2 to CO can help with energy storage. Excess renewable energy, which cannot be stored easily, can be used to convert CO2 into CO, which can be stored and transported easily, and when needed, the CO can be converted back into energy in the form of electricity or fuels.

[0005] There continues to be a need for an efficient and scalable solution that can meet the growing demand for CO derived from clean and/or renewable energy sources. The catalysts described herein address the needs required for the electrochemical reduction of CO2 to CO to be a viable method for mitigating climate change, reducing our dependence on fossil fuels, and advancing sustainable energy and chemical production. SUMMARY

[0006] In some aspects, a membrane electrode assembly (MEA) comprising an electrode comprising ordered intermetallic CuZni catalyst, is described.

In some other aspects, a process of using a membrane electrode assembly (MEA) to convert carbon dioxide (CO2) to carbon monoxide (CO) is described, said process comprising: passing a gas source comprising CO2 through the MEA to interact with a CuZ -electrolyte interface; and applying a voltage below the reduction potential of CO2 to the CuZm catalyst, wherein the CO2 is reduced to CO gas, wherein the MEA comprises an electrode comprising ordered intermetallic CuZru catalyst.

[0007] In some other aspects, a gas diffusion electrode (GDE) comprising a porous gas diffusion layer (GDL) and a layer of ordered intermetallic CuZi is described.

[0008] In other aspects, a method of electrodepositing intermetallic CuZi on a substrate is described, said process comprising: reducing Cu²⁺ and Zn²⁺ from an electrodeposition solution onto a substrate using electricity, wherein the electrodeposition solution is an aqueous solution comprising at least one copper (II) salt, at least one zinc (II) salt, and at least one additional component.

[0009] Other aspects, features and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE FIGURES

[0010] Figure 1. Schematic of CO2 reduction to CO using a gas diffusion cathode. The CuZ is supported on a gas diffusion layer (GDL). Figure 1 illustrates only the principal half-reaction of this device - the anode was omitted for clarity.

[0011] Figure 2. CO2 reduction performance of unoptimized CuZru electrodes. The dominant product is CO.

[0012] Figure 3. Current density (I) vs. time curve for electrodeposited 8-CuZn4.

[0013] Figure 4. X-ray diffraction (XRD) of electrodeposited s-CuZru.

[0014] Figure 5. Partial current density of H2 and CO for £-CuZn4. [0015] Figure 6. Cyclic voltammograms of £-CuZn4 at different scan rates.

[0016] Figure 7. Linear correlation between non-faradaic current density and scan rate of 8- CuZn4.

[0017] Figure 8. Scanning electron micrographs (SEM) cross-section of 8-CuZiii.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0018] Although the claimed subject matter will be described in terms of certain embodiments, other embodiments, including embodiments that do not provide all of the benefits and features set forth herein, are within the scope of this disclosure as well. Various structural and parameter changes may be made without departing from the scope of this disclosure.

Definitions

[0019] 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. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the present disclosure. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.

[0020] “About” and “approximately” are used to provide flexibility to a numerical range endpoint by providing that a given value may be “slightly above” or “slightly below” the endpoint without affecting the desired result, for example, +/- 5%.

[0021] The phrase “in one embodiment” or “in some embodiments” as used herein does not necessarily refer to the same embodiment, though it may. Furthermore, the phrase “in another embodiment” as used herein does not necessarily refer to a different embodiment, although it may. Thus, as described below, various embodiments of the invention may be readily combined, without departing from the scope or spirit of the invention.

[0022] The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional acts or structures. The singular forms “a,” “and” and “the” include plural references unless the context clearly dictates otherwise. The present disclosure also contemplates other embodiments “comprising,” “consisting of” and “consisting essentially of,” the embodiments or elements presented herein, whether explicitly set forth or not. [0023] For the recitation of numeric ranges herein, each intervening number there between with the same degree of precision is explicitly contemplated. For example, for the range of 6-9, the numbers 7 and 8 are contemplated in addition to 6 and 9, and for the range 6.0-7.0, the number 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, and 7.0 are explicitly contemplated.

[0024] As used herein, a “system” refers to a plurality of real and/or abstract elements operating together for a common purpose. In some embodiments, a “system” is an integrated assemblage of hardware and/or software elements. In some embodiments, each component of the system interacts with one or more other elements and/or is related to one or more other elements. In some embodiments, a system refers to a combination of components and software for controlling and directing methods.

[0025] As used herein, the term “substantially free,” when used in the context of a composition or component of a composition that is substantially absent, is intended to refer to an amount that is then about 1 % by weight, e.g., less than about 0.5 % by weight, less than about 0.1 % by weight, less than about 0.05 % by weight, or less than about 0.01 % by weight of the stated material, based on the total weight of the composition.

[0026] As used herein, “clean and/or renewable energy sources” include, but are not limited to, wind energy, solar energy, hydropower energy, tidal energy, and geothermal energy.

