Catalyst compositions and methods for electrochemical reduction of carbon dioxide

Abstract

Embodiments of the present disclosure describe catalyst compositions, methods, and systems for the electrochemical reduction of carbon dioxide (CO2). In certain embodiments, the catalyst composition may include a first metal selected from the group consisting of copper (Cu), gold (Au), silver (Ag), and any combination, alloy, or mixture thereof; a second metal selected from the group consisting of yttrium (Y), scandium (Sc), titanium (Ti), zirconium (Zr), hafnium (Hf), and any combination, alloy, or mixture thereof; and a third metal selected from the group consisting of palladium (Pd), platinum (Pt), and any combination, alloy, or mixture thereof.

Description

CATALYST COMPOSITIONS AND METHODS FOR ELECTROCHEMICAL REDUCTION OF CARBON DIOXIDEInventors: Matthew Montemore, Ming Yang, Gbolade Kayode, and Isaac SeimCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional Appl. Ser. No.63 / 712,055, entitled “Catalyst for the Electrochemical Reduction of Carbon Dioxide and Related Methods.” filed October 25, 2024, the contents of which are hereby incorporated by reference herein, in their entirety and for all purposes.STATEMENT OF GOVERNMENT INTEREST

[0002] This invention was made with government support under CHE2154952 and OIA2327308 awarded by the National Science Foundation. The government has certain rights in the invention.TECHNICAL FIELD

[0003] The present disclosure relates to compositions and methods for electrochemical reduction of carbon dioxide (CO2), particularly to the use of metal catalyst compositions for electrochemical reduction of CO2.BACKGROUND

[0004] Carbon dioxide (CO2) accumulating in the atmosphere is linked to climate change, creating an urgent need to remove existing CO2 from the air. Rather than simply storing the removed CO2, however, a better strategy may include conversion of captured CO2 into valuable chemicals like ethanol. Electrocatalytic carbon dioxide (CO2) reduction (eCCER) has emerged as a technology to mitigate greenhouse gases while converting CO2 into useful chemical feedstocks. When coupled with renewable energy sources, eCCER has the potential to achieve a carbon-neutral energy future. In the eCCER process, CO2 molecules are first activated to form *CCE , which undergoes further electrochemical proton (H+) / electron (e-) transfer processes to form either carbon monoxide (*CO) or formic acid (*HCOOH) adsorbates. To produce further hydrogenatedand multi-carbon(C2+) products, the *CO intermediate must remain on the catalyst surface as a kinetically adsorbed species to undergo additional elementary reactions, such as Cl hydrogenation, C-C coupling, and C2 hydrogenation. These steps are often the rate determining steps (RDSs) and selectivity-determining steps (SDSs) for important products like methane, ethylene, ethanol, and acetic acids.SUMMARY

[0005] Applicant has recognized that current catalyst technologies for CO2 conversion, particularly those based on copper alone, have limited efficiency in converting CO2 into valuable multi-carbon compounds and suffer from poor selectivity, making the CO2 conversion process economically challenging for large-scale implementation. Applicant also has recognized the need for more effective catalysts that achieve higher conversion rates and better selectivity to make CO2 conversion a viable solution for both reducing atmospheric greenhouse gases and producing valuable industrial feedstocks.

[0006] Accordingly, Applicant has unexpectedly developed new catalysts for the electrochemical reduction of carbon dioxide. These catalyst compositions include a combination of three metals, namely either a three-metal alloy catalyst composition or a catalyst composition in which a second metal and a third metal are doped onto an external surface of a first metal. In certain embodiments, the presently disclosed catalyst compositions may be in the form of a dualatom catalyst (DAC) which has single atoms of the second and third metals dispersed on an external surface of the first metal. In these embodiments, for example, the single atoms of the second and third metals are positioned on the surface of the first metal such that they are either directly bonded to one another or such that they are in close enough proximity to one another to be bonded through an adsorbing or bridging species such as oxygen, carbon monoxide, carbon dioxide, or formate.

[0007] These catalyst compositions can exhibit synergistic catalytic activity between the second and third metals alloyed with or doped onto the first metal. The presently disclosed catalysts have an increased efficiency and selectivity for liquid C2+ oxygenates, including ethanol. The presently disclosed catalysts offer a unique catalyst design approach for optimizing CO2 electroreduction processes which could significantly expand the design space for advanced electrocatalysts andenable deeper hydrogenation of CO2 products beyond what is achievable with monometallic or single atom alloy (SAA) catalysts.

[0008] In certain embodiments, the catalyst composition may be a trimetallic YPdCu alloy catalyst composition. The YPdCu catalyst composition has been discovered to outperform Cu-only catalyst compositions as well as YCu and PdCu catalyst compositions. In particular, Applicant has discovered that a single atom alloy of yttrium on copper (YiCu) facilitates the conversion of CO2 to CO but exhibits limited hydrogenation of CO to multi-carbon species due to its weak binding strength to CO. In contrast, Applicant has recognized that single-atom palladium on copper (PdiCu) catalyst, being electron-rich, does not significantly enhance CO2 activation but promotes C-C coupling and oxygenate formation due to enhanced local CO concentration, a critical step for multi-carbon species production and the formation of oxygenates. The present disclosure provides dual-atom alloy (DAA) catalysts which provide comparative advantages of the respective metals while mitigating the limitations of their individual single atom alloy (SAA) formulations. In an embodiment, the presence of Y 1 and Pdi species on a Cu surface significantly enhances reactivity in eCCER, effectively converting CO2 to liquid C2+ oxygenates, specifically, ethanol. The catalysts provide both high reaction rates and high selectivity to ethanol. Ethanol is a desirable product as it is a liquid, which eases transport, and can be used as a chemical feedstock for many applications including fuels and chemical synthesis. The YiPdiCu catalyst, for example, has a total current density of 172 mA / cm2and a Faradaic efficiency (FE) of 72.2% at -1.1 V vs. RHE for the production of the liquid C2+ oxygenates, significantly outperforming the Cu-only catalyst and SAA alloy formulations.