Electrolysis system and process of making and/or using same

[0027] The electrochemical reduction of CO2 to CO has the potential to be an attractive solution for reducing greenhouse gas emissions and producing valuable chemicals, but there are still several challenges that need to be addressed before it can be commercialized on a large scale. Some of the main issues are cost of the catalyst and scale up of the electrodes. The frontrunner technology presently being used in pilot plants is silver (Ag) [Krause, 2020]. Disadvantageously, the cost of the silver catalyst, is prohibitively high and the production method relies on spray-coating the silver onto a catalyst layer, which is imprecise and inconsistent, often resulting in dead zones. Furthermore, Ag is easily poisoned by impurities in the gas or electrolyte stream. Another efficient catalyst comprises gold (Au), but gold is scarce and expensive. Therefore, there is a need for alternative materials which are lower in cost, resistant to poisoning species, and can be manufactured via scalable methods to meet the market demand.

[0028] Cu-Zn bimetallic is a prospective alloy as a catalyst for producing Cl and C2 products but unfortunately the performance of the catalyst depends on composition and phase, which is not yet understood, and the widespread application of these catalysts is hindered by complicated fabrication processes, which impede the scalability of the technology [Feng, 2018; Wan, 2022; Yin, 2018; Baek, 2022],

[0029] Towards that end, the present invention relates broadly to an electrolysis system comprising ordered intermetallic CuZn4 (henceforth referred to as CuZ ), a highly efficient and cost-effective catalyst that enables the electrochemical reduction of CO2 into valuable CO. In some embodiments, the electrolysis system comprises a membrane electrode assembly (MEA) comprising ordered intermetallic CuZ . In some embodiments, the intermetallic CuZn4 further comprises a negligible amount of oxygen, e.g., on the surface of the catalyst, hi some embodiments, the CuZ comprises ordered intermetallic 8-CuZn4. In some embodiments, the CuZn4 catalyst is used to electrochemically reduce CO2 into valuable CO using electricity as the energy source. In some embodiments, the electricity is renewable electricity.

[0030] As shown in Figure 1, in some embodiments, to catalyze the chemical reaction, CO2 is passed through a gas diffusion electrode (GDE) comprising a gas diffusion layer (GDL) and a layer of CuZn4. In some embodiments, the GDL comprises a porous material comprising carbon, e.g., porous carbon paper, allowing the gas to interact with the CuZm-electrolyte interface. In some other embodiments, the GDL comprises at least one of stainless steel, silver foil, or glassy carbon. In some embodiments, the electrolyte comprises an alkaline solution, e.g., potassium hydroxide. Advantageously, this innovative catalyst and process of using same can be used at room temperature and atmospheric pressure, simplifying production and eliminating the need for expensive temperature and pressure controls. In some embodiments, the process is carried out at a temperature of about 5°C to about 90°C. In some embodiments, the process is carried out at a temperature of about 15°C to about 30°C. In some embodiments, the process is carried out at a temperature of about room temperature. When a voltage below the reduction potential of CO2 is applied to the catalyst, the CO2 is selectively converted to CO gas through reduction, which has profound implications for the future of sustainable manufacturing and offers a promising path towards a more sustainable and carbon-neutral future. In some embodiments, the half-reaction described herein (i.e., the selective CO2 reduction to CO at a cathode) is independent of the counter electrode reaction at the anode.

[0031] In some embodiments, the current density for CO production is at least 100 mA cm'², while maintaining CO selectivity. In some embodiments, the current density for CO production is in a range from about 100 mA cm"² to about 800 mA cm"², while maintaining CO selectivity. In some embodiments, the current density for CO production is in a range from about 100 mA cm"² to about 500 mA cm"², while maintaining CO selectivity. In some embodiments, the current density for CO production is in a range from about 300 mA cm"² to about 500 mA cm"², while maintaining CO selectivity. In some embodiments, the electrolysis system and process described herein comprising the CuZ can achieve a CO2 reduction having a CO selectivity of at least about 70%, or at least about 75%, or at least about 80%, or at least about 85%, in a potential range from about -0.60 to -0.90 vs RHE. In some embodiments, the electrolysis system and process described herein comprising the CuZiu can achieve a CO2 reduction having a CO to H2 selectivity of at least about 70%, or at least about 75%, or at least about 80%, or at least about 85%, in a potential range from about -0.60 to -0.90 vs RHE.

[0032] In some embodiments, the current density for CO production is at least 100 mA cm"², while maintaining CO selectivity. In some embodiments, the current density for CO production is in a range from about 100 mA cm"² to about 800 mA cm"², while maintaining CO selectivity. In some embodiments, the current density for CO production is in a range from about 100 mA cm"² to about 500 mA cm"², while maintaining CO selectivity. In some embodiments, the current density for CO production is in a range from about 300 mA cm"² to about 500 mA cm"², while maintaining CO selectivity. In some embodiments, the electrolysis system and process described herein comprising the CuZiii can achieve a CO2 reduction having a CO selectivity of at least about 70%, or at least about 75%, or at least about 80%, or at least about 85%, in a potential range from about -0.60 to -0.90 vs RHE. In some embodiments, the electrolysis system and process described herein comprising the CuZ can achieve a CO2 reduction having a CO to H2 selectivity of at least about 70%, or at least about 75%, or at least about 80%, or at least about 85%, in a potential range from about -0.60 to -0.90 vs RHE.

[0033] In some embodiments, the geometric area of the CuZn4 catalyst (e.g., as electrodeposited on a GDL), is about 1 cm² to about 10 nr or more. In some embodiments, the geometric area of the CuZn4 catalyst is about 1 cm² to about 5 cm², or about 5 cm² to about 10 cm², or about 10 cm² to about 25 cm², or about 25 cm² to about 50 cm², or about 50 cm² to about 100 cm², or about 100 0 cm to about 500 cm , or about 500 cnr to about 1 m“, or about 1 m to about 10 nr, as readily determined by the person skilled in the art.

[0034] In some embodiments, the CuZii4 catalyst has a Cu/Zn ratio of in a range of about 0.15 to about 0.35. In some other embodiments, the CuZiu catalyst has a Cu/Zn ratio of in a range of about 0.20 to about 0.30. In some other embodiments, the CuZn4 catalyst has a Cu/Zn ratio of in a range of about 0.23 to about 0.27. In some other embodiments, the CuZn4 catalyst has a Cu/Zn ratio of about 0.25. In some embodiments, the CuZn4 catalyst described herein does not electrochemically reduce CO2 to substantial amounts of formic acid, formaldehyde, methanol, methane or C2 (i.e., two carbon atoms) products. In some other embodiments, the CuZii4 catalyst described herein electrochemically reduces CO2 selectively to a product comprising CO, wherein the product comprises, cumulatively, less than about 5 wt% formic acid, formaldehyde, methanol, methane and C2 products, based on the total weight of the product. In some other embodiments, the CuZn4 catalyst described herein electrochemically reduces CO2 selectively to a product comprising CO, wherein the product comprises, cumulatively, less than about 2 wt% formic acid, formaldehyde, methanol, methane and C2 products, based on the total weight of the product. In some other embodiments, the CuZn4 catalyst described herein electrochemically reduces CO2 selectively to a product comprising CO, wherein the product comprises, cumulatively, less than about 1 wt% formic acid, formaldehyde, methanol, methane and C2 products, based on the total weight of the product. In some other embodiments, the CuZn4 catalyst described herein electrochemically reduces CO2 selectively to a product comprising CO, wherein the product comprises, cumulatively, less than about 0.1 wt% formic acid, formaldehyde, methanol, methane and C2 products, based on the total weight of the product. In some embodiments, the C Zn i catalyst is not annealed prior to use. In some embodiments, the CuZii4 catalyst is substantially free of at least one of Ag, Au, SnO, CuO_x, Ni/MgO, Pd, Sn, In, Co, and any combination thereof.

[0035] Accordingly, in one aspect, a membrane electrode assembly (MEA) comprising an electrode comprising ordered intermetallic CuZn4 catalyst is described. In some embodiments, the electrode is a gas diffusion electrode (GDE). In some embodiments, the GDE comprises a gas diffusion layer (GDL) comprising a porous material that permits passage of CO2 and CO gases. In some embodiments, the GDL comprises carbon. In some embodiments, the CuZru catalyst is electrodeposited onto the GDL. In some embodiments, the CuZn4 catalyst is electrodeposited as a film. In some embodiments, the CuZ catalyst comprises ordered intermetallic s-CuZn4. In some embodiments, the CuZm catalyst is substantially free of at least one of Ag, Au, ZnO, SnO, CuO_x, Ni/MgO, Pd, Sn, In, Co, and any combination thereof. In some embodiments, the CuZn4 catalyst has a Cu/Zn ratio of in a range of about 0.15 to about 0.35. In some embodiments, the CuZn i catalyst is not annealed.

[0036] In yet another aspect, a gas diffusion electrode (GDE) comprising a porous gas diffusion layer (GDL) and a layer of ordered intermetallic CuZ is described. In some embodiments, the GDL comprises carbon. In some embodiments, the CuZn4 catalyst is electrodeposited onto the GDL. In some embodiments, the CuZ catalyst is electrodeposited as a film. In some embodiments, the CuZi catalyst is substantially free of at least one of Ag, Au, SnO, CuO_x, Ni/MgO, Pd, Sn, In, Co, and any combination thereof. In some embodiments, the CuZn4 catalyst has a Cu/Zn ratio of in a range of about 0.15 to about 0.35. In some embodiments, the CuZn4 is not annealed.