[0009] According to one aspect of the present disclosure, a catalyst composition for the electrochemical reduction of carbon dioxide is provided. The catalyst composition may include: (1) a first metal selected from the group consisting of copper (Cu), gold (Au), silver (Ag), and any combination, alloy, or mixture thereof: a second metal selected from the group consisting of yttrium (Y), scandium (Sc), titanium (Ti), zirconium (Zr), hafnium (Hf), and any combination, alloy, or mixture thereof; and (3) a third metal selected from the group consisting of palladium (Pd), platinum (Pt), and any combination, alloy, or mixture thereof. In certain embodiments, the second metal and the third metal may be doped onto an external surface of the first metal. In certain embodiments, single atoms of the second metal and single atoms of the third metal may bedispersed on an external surface of the first metal. In certain embodiments, the catalyst composition may include a metal support structure consisting of or comprising the first metal or comprising the first metal. In certain embodiments, the catalyst composition may be a dual-atom catalyst (DAC) having single atoms of the second and third metals doped into a base metal matrix to form a trimetallic alloy. In such embodiments, the base metal matrix may consist of or comprise the first metal. In certain embodiments, the single atoms of the second and third metals may be distributed throughout the base metal matrix such that they are either directly bonded to one another or in close enough proximity to one another to be bonded to each other through an absorbing species or a bridging species. The absorbing or bridging species may be, for example, oxygen, carbon monoxide, carbon dioxide, or formate. In other examples, the single atoms of the second and third metals may be positioned such that they are bonded to each other through an adsorbing carbon dioxide molecule or a bridging oxygen atom.

[0010] In certain embodiments, the catalyst may be a dual-atom catalyst (DAC) having single atoms of the second and third metals dispersed on an external surface of the first metal. In such embodiments, the single atoms of the second and third metals may be positioned on the surface of the first metal such that they are either directly bonded to one another or such that they are in close enough proximity to one another to be bonded through an adsorbing species or a bridging species such as oxygen, carbon monoxide, carbon dioxide, or formate species.

[0011] In certain embodiments, the catalyst composition may be substantially free from components other than the first metal, the second metal, and the third metal. In certain embodiments, the ratio of the second metal to the first metal is from about 1:4 to about 1:1000 on a molar basis or a weight basis. In certain embodiments, the ratio of the third metal to the first metal is from about 1:4 to about 1:1000 on a molar basis or a weight basis. In certain embodiments, the catalyst composition may include: (1) at least 60% by weight of the first metal; (2) up to 20% by weight of the second metal; and (3) up to 20% by weight of the third metal. In certain embodiments, the catalyst composition may comprise from about 98.7 wt.% to about 99.65 wt.% of the first metal, from about 0.15 wt.% to about 0.65 wt.% of the second metal, and from about 0.15 wt.% to about 0.65 wt.% of the third metal. In other embodiments, the catalyst composition may comprise from about 98 wt.% to about 99.65 wt.% of the first metal, from about 0.15 wt.% to about 1.0 wt.% of the second metal, and from about 0.15 wt.% to about 1.0 wt.% of the thirdmetal. In still other embodiments, the catalyst composition may comprise from about 90 wt.% to about 99.65 wt.% of the first metal, from about 0.15 wt.% to about 5.0 wt.% of the second metal, and from about 0.15 wt.% to about 5.0 wt.% of the third metal. In yet other embodiments, the catalyst composition may comprise from about 80 wt.% to about 99.65 wt.% of the first metal, from about 0.15 wt.% to about 10.0 wt.% of the second metal, and from about 0.15 wt.% to about 10.0 wt.% of the third metal. In some embodiments, the catalyst composition may comprise from about 60.0 wt.% to about 99.65 wt.% of the first metal, from about 0.15 wt.% to about 20.0 wt.% of the second metal, and from about 0.15 wt.% to about 20.0 wt.% of the third metal. In certain embodiments, the first metal is copper (Cu), the second metal is yttrium (Y), and the third metal is palladium (Pd).