[0037] In another aspect, a process of using a membrane electrode assembly (MEA) to convert carbon dioxide (CO2) to carbon monoxide (CO) is described, wherein the MEA comprises an electrode comprising ordered intermetallic CuZiu catalyst, said process comprising: passing a gas source comprising CO2 through the MEA to interact with a CuZ -electrolyte interface; and applying a voltage below the reduction potential of CO2 to the CuZn4 catalyst, wherein the CO2 is reduced to CO gas.

[0038] It is understood that carbon dioxide can be captured from any gas source. For example, and without limitations, the gas source can comprise ambient air, industrial gas source, substantially high concentration carbon dioxide, or any combination thereof. In still further embodiments, the gas source is ambient air. In other embodiments, the gas source is an industrial gas source. In still further embodiments, the gas source is a substantially high concentration of carbon dioxide. It is understood that the ambient air includes indoor and outdoor air. In still further embodiments, it is understood that industrial gas sources include any waste gas stream, any gas stream that is a by-product of any manufacturing processes, or a by-product of any industrial processes. In some embodiments, the gas source is obtained from various industrial sources that release carbon dioxide, including carbon dioxide from combustion gases of fossil-fueled power plants, e.g., conventional coal, oil and gas power plants, or IGCC (Integrated Gasification Combined Cycle) power plants that generate power by burning syngas; cement manufacturing plants that convert limestone to lime; orc processing plants; fermentation plants; and the like. In some embodiments, the gas source may comprise other gases, e.g., nitrogen, oxides of nitrogen (nitrous oxide, nitric oxide), sulfur and sulfur gases (sulfur dioxide, hydrogen sulfide), and vaporized materials. In some embodiments, the gas source is scrubbed or otherwise treated to remove at least a portion of gases other than carbon dioxide prior to introduction to the GDE of the electrolysis system described herein. Yet, in other embodiments, the gas source is untreated prior to introduction to the GDE of the electrolysis system described herein.

[0039] In some embodiments, the electrolysis systems described herein are configured to continuously receive carbon dioxide gas from a gas source. In some embodiments, the electrolysis systems described herein are configured to only receive carbon dioxide gas from the gas source when excess renewable energy, which cannot be stored easily, is available. Regardless, upon introduction of the CO2 to the electrolysis system, the CO2 is converted into CO, which can be stored and transported easily, and when needed, the CO can be converted back into energy in the form of electricity or fuels. In some embodiments, negative carbon emissions are achieved using the electrolysis system described herein.

[0040] In another aspect, a method of electrodepositing CuZn4 on a substrate is described. The catalyst CuZn4 can solve the challenge of scalability since it is prepared by electrochemical deposition. Electrodeposition involves the reduction of Cu²⁺ and Zn²⁺ salts from an electrodeposition solution onto a substrate (e.g., a GDL) via electricity. The electrodeposition solution is an aqueous solution comprising at least one copper (II) salt, at least one zinc (II) salt, and at least one additional component. In some embodiments, the Cu²⁺ and Zn²⁺ salts for the electrodeposition process comprise anions selected from the group consisting of hydroxides, chlorides, bromides, iodides, sulfates, sulfites, nitrates, nitrites, phosphates, phosphites, citrates, formates, lactates, tartrates, malates, fumarates, oxalates, succinates, gluconates, ascorbates, acetates, or mixtures thereof. In some embodiments, the Cu²⁺ salt and the Zn²⁺ salt comprise the same anions. In some embodiments, the Cu²⁺ salt and the Zn²⁺ salt comprise different anions. In some embodiments, the Cu²⁺ salt comprises copper sulfate. In some embodiments, the Zn²⁺ salt comprises zinc sulfate. In some embodiments, the concentration of Cu²⁺ salts in the electrodeposition solution is in a range from about 0.05 mol L'¹ to about 1 mol L'¹, or about 0.05 mol L"¹ to about 0.5 mol L’¹, or about 0.1 mol L'¹ to about 0.4 mol L ¹ , or about 0.2 mol L'¹ to about 0.3 mol L’¹. Tn some embodiments, the concentration of Zn²⁺ salts in the electrodeposition solution is in a range from about 0.01 mol L'¹ to about 0.4 mol L’¹, or about 0.02 mol L’¹ to about 0.2 mol L ¹, or about 0.03 mol L ¹ to about 0.15 mol L ¹ , or about 0.04 mol L ¹ to about 0.1 mol L’¹. In some embodiments, the at least one additional component comprises at least one of potassium hydroxide, sodium sulfate, glycine, sodium perchlorate, and combinations thereof. In some embodiments, the at least one additional component comprises sodium sulfate and glycine, wherein the concentration of sodium sulfate is in a range from about 0.1 mol L'¹ to about 1 mol L" or about 0.2 mol L'¹ to about 0.5 mol L'¹, and the concentration of glycine is in a range from about 0.5 mol L'¹ to about 2 mol L’¹, or about 1 mol L'¹ to about 1.5 mol L’¹. In some embodiments, the pH of the electrodeposition solution is about 8.5 to about 10. In some embodiments, the pH of the electrodeposition solution is about 9 to about 9.8. It is understood by the person skilled in the art how to adjust the pH of the electrodeposition solution if not in the ideal range. For example, if the pH is too low, a hydroxide (e.g., KOH) can be added. If the pH is too high, an acid (e.g., sulfuric acid) can be added. In some embodiments, the electrodeposition process involves electrodepositing CuZn4 from the electrodeposition solution onto the substrate. In some embodiments, the electricity is sourced from a renewable source. In some embodiments, the electricity is sourced, in part, from a renewable source. Advantageously, the electrodeposition process provides precise control over the thickness and distribution of the deposited material and can be easily scaled up for larger production volumes [Sen, 2017; Wang, 2020]. In some embodiments, the electrodeposition potential is in a range from about -1.3 V to about -1.5 V versus Hg/HgO (IM NaOH). In some embodiments, the thickness of the electrodeposited CuZii4 film is about 1 pm to about 1 mm. In some embodiments, the thickness of the electrodeposited CuZii4 film is about 30 pm to about 200 pm. It should be appreciated by the person skilled in the art that the time of deposition is substantially directly proportional to the thickness of the electrodeposited film. Additionally, electrochemical deposition can provide a more homogeneous electrode structure with improved adhesion and electrochemical performance than spray coating and other deposition techniques.