[0012] According to certain aspects of the present disclosure, a YiPdiCu dual-atom catalyst (DAC) is provided. In certain embodiments, the YiPdiCu DAC may be substantially free from components other than the first metal (e.g., Cu), the second metal (e.g., Y), and the third metal (e.g., Pd). In certain embodiments, the ratio of Y to Cu is from about 1:4 to about 1:1000 on a molar basis or a weight basis, and the ratio of Pd to Cu is from about 1:4 to about 1:1000 on a molar basis or a weight basis. In certain embodiments, the YiPdiCu DAC composition is characterized by a total current density of at least 150 mA / cm2and a Faradaic efficiency (FE) of at least 65% at -1.1 V vs. RHE toward the production of liquid C2+ oxygenates. In certain embodiments, the YiPdiCu catalyst composition may comprise from about 98.7 wt.% to about 99.65 wt.% Cu, from about 0.15 wt.% to about 0.65 wt.% Y, and from about 0.15 wt.% to about 0.65 wt.% Pd. In other embodiments, the YiPdiCu catalyst composition may comprise from about 98 wt.% to about 99.65 wt.% Cu, from about 0.15 wt.% to about 1.0 wt.% Y, and from about 0.15 wt.% to about 1.0 wt.% Pd. In still other embodiments, the YiPdiCu catalyst composition may comprise from about 90 wt.% to about 99.65 wt.% Cu, from about 0.15 wt.% to about 5.0 wt.% Y, and from about 0.15 wt.% to about 5.0 wt.% Pd. In yet other embodiments, the YiPdiCu catalyst composition may comprise from about 80 wt.% to about 99.65 wt.% Cu, from about 0.15 wt.% to about 10.0 wt.% Y, and from about 0.15 wt.% to about 10.0 wt.% Pd. In some embodiments, the YiPdiCu catalyst composition may comprise from about 60.0 wt.% to about 99.65 wt.% Cu, from about 0.15 wt.% to about 20.0 wt.% Y, and from about 0.15 wt.% to about 20.0 wt.% Pd.

[0013] According to another aspect of the present disclosure, methods for the electrochemical reduction of carbon dioxide are provided. The methods may include, for example, electrochemically reducing a reaction mixture which includes carbon dioxide in the presence of any of the catalyst compositions. In certain embodiments, the reaction mixture may be a waste stream or other carbon dioxide-containing stream derived from one or more industrial processes, particularly industrial processes that produce significant amounts of carbon dioxide, or a carbon dioxide-containing stream that is otherwise in need of carbon dioxide reduction or mitigation.

[0014] In general, the methods, for example, may be operable to generate a product stream having one or more C2+ organic compounds. The one or more C2+ organic compounds may, for example, be selected from the group consisting of ethanol, ethylene, acetic acid, acetate, and any combination thereof. In other embodiments, the product stream produced by the methods may be a liquid product stream having one or more C2+ oxygenate compounds. The one or more C2+ oxygenate compounds may, for example, be selected from the group consisting of ethanol, acetic acid, acetate, and any combination thereof.

[0015] In certain embodiments, the liquid product stream may include at least 70% by weight ethanol. In other embodiments, the liquid product stream may include at least 95% by weight ethanol. In certain other embodiments, the methods may have a catalyst Faradaic efficiency (FE) of at least 55% at -1.1 V vs. RHE toward the production of the liquid product stream. In yet other embodiments, the methods may have a catalyst Faradaic efficiency (FE) of at least 65%, or at least 70%, or at least 72%, or at least 75% at -1.1 V vs. RHE toward the production of the liquid product stream.

[0016] In certain embodiments, the method for the electrochemical reduction of carbon dioxide also may include supplying a reaction mixture stream having carbon dioxide (CO2) to a CO2 electrolyzer or an electrochemical cell. The CO2 electrolyzer or electrochemical cell may include a working electrode or cathode and a counter electrode or anode. The working electrode or cathode may include or may be coated with any one of the presently disclosed catalyst compositions. The CO2 electrolyzer or electrochemical cell is configured to electrochemically reduce CO2, particularly when voltage is supplied to the electrodes of the electrolyzer or cell. The method may also include causing the electrochemical reduction of CO2 in the reaction mixture stream by theprovision of voltage to the electrodes and recovering a liquid product stream from the CO2 electrolyzer cell. The liquid product stream may include, for example, one or more C2+ oxygenate compounds selected from the group consisting of ethanol, acetic acid, acetate, and any combination thereof.

[0017] According to another aspect of the present disclosure, methods of preparing the catalyst compositions are provided. In certain embodiments, the catalyst compositions may be prepared by: (1) combining a second metal solution and a third metal solution with a liquid dispersion of a first metal catalyst matrix precursor to generate a liquid solution that contains a catalyst precursor solid; (2) isolating the catalyst precursor solid from the liquid solution; (3) annealing the catalyst precursor solid to produce a substantially impurity-free catalyst precursor; and (4) reducing, electrochemically, the catalyst precursor to produce the catalyst composition.

[0018] In other embodiments, the catalyst compositions may be prepared by: (1) generating a first metal catalyst precursor matrix by precipitation from a first metal chloride and NaOH solution; (2) combining a third metal chloride solution with a liquid dispersion of the first metal catalyst matrix precursor to generate a first liquid solution that contains an intermediate catalyst precursor solid; (3) combining a second metal nitrate solution with the first liquid solution to produce a second liquid solution that contains a catalyst precursor solid; (4) isolating the catalyst precursor solid from the liquid solution; (5) annealing the catalyst precursor solid to produce a substantially impurity-free catalyst precursor; and (6) reducing, electrochemically, the catalyst precursor to produce the catalyst composition. In certain embodiments, generating the first metal catalyst precursor matrix may include causing the precipitation of a first metal catalyst precursor matrix, such as through the simultaneous dropwise addition of 0.5M first metal chloride solution and 0.5M NaOH solutions into deionized water under a continuous N2 atmosphere with constant stirring at a pH of about 9.5.