[0041] In some embodiments, a method of electrodepositing intermetallic CuZn4on a substrate is described, said process comprising: reducing Cu²⁺ and Zn²⁺ from an electrodeposition solution onto a substrate using electricity, wherein the electrodeposition solution is an aqueous solution comprising at least one copper (II) salt, at least one zinc (II) salt, and at least one additional component. In some embodiments, the Cu²⁺ and Zn²⁺ salts comprise, independently, anions selected from the group consisting of hydroxides, chlorides, bromides, iodides, sulfates, sulfites, nitrates, nitrites, phosphates, phosphites, citrates, formates, lactates, tartrates, malates, fumarates, oxalates, succinates, gluconates, ascorbates, acetates, or mixtures thereof. In some embodiments, the Cu²⁺ salt and the Zn²⁺ salt comprise the same anions. In some embodiments, the Cu²⁺ salt and the Zn²⁺ salt comprise different anions. In some embodiments, the Cu²⁺ salt comprises copper sulfate. In some embodiments, the Zn²⁺ salt comprises zinc sulfate. In some embodiments, the concentration of Cu²⁺ salts in the electrodeposition solution is in a range from about 0.05 mol L'¹ to about 1 mol L’¹. In some embodiments, the concentration of Zn²⁺ salts in the electrodeposition solution is in a range from about 0.01 mol L"¹ to about 0.4 mol L'¹. In some embodiments, the at least one additional component comprises at least one of potassium hydroxide, sodium sulfate, glycine, sodium perchlorate, and combinations thereof. In some embodiments, the pH of the electrodeposition solution is about 8.5 to about 10. In some embodiments, the substrate is a porous gas diffusion layer (GDL). In some embodiments, the electrodeposition potential is in a range from about -1.3 V to about -1.5 V versus Hg/HgO (IM NaOH). In some embodiments, the thickness of the electrodeposited CuZii4 film is about 1 pm to about 1 mm.

[0042] The unique advantages of the electrolysis system and process described herein include, but are not limited to:

• The CuZn₄ catalyst can be manufactured using electrodeposition, which allows for electrode areas ranging from a few square centimeters to several square meters. The scalability of the catalyst and process of using same is due to the ease of producing the electrodeposited catalysts. This makes the CuZn₄ catalyst an attractive option for industrial-scale CO2 reduction to CO, as it can be easily scaled up to match the needs of the industrial processes.

• CuZn₄ catalysts can be tailored to have high selectivity for the electrochemical reduction of CO2 to CO. In some embodiments, the deposition parameters can be varied by altering at least one of voltage, deposition duration, pH, and/or concentration of the metal salts, to optimize the deposited CuZn₄ to maximize the CO selectively, as well as increasing the current density for CO production.

• The electrolysis system and process described herein, even if unoptimized, is able to achieve similar metrics for CO selectivity compared to Ag-based systems that are currently being tested in pilot plants. The electrolysis system and process described herein offers the potential for greater cost-cffcctivcncss (because of its lower price for raw materials) and energy efficiency, with comparable or even better selectivity to CO.

• The half-reaction described herein (i.e., CO2 reduction to CO at a cathode) is independent of the counter electrode reaction at the anode.