[0019] In other embodiments, a method of preparing a YiPdiCu catalyst composition for the electrochemical reduction of carbon dioxide is provided. The method may include: (1) combining a PdCL solution and a Y(NO3)3-6H2O solution with a liquid dispersion of a Cu(OH)2 catalyst matrix precursor to generate a liquid solution that contains a catalyst precursor solid; (2) isolating the catalyst precursor solid from the liquid solution; (3) annealing the catalyst precursor solid toproduce a substantially impurity-free YPdCuO catalyst precursor; and (4) reducing, electrochemically, the YPdCuO catalyst precursor to produce the YiPdiCu catalyst composition.

[0020] In other embodiments, the method of preparing a YiPdiCu catalyst composition for the electrochemical reduction of carbon dioxide may include: (1) generating a Cu(OH)2 catalyst precursor matrix by precipitation from a CUC12-2H2O and NaOH solution; (2) combining a PdCb solution with a liquid dispersion of a Cu(OH)2catalyst matrix precursor to generate a first liquid solution that contains an intermediate catalyst precursor solid; (3) combining a Y(NO3)3-6H2O solution with the first liquid solution to produce a second liquid solution that contains a catalyst precursor solid; (4) isolating the catalyst precursor solid from the liquid solution; (5) annealing the catalyst precursor solid to produce a substantially impurity-free YPdCuO catalyst precursor; and (6) reducing, electrochemically, the YPdCuO catalyst precursor to produce the YiPdiCu catalyst composition. In certain embodiments, generating the Cu(OH)2 catalyst precursor matrix may include causing the precipitation of a Cu(OH)2 catalyst precursor matrix, such as through the simultaneous dropwise addition of 0.5M CuCh-2H2O and 0.5M NaOH solutions into deionized water under a continuous N2 atmosphere with constant stirring at a pH of about 9.5.

[0021] Still other aspects and advantages of these exemplary embodiments and other embodiments, are discussed in detail herein. Moreover, it is to be understood that both the foregoing information and the following detailed description provide merely illustrative examples of various aspects and embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed aspects and embodiments. Accordingly, these and other advantages and features of the present disclosure, will become apparent through reference to the following description and the accompanying drawings. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and may exist in various combinations and permutations.BRIEF DESCRIPTION OF THE DRAWINGS

[0022] These embodiments and other features, aspects, and advantages of the disclosure will be better understood in conjunction with the following descriptions, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only certain embodiments of the disclosure and, therefore, are not to be considered limiting of the scope of the disclosure.

[0023] FIG. 1 is an illustrative schematic diagram of an exemplary three-metal alloy catalyst composition, according to an embodiment of the disclosure.

[0024] FIG. 2 is an illustrative schematic diagram of an exemplary three-metal surface doped catalyst composition, according to an embodiment of the disclosure.

[0025] FIG. 3 is an illustrative schematic diagram of a CO2 electrolyzer system and electrochemical cell, according to an embodiment of the disclosure, and that may include the presently disclosed catalyst compositions and be used for or with the presently disclosed methods.

[0026] FIG.4 is an illustrative diagram of a method for the electrochemical reduction of carbon dioxide by use of the presently disclosed catalyst compositions, according to an embodiment of the disclosure.

[0027] FIG. 5 is an illustrative diagram of an exemplary method to prepare a Y iPdiCu catalyst composition for the electrochemical reduction of carbon dioxide, according to an embodiment of the disclosure.

[0028] FIG. 6 is an attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) data plot of wavenumber (cm1) versus absorbance [a.u.] for the YiPdiCu catalyst composition demonstrating obvious peaks for key reaction intermediates in the electrochemical reduction of carbon dioxide, according to an embodiment of the disclosure.

[0029] FIG.7 is a data plot showing the current density (J) [mA / cm2] for the YiPdiCu catalyst composition prepared in Example 1 as well as, for comparison, Cu, YiCu, PdiCu, and PdiCu+YiCu catalysts, according to an embodiment of the disclosure.

[0030] FIG. 8 is a data plot showing the Faradaic efficiency (FE) [%] versus V [vs. RHE] towards liquid reaction products for the YiPdiCu catalyst composition prepared in Example 1 as well as, for comparison, Cu, YiCu, and PdiCu catalysts, according to an embodiment of the disclosure.

[0031] FIG. 9 is a data plot showing the additive Faradaic efficiency (FE) [%] versus V [vs. RHE] towards liquid reaction products for the YiCu + PdiCu single atom alloy compositions,thereby confirming the synergistic interaction in the YiPdiCu catalyst composition by comparison to the data shown in FIG.8, according to an embodiment of the disclosure.

[0032] FIG. 10 is an in situ X-ray absorption near edge structure (XANES) data plot showing photon energy [eV] versus normalized absorption [a.u.] for the YiPdiCu catalyst composition prepared in Example 1, demonstrating that Cu is completely reduced from CuO to metallic Cu, according to an embodiment of the disclosure.

[0033] FIG.11 is an in situ extended X-ray absorption fine structure (EXAFS) data plot showing R [A] versus FT [k3 / (k)] for the YiPdiCu catalyst composition prepared in Example 1, demonstrating that Cu is completely reduced from CuO to metallic Cu, according to an embodiment of the disclosure.

[0034] FIG. 12 is an in situ EXAFS data plot showing R [A] versus FT [k3%(k)J for the YiPdiCu catalyst composition prepared in Example 1, as well as, for comparison purposes, PdiCu catalyst and Pd foil, confirming that Pd exists as a single atom species in the YiPdiCu catalyst prepared in Example 1, and further demonstrating that while Pd exists in a metallic state in PdiCu (due to the metallic nature of the Cu matrix), Pd in YiPdiCu is partially cationic due to the influence of nearby YiOxspecies, according to an embodiment of the disclosure.

[0035] FIG. 13A and FIG. 13B are in situ EXAFS data plots showing R [A] versus FT [k3%(k)] for the YiPdiCu catalyst composition prepared in Example 1 (FIG. 13A) and for a YiCu catalyst (FIG. 13B), respectively, confirming that Y exists as a single atom YOXspecies in the YiPdiCu catalyst prepared in Example 1. according to an embodiment of the disclosure.DETAILED DESCRIPTION

[0036] The present disclosure provides for catalysts, methods, and systems for the electrochemical reduction of carbon dioxide. So that the manner in which the features and advantages of the embodiments of the methods and systems disclosed herein, as well as others, which will become apparent, may be understood in more detail, a more particular description of embodiments of methods and systems is provided. In the following description, numerous details are set forth in order to provide a thorough understanding of the various embodiments. In other instances, well-known processes, devices, and systems may not be described in particular detail inorder not to unnecessarily obscure the various embodiments. Additionally, illustrations of the various embodiments may omit certain features or details in order to not obscure the various embodiments.

[0037] The use of the words “a” or “an” when used in conjunction with the term “comprising,” “including,” “containing,” or “having” in the claims or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.” The words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps. The term “about” is defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment the terms are defined to be within 10%, preferably, within 5%, more preferably, within 1%, and most preferably, within 0.5%. The terms “wt.%”, “vol.%” or “mol.%” refer to a weight, volume, or molar percentage of a component, respectively, based on the total weight, the total volume, or the total moles of material that includes the component. When referring to the presently disclosed catalyst compositions, or components thereof, the terms “wt.%,” “mole %,” “molar basis,” “weight basis,” and the like, refer to the catalyst composition itself and do not refer to or include any support structure or composition not made of the first metal that may be used to support the catalyst composition. In a non-limiting example, 10 moles of component in 100 moles of the material are 10 mol.% of component. The term “substantially” and its variations are defined to include ranges within 10%, within 5%, within 1%, or within 0.5%.

[0038] The present disclosure is generally directed to embodiments of catalyst compositions, methods, and systems for the electrochemical reduction of carbon dioxide. According to certain embodiments of the present disclosure, the catalyst compositions may include a three-metal alloy catalyst composition, such as exemplary three-metal alloy catalyst composition 100 shown illustrated in FIG. 1. While exemplary three-metal alloy catalyst composition 100 is illustrated in FIG. 1 as a YiPdiCu three-metal alloy catalyst composition, as disclosed herein, certain specific metals may be substituted for Y, Pd, and Cu in order to generate the three-metal alloy catalyst composition 100 having improved efficiency and selectivity when used as a catalyst for theelectrochemical reduction of carbon dioxide. In exemplary embodiments, the three-metal alloy catalyst composition 100 may include a first metal 101 selected from the group consisting of copper (Cu), gold (Au), silver (Ag). and any combination, alloy, or mixture thereof. The three-metal alloy catalyst composition 100 may also include a second metal 102 selected from the group consisting of yttrium (Y), scandium (Sc), titanium (Ti), zirconium (Zr), hafnium (Hf), and any combination, alloy, or mixture thereof. The three-metal alloy catalyst composition 100 may also include a third metal selected from the group consisting of palladium (Pd), platinum (Pt), and any combination, alloy, or mixture thereof.

[0039] According to certain embodiments of the present disclosure, the catalyst compositions may be a three-metal surface doped catalyst composition 200 in which the second metal 102 and the third metal 103 are doped onto an external surface 105 of the first metal 101, such as exemplary three-metal surface doped catalyst composition 200 shown illustrated in FIG. 2. The first metal 101, second metal 102, and third metal 103 in three-metal surface doped catalyst composition 200 may be the same metals as described above with respect to three-metal alloy catalyst composition 100 in FIG. 1. As shown in FIG. 2, three-metal surface doped catalyst composition 200 may include single atoms of the second metal 102 (e.g., Y) and single atoms of the third metal 103 (e.g., Pd) dispersed on an external surface 105 of the first metal 101 (e.g., Cu). In certain embodiments, three-metal surface doped catalyst composition 200 may also include a metal support structure 175 comprising or consisting of the first metal 101. In certain embodiments, the three-metal alloy catalyst composition 100 or the three-metal surface doped catalyst composition 200 may be a dualatom catalyst (DAC) comprising single atoms of the second metal 102 and third metal 103 doped into a base metal matrix 150 comprising the first metal 101. For example, as shown in FIG. 1 and FIG. 2, the single atoms of the second metal 102 and the third metal 103 may be distributed throughout the base metal matrix 150 such that the single metal atoms 102, 103 are either directly bonded to one another or in close enough proximity to one another to be bonded to each other through an adsorbing or bridging species, such as a carbon dioxide molecule 125 or bridging oxygen atom 135 bonded to a carbon atom 130. As shown in FIG. 2, the three-metal surface doped catalyst composition 200 may be a dual-atom catalyst (DAC) comprising single atoms of the second metal 102 and the third metal 103 dispersed on an external surface 105 of the first metal 101 with the single atoms 102, 103 of the second metal 102 and third metal 103 positioned on the surface of the first metal 101 such that they are either directly bonded to one another or in closeenough proximity to one another to be bonded to each other through an adsorbing or bridging species, such as carbon dioxide molecule 125 or bridging oxygen atom 135 bonded to a carbon atom 130. In certain embodiments, the catalyst compositions, in all of their disclosed forms, exhibit synergistic catalytic activity between the second metal 102 and the third metal 103 alloyed with or doped onto the first metal 102. As described herein, the catalysts are characterized by increased efficiency and selectivity for liquid C2+ oxygenates, including ethanol.