[0043] It is understood that carbon dioxide can be captured from any gas source. For example, and without limitations, the gas source can comprise ambient air, industrial gas source, substantially high concentration carbon dioxide, or any combination thereof. In still further embodiments, the gas source is ambient air. In other embodiments, the gas source is an industrial gas source. In still further embodiments, the gas source is a substantially high concentration of carbon dioxide. It is understood that the ambient air includes indoor and outdoor air. In still further embodiments, it is understood that industrial gas sources include any waste gas stream, any gas stream that is a by-product of any manufacturing processes, or a by-product of any industrial processes. In some embodiments, the gas source is obtained from various industrial sources that release carbon dioxide, including carbon dioxide from combustion gases of fossil-fueled power plants, e.g., conventional coal, oil and gas power plants, or IGCC (Integrated Gasification Combined Cycle) power plants that generate power by burning syngas; cement manufacturing plants that convert limestone to lime; ore processing plants; fermentation plants; and the like. In some embodiments, the gas source may comprise other gases, e.g., nitrogen, oxides of nitrogen (nitrous oxide, nitric oxide), sulfur and sulfur gases (sulfur dioxide, hydrogen sulfide), and vaporized materials. In some embodiments, the gas source is scrubbed or otherwise treated to remove at least a portion of gases other than carbon dioxide prior to introduction to the GDE of the electrolysis system described herein. Yet, in other embodiments, the gas source is untreated prior to introduction to the GDE of the electrolysis system described herein.

[0044] In some embodiments, the electrolysis systems described herein are configured to continuously receive carbon dioxide gas from a gas source. In some embodiments, the electrolysis systems described herein are configured to only receive carbon dioxide gas from the gas source when excess renewable energy, which cannot be stored easily, is available. Regardless, upon introduction of the CO2 to the electrolysis system, the CO2 is converted into CO, which can be stored and transported easily, and when needed, the CO can be converted back into energy in the form of electricity or fuels. In some embodiments, negative carbon emissions are achieved using the electrolysis system described herein.

[0045] Some of the industries that could potentially benefit from CO derived from the electrolysis system described herein include the following [Jouny, 2018]:

• Chemical industry: CO is used as a feedstock for the production of various chemicals, such as methanol, acetic acid, and other hydrocarbons, which are used in a range of applications, such as plastics, textiles, and pharmaceuticals.

• Fuel industry: CO can be used as a feedstock for the production of synthetic fuels, such as gasoline and diesel, through the Fischer-Tropsch process.

• Metal industry: CO is used as a reducing agent in the production of metals, such as iron and steel.

• Energy storage industry: CO can be converted into syngas, a mixture of hydrogen and carbon monoxide, which can be used as a feedstock for the production of synthetic natural gas (SNG).

EXAMPLE

[0046] Ordered intermetallic s-CuZ was electrodeposited on carbon paper and tested in a laboratory scale gas diffusion electrode (GDE) over a geometrical area of 1 cm² to demonstrate as a proof-of-concept that the technology is able to produce CO as intended.

Materials

[0047] Copper(II) sulfate hydrate (Puratronic, 99.999%, metals basis, Thermo Scientific), Zinc sulfate heptahydrate (ACS reagent, 99%, Sigma-Aldrich), Glycine (99+%, Cell Culture Reagent, Thermo Scientific), Sodium sulfate (ACS reagent, >99%, Sigma-Aldrich), Potassium hydroxide (99.98%, metal basis, 85%min, Thermo Scientific), Potassium hydroxide hydrate (99.995%, Supelco), Carbon diffusion paper (Freudenberg), Platinum foil (Pt, Alfa Aesar, 99.99% trace metals basis), and Anion Exchange Membrane( Fumasep FAB-PK-130) were used.

Electrodeposition of CiiZau on gas diffusion paper

[0048] s-CuZru was electrodeposited on gas diffusion paper having a surface area of 1 cm².

According to Yunfei’ s recipe, the electrolyte solution was prepared by dissolving 0.06M of CuSO4, 0.233M of Z11SO4, 1.17M of C2H5NO2, and 0.3M of Na2SO4 into 300 ml of water. The pH of the solution was adjusted to 9.5 with KOH. The deposition of 8-CuZn4 was carried out at -1.35 V vs. Hg/HgO (IM NaOH) for 600 seconds, and the current density was measured to be approximately 17 mA/cm².

Materials characterization

[0049] The Thermo Scientific Helios G4 UC Focused Ion Dual Beam device was utilized to perform Scanning Electron Microscopy (SEM). The crystal structure of each phase was examined using the Bruker Advance D8 Powder X-ray Diffractometer (XRD).

Measurement of gas and liquid products

[0050] Gas products were analyzed by GCMS-QP2020 SE (Shimadzu). Gas products were collected every ten minutes. The total flow rate was 10 seem (3 through the GDE, 7 seem to dilute the gas) at a back pressure of -0.26 PSIG. NMR tests were performed on a Bruker Avance 400 MHz Spectrometer. To prepare the sample, 0.5ml of catholyte, 0.1ml of D2O, and 1.86pl of DMSO as an internal standard are used.