[0040] In certain embodiments, the catalyst compositions, such as catalyst compositions 100, 200, may be substantially free from components (e.g., other metals or other non-metal elements) other than the first metal, the second metal, and the third metal. In certain embodiments, the catalyst compositions may substantially consist of or consist essentially of the first metal, the second metal, and the third metal, without including any other metals that may affect the material properties of the catalyst composition. For example, the catalyst compositions may comprise less than 0.01 weight % (wt. %), or less than 0.1 wt.%, or less than 1 wt.%, or less than 2 wt.%, or less than 5 wt.%, or less than 10 wt.% components other than the first metal, the second metal, and the third metal. Alternatively, at least 90 wt.%, or at least 95 wt.%, or at least 98 wt.%, or at least 99 wt.%, or at least 99.9 wt.%, or at least 99.99 wt.% of the catalyst is comprised of the first metal, the second metal, and the third metal. The presently disclosed catalyst compositions may be an unsupported catalyst or may be a supported catalyst composition. For example, the catalyst composition may be used in the presently disclosed methods and systems without being supported on a separate material, including an inert separate material or support. In such instances, the catalyst composition may, for example, be used in a CO2 electrolyzer and / or an electrochemical cell without the use of any additional support or material. For example, the catalyst composition may be directly disposed on or coated onto a working electrode or cathode or the working electrode or cathode may include or be made of the catalyst composition. In other embodiments, the catalyst compositions may be in the form of a supported catalyst that is immobilized on the surface of a separate material (e.g., a support) in order to improve the activity or stability of the catalyst composition or to facilitate attachment to an electrode used in the reduction of carbon dioxide. For example, the catalyst compositions may, in certain embodiments, be supported on a support such as alumina, activated carbon, or zeolite material.

[0041] In certain embodiments, the ratio of the second metal to the first metal in the catalyst compositions may be from about 1:4 to about 1:1000 on a molar basis or on a weight basis. In certain embodiments, the ratio of the second metal to the first metal may be from about 1:4 to about 1:6, or from 1:4 to about 1:5, or from about 1:4 to about 1:8, or from about 1:4 to about 1:10, or from about 1:4 to about 1:12, or from about 1:4 to about 1:25, or from about 1:4 to about 1:50, or from about 1:4 to about 1:100, or from about 1:4 to about 1:250, or from about 1:4 to about 1:500, or from about 1:4 to about 1:750. The ratio can represent a bulk composition of the catalyst or a surface composition of the catalyst, such as when the second metal is doped on an external surface of the first metal. In embodiments in which the ratio represents a surface composition, the ratio applies to the first two atomic layers of the catalyst composition.

[0042] In certain embodiments, the ratio of the third metal to the first metal in the catalyst compositions may be from about 1:4 to about 1:1000 on a molar basis or on a weight basis. In certain embodiments, the ratio of the third metal to the first metal may be from about 1:4 to about 1:6, or from 1:4 to about 1:5, or from about 1:4 to about 1:8, or from about 1:4 to about 1:10, or from about 1:4 to about 1:12, or from about 1:4 to about 1:25, or from about 1:4 to about 1:50, or from about 1 :4 to about 1 : 100, or from about 1 :4 to about 1 :250, or from about 1 :4 to about 1 :500, or from about 1:4 to about 1:750. The ratio can represent a bulk composition of the catalyst or a surface composition of the catalyst, such as when the third metal is doped on an external surface of the first metal. In embodiments in which the ratio represents a surface composition, the ratio applies to the first two atomic layers of the catalyst composition.

[0043] In certain embodiments, the first metal may be present in the catalyst compositions in an amount of at least 60 mole %, calculated based on the number of moles of the first metal in the catalyst composition divided by the sum of the number of moles of all components in the catalyst composition, such as the number of moles of the first metal, the second metal, and the third metal in the catalyst composition, multiplied by 100%. In other embodiments, the first metal may be present in the catalyst compositions in an amount of at least 65 mole %, or at least 70 mole %, or at least 75 mole %, or at least 80 mole %, or at least 85 mole %, or at least 90 mole %, or at least 95 mole %, or at least 98 mole %, or at least 99 mole %. The mole % can represent a bulk composition of the catalyst or a surface composition of the catalyst, such as when the second and third metals are doped on an external surface of the first metal. In embodiments in which the mole% represents a surface composition, the mole % applies to the first two atomic layers of the catalyst composition. In other embodiments, the first metal may be present in the catalyst compositions in an amount of from about 60 mole % to about 99 mole %. In other embodiments, the first metal may be present in the catalyst compositions in an amount of from about 65 mole % to about 99 mole %, or from about 70 mole % to about 99 mole %, or from about 75 mole % to about 99 mole %, or from about 80 mole % to about 99 mole %, or from about 85 mole % to about 99 mole %, or from about 60 mole % to about 95 mole %, or from about 60 mole % to about 90 mole %, or from about 60 mole % to about 85 mole %, or from about 60 mole % to about 80 mole %, or from about 60 mole % to about 75 mole %, or from about 60 mole % to about 70 mole %, or from about 60 mole % to about 65 mole %.

[0044] In certain embodiments, the second metal may be present in the catalyst compositions in an amount of up to 20 mole %, calculated based on the number of moles of the second metal in the catalyst composition divided by the sum of the number of moles of all components in the catalyst composition, such as the number of moles of the first metal, the second metal, and the third metal in the catalyst composition, multiplied by 100%. In other embodiments, the second metal may be present in the catalyst compositions in an amount of up to 18 mole %, or up to 15 mole %, or up to 12 mole %, or up to 10 mole %, or up to 8 mole %, or up to 6 mole %, or up to 5 mole %, or up to 4 mole %. or up to 1 mole %. The mole % can represent a bulk composition of the catalyst or a surface composition of the catalyst, such as when the second and third metals are doped on an external surface of the first metal. In embodiments in which the mole % represents a surface composition, the mole % applies to the first two atomic layers of the catalyst composition. In other embodiments, the second metal may be present in the catalyst compositions in an amount of from about 1 mole % to about 20 mole %. In other embodiments, the second metal may be present in the catalyst compositions in an amount of from about 5 mole % to about 20 mole %, or from about 10 mole % to about 20 mole %, or from about 15 mole % to about 20 mole %, or from about 1 mole % to about 10 mole %. or from about 1 mole % to about 15 mole %, or from about 5 mole % to about 10 mole %, or from about 5 mole % to about 15 mole %, or from about 5 mole % to about 20 mole %, or from about 10 mole % to about 20 mole %, or from about 15 mole % to about 20 mole %, or from about 2 mole % to about 20 mole %, or from about 4 mole % to about 20 mole %.

[0045] In certain embodiments, the third metal may be present in the catalyst compositions in an amount of up to 20 mole %, calculated based on the number of moles of the third metal in the catalyst composition divided by the sum of the number of moles of all components in the catalyst composition, such as the number of moles of the first metal, the second metal, and the third metal in the catalyst composition, multiplied by 100%. hr other embodiments, the third metal may be present in the catalyst compositions in an amount of up to 18 mole %, or up to 15 mole %, or up to 12 mole %, or up to 10 mole %, or up to 8 mole %, or up to 6 mole %, or up to 5 mole %, or up to 4 mole %, or up to 1 mole %. The mole % can represent a bulk composition of the catalyst or a surface composition of the catalyst, such as when the second and third metals are doped on an external surface of the first metal. In embodiments in which the mole % represents a surface composition, the mole % applies to the first two atomic layers of the catalyst composition. In other embodiments, the third metal may be present in the catalyst compositions in an amount of from about 1 mole % to about 20 mole %. In other embodiments, the third metal may be present in the catalyst compositions in an amount of from about 5 mole % to about 20 mole %, or from about 10 mole % to about 20 mole %, or from about 15 mole % to about 20 mole %, or from about 1 mole % to about 10 mole %, or from about 1 mole % to about 15 mole %. or from about 5 mole % to about 10 mole %, or from about 5 mole % to about 15 mole %, or from about 5 mole % to about 20 mole %, or from about 10 mole % to about 20 mole %, or from about 15 mole % to about 20 mole %, or from about 2 mole % to about 20 mole %, or from about 4 mole % to about 20 mole %.

[0046] In certain embodiments, the first metal may be present in the catalyst compositions in an amount of at least 60 wt. %, calculated based on the weight of the first metal in the catalyst composition divided by the total weight of catalyst composition, such as the total weight or sum of the weights of the first metal, the second metal, and the third metal in the catalyst composition, multiplied by 100%. In other embodiments, the first metal may be present in the catalyst compositions in an amount of at least 65 wt. %, or at least 70 wt. %, or at least 75 wt. %, or at least 80 wt. %, or at least 85 wt. %, or at least 90 wt. %, or at least 95 wt. %, or at least 98 wt. %, or at least 99 wt. %. The wt. % can represent a bulk composition of the catalyst or a surface composition of the catalyst, such as when the second and third metals are doped on an external surface of the first metal. In embodiments in which the wt. % represents a surface composition, the wt. % applies to the first two atomic layers of the catalyst composition. In other embodiments, the first metalmay be present in the catalyst compositions in an amount of from about 60 wt. % to about 99.65 wt. %. In other embodiments, the first metal may be present in the catalyst compositions in an amount of from about 65 wt. % to about 99.65 wt. %, or from about 70 wt. % to about 99.65 wt. %, or from about 75 wt. % to about 99.65 wt. %, or from about 80 wt. % to about 99.65 wt. %, or from about 85 wt. % to about 99.65 wt. %, or from about 98.7 wt.% to about 99.65 wt.%, or from about 98 wt.% to about 99.65 wt.%, or from about 97.5 wt.% to about 99.65 wt.%, or from about 96 wt.% to about 99.65 wt.%, or from about 95 wt.% to about 99.65 wt.%, or from about 92 wt.% to about 99.65 wt.%, or from about 90 wt.% to about 99.65 wt.%, or from about 88 wt.% to about 99.65 wt.%, or from about 60 wt. % to about 95 wt. %, or from about 60 wt. % to about 90 wt. %, or from about 60 wt. % to about 85 wt. %, or from about 60 wt. % to about 80 wt. %, or from about 60 wt. % to about 75 wt. %. or from about 60 wt. % to about 70 wt. %, or from about 60 wt. % to about 65 wt. %.