Electrosynthesis of s-CuZn4 at room temperature

[0051] Intermetallic 8-CuZn4 thin films were prepared by po ten tio static electrodeposition, and a current density vs. time curve is shown in Figure 3. This phase was verified by XRD (Figure 4).

CO2 reduction reaction (RR) performances in a flow cell

[0052] To investigate the correlation between intermetallic phase and catalytic performance in the reduction of CO2, experiments were conducted using 8-CuZn4 over the gas diffusion electrodes in a flow cell with a flow rate of 3 seem into GDE and gas dilution at 7 seem. To determine the reproducibility of the samples, each potential was tested three times using three fresh samples for each phase. The electrolyte used to evaluate the electrocatalytic performance was IM KOH. Figures 2 and 5 illustrate, respectively, the Faradaic Efficiency (FE) and geometric partial current density for major products of s-CuZ as a function of cathode potential. The results indicate that s-CuZn4 exhibits a stable and reliable CO2 to CO formation. Further, s-CuZn4 displays a consistent CO Faradaic efficiency of around 80%, spanning a potential range from -0.64 to -0.87 vs RHE (Figure 2). Moreover, the highest partial current density for CO production was observed at -0.87 vs. RHE, with a CO partial current density of 87.81 mA/cm² (Figure 5).

Electrochemically active surface area (ECSA) and SEM

[0053] To obtain the ECSA, the double-layer capacitance of e-CuZiu was measured in an H-cell containing an electrolyte with He-saturated 8 molal (m) NaCIC . The cyclic voltammograms with different scan rates were tested, and the linear correlation between non-faradaic current density and scan rate was accessed. The slope of the line is the double-layer capacitance, which was determined to be 3.980 mF/cm².

[0054] 8-CuZn4 had a substantial electrochemically active surface area, measuring approximately 188.09 cm². This is evident in the SEM images (Figure 8), where CuZn4 displays a rough surface having a thickness of 55.24 (±5.798) pm.

[0055] In conclusion the electrodeposited s-CuZn4 was highly selective for CO formation with a 79% FEco and a partial current density of 87.8ma/cm² at -0.87 vs. RHE. The highest FEco of 82% was observed at -0.72 V vs. RHE, with a partial current density of 61.01 mA/cm².

REFERENCES:

Baek, Y., et al., Electrochemical carbon dioxide reduction on copper-zinc alloys: ethanol and ethylene selectivity analysis. J. Mater. Chem. A 10, 9393-9401 (2022).

Feng, Y., et al., Laser-Prepared CuZn alloy Catalyst for Selective Electrochemical Reduction of CO2 to Ethylene. Langmuir 34, 13544-13549 (2018).

Jouny, M., Luc, W. & Jiao, F. General Techno-Economic Analysis of CO2 Electrolysis Systems. Industrial & Engineering Chemistry Research 57, 2165-2177 (2018).

Krause, R. et al. Industrial Application Aspects of the Electrochemical Reduction of CO2 to CO in Aqueous Electrolyte. Chemie Ingenieur Technik 92, 53-61 (2020).

Sen, S. et al. Pulsed Electrodeposition of Tin Electrocatalysts onto Gas Diffusion Layers for Carbon Dioxide Reduction to Formate. MRS Advances 2, 451-458 (2017).

Wan, L., et al., Bimetallic Cu-Zn Catalysts for Electrochemical CO2 Reduction: Phase-Separated versus Core-Shell Distribution. ACS Catal. 12, 2741-2748 (2022).

Wang, Y. & Hall, A.S. Pulsed Electrodeposition of Metastable Pd31Bil2 Nanoparticles for Oxygen Reduction Electrocatalysis. ACS Energy Letters 5, 17-22 (2020).

Yin, G., et al., A Cu-Zn nanoparticle promoter for selective carbon dioxide reduction and its application in visible-light-active Z-scheme systems using water as an electron donor. Chem. Commun. 54, 3947-3950 (2018).

Claims

CLAIMS What is claimed is:

1. A membrane electrode assembly (MEA) comprising an electrode comprising ordered intermetallic CuZru catalyst.

2. The MEA of claim 1, wherein the electrode is a gas diffusion electrode (GDE).

3. The MEA of claim 2, wherein the GDE comprises a gas diffusion layer (GDL) comprising a porous material that permits passage of CO2 and CO gases.

4. The MEA of claim 3, wherein the GDL comprises carbon.

5. The MEA of any of the preceding claims, wherein the CuZru catalyst is electrodeposited onto the GDL.

6. The MEA of claim 5, wherein the CuZn4 catalyst is electrodeposited as a film.

7. The MEA of any of the preceding claims, wherein the CuZn4 catalyst comprises ordered intermetallic s-CuZru.

8. The MEA of any of the preceding claims, wherein the CuZn4 catalyst is substantially free of at least one of Ag, Au, ZnO, SnO, CuO_x, Ni/MgO, Pd, Sn, In, Co, and any combination thereof.

9. The MEA of any of the preceding claims, wherein the CuZn4 catalyst has a Cu/Zn ratio of in a range of about 0.15 to about 0.35.

10. The MEA of any of the preceding claims, wherein the CuZii4 catalyst is not annealed.

11. A process of using the MEA of any of claims 1-10 to convert carbon dioxide (CO2) to carbon monoxide (CO), said process comprising: passing a gas source comprising CO2 through the MEA to interact with a CuZru-electrolyte interface; and applying a voltage below the reduction potential of CO2 to the CuZiu catalyst, wherein the CO2 is reduced to CO gas.

12. The process of claim 11, wherein renewable energy is used to power the process.

13. The process of claims 11-12, wherein the reduction occurs at room temperature and atmospheric pressure.

14. The process of any of claims 11-13, wherein a current density for CO production is in a range of about 100 mA cm'² to about 500 mA cm’².

15. The process of any of claims 11-14, wherein the selectivity of CO2 reduction to CO gas is at least about 70%.

16. The process of any of claims 11-15, wherein the CuZn4 catalyst does not electrochemically reduce CO2 to substantial amounts of formic acid, formaldehyde, methanol, methane or C2 products.

17. The process of any of claims 11-16, wherein the CuZn4 catalyst electrochemically reduces CO2 selectively to a product comprising CO, wherein the product comprises, cumulatively, less than about 5 wt% formic acid, formaldehyde, methanol, methane and C2 products, based on the total weight of the product.

18. The process of any of claims 11-17, wherein the gas source the gas source can comprise ambient air, industrial gas source, substantially high concentration carbon dioxide, or any combination thereof.

19. The process of any of claims 11-18, configured to continuously receive carbon dioxide gas from the gas source.

20. The process of any of claims 11-19, configured to receive carbon dioxide gas from the gas source when excess renewable energy is available.

21. A gas diffusion electrode (GDE) comprising a porous gas diffusion layer (GDL) and a layer of ordered intermetallic CuZn4.

22. The GDE of claim 21, wherein the GDL comprises carbon.

23. The GDE of claims 21 or 22, wherein the CuZ catalyst is electrodeposited onto the GDL.

24. The GDE of claim 23, wherein the CuZn4 catalyst is electrodeposited as a film.

25. The GDE of any of claims 21-24, wherein the CuZiu catalyst is substantially free of at least one of Ag, Au, SnO, CuO_x, Ni/MgO, Pd, Sn, In, Co, and any combination thereof.

26. The GDE of any of claims 21-25, wherein the CuZn4 catalyst has a Cu/Zn ratio of in a range of about 0.15 to about 0.35.

27. The GDE of any of claims 21-26, wherein the CuZn4 is not annealed.

28. A method of electrodepositing intermetallic CuZn4 on a substrate, said process comprising: reducing Cu²⁺ and Zn²⁺ from an electrodeposition solution onto a substrate using electricity, wherein the electrodeposition solution is an aqueous solution comprising at least one copper (II) salt, at least one zinc (II) salt, and at least one additional component.

29. The method of claim 28, wherein the Cu²⁺ and Zn²⁺ salts comprise, independently, anions selected from the group consisting of hydroxides, chlorides, bromides, iodides, sulfates, sulfites, nitrates, nitrites, phosphates, phosphites, citrates, formates, lactates, tartrates, malates, fumarates, oxalates, succinates, gluconates, ascorbates, acetates, or mixtures thereof.

30. The method of claims 28-29, wherein the Cu²⁺ salt and the Zn²⁺ salt comprise the same anions.

31. The method of claims 28-29, wherein the Cu²⁺ salt and the Zn²⁺ salt comprise different anions.

32. The method of any of claims 28-31, wherein the Cu²⁺ salt comprises copper sulfate.

33. The method of any of claims 28-31, wherein the Zn²⁺ salt comprises zinc sulfate.

34. The method of any of claims 28-33, wherein the concentration of Cu²⁺ salts in the electrodeposition solution is in a range from about 0.05 mol L'¹ to about 1 mol L'¹.

35. The method of any of claims 28-34, wherein the concentration of Zn²⁺ salts in the electrodeposition solution is in a range from about 0.01 mol L'¹ to about 0.4 mol L'¹.

36. The method of any of claims 28-35, wherein the at least one additional component comprises at least one of potassium hydroxide, sodium sulfate, glycine, sodium perchlorate, and combinations thereof.

37. The method of any of claims 28-36, wherein the pH of the electrodeposition solution is about 8.5 to about 10.

38. The method of any of claims 28-37, wherein the substrate is a porous gas diffusion layer (GDL).

39. The method of any of claims 28-38, wherein the electrodeposition potential is in a range from about -1.3 V to about -1.5 V versus Hg/HgO (IM NaOH).

40. The method of any of claims 28-39, wherein the thickness of the electrodeposited CuZn4 film is about 1 pm to about 1 mm.