[0047] In certain embodiments, the second metal may be present in the catalyst compositions in an amount of up to 20 wt. %, calculated based on the weight of the second metal in the catalyst composition divided by the total weight of catalyst composition, such as the total weight or sum of the weights of the first metal, the second metal, and the third metal in the catalyst composition, multiplied by 100%. In other embodiments, the second metal may be present in the catalyst compositions in an amount of up to 18 wt. %, or up to 15 wt. %, or up to 12 wt. %, or up to 10 wt. %, or up to 8 wt. %, or up to 6 wt. %, or up to 5 wt. %, or up to 4 wt. %, or up to 1 wt. %, or up to 0.65 wt.%, or up to 0.60 wt.%, or up to 0.58 wt.%, or up to 0.55 wt.%, or up to 0.52 wt.%, or up to 0.50 wt.%. or up to 0.48 wt.%. or up to 0.45 wt.%, or up to 0.40 wt%, or up to 0.35 wt.%, or up to 0.30 wt.%, or up to 0.25 wt.%. The wt. % can represent a bulk composition of the catalyst or a surface composition of the catalyst, such as when the second and third metals are doped on an external surface of the first metal. In embodiments in which the wt. % represents a surface composition, the wt. % applies to the first two atomic layers of the catalyst composition. In other embodiments, the second metal may be present in the catalyst compositions in an amount of from about 0.15 wt. % to about 20 wt. %. In other embodiments, the second metal may be present in the catalyst compositions in an amount of from about 0.15 wt.% to about 0.65 wt.%, or from about 0.15 wt.% to about 1.0 wt.%, or from about 0.15 wt.% to about 5.0 wt.%, or from about 0.15 wt.% to about 7.5 wt.%, or from about 0.15 wt.% to about 10.0 wt.%, or from about 0.15 wt.% to about 10.0 wt.%, or from about 0.15 wt.% to about 12.5 wt.%, or from about 0.15 wt.% to about 15.0wt.%, or from about 0.15 wt.% to about 20.0 wt.%, or from about 0.2 wt.% to about 0.45 wt.%, or from about 0.2 wt.% to about 0.50 wt.%, or from about 0.2 wt.% to about 0.65 wt.%, or from about 5 wt. % to about 20 wt. %, or from about 10 wt. % to about 20 wt. %, or from about 15 wt. % to about 20 wt. %, or from about 1 wt. % to about 10 wt. %, or from about 1 wt. % to about 15 wt. %, or from about 5 wt. % to about 10 wt. %, or from about 5 wt. % to about 15 wt. %, or from about 5 wt. % to about 20 wt. %, or from about 10 wt. % to about 20 wt. %, or from about 15 wt. % to about 20 wt. %, or from about 2 wt. % to about 20 wt. %, or from about 4 wt. % to about 20 wt. %.

[0048] In certain embodiments, the third metal may be present in the catalyst compositions in an amount of up to 20 wt. %, calculated based on the weight of the third metal in the catalyst composition divided by the total weight of catalyst composition, such as the total weight or sum of the weights of the first metal, the second metal, and the third metal in the catalyst composition, multiplied by 100%. In other embodiments, the third metal may be present in the catalyst compositions in an amount of up to 18 wt. %, or up to 15 wt. %, or up to 12 wt. %, or up to 10 wt. %, or up to 8 wt. %, or up to 6 wt. %, or up to 5 wt. %, or up to 4 wt. %, or up to 1 wt. %, or up to 0.65 wt.%, or up to 0.60 wt.%, or up to 0.58 wt.%, or up to 0.55 wt.%, or up to 0.52 wt.%, or up to 0.50 wt.%, or up to 0.48 wt.%, or up to 0.45 wt.%, or up to 0.40 wt%, or up to 0.35 wt.%, or up to 0.30 wt.%, or up to 0.25 wt.%. The wt. % can represent a bulk composition of the catalyst or a surface composition of the catalyst, such as when the second and third metals are doped on an external surface of the first metal. In embodiments in which the wt. % represents a surface composition, the wt. % applies to the first two atomic layers of the catalyst composition. In other embodiments, the third metal may be present in the catalyst compositions in an amount of from about 0.15 wt. % to about 20 wt. %. In other embodiments, the third metal may be present in the catalyst compositions in an amount of from about 0.15 wt.% to about 0.65 wt.%, or from about 0.15 wt.% to about 1.0 wt.%, or from about 0.15 wt.% to about 5.0 wt.%, or from about 0.15 wt.% to about 7.5 wt.%, or from about 0.15 wt.% to about 10.0 wt.%, or from about 0.15 wt.% to about 10.0 wt.%, or from about 0.15 wt.% to about 12.5 wt.%, or from about 0.15 wt.% to about 15.0 wt.%, or from about 0.15 wt.% to about 20.0 wt.%, or from about 0.2 wt.% to about 0.45 wt.%, or from about 0.2 wt.% to about 0.50 wt.%, or from about 0.2 wt.% to about 0.65 wt.%, or from about 5 wt. % to about 20 wt. %, or from about 10 wt. % to about 20 wt. %, or from about 15 wt. % to about 20 wt. %, or from about 1 wt. % to about 10 wt. %, or from about 1 wt. % to about 15 wt.%, or from about 5 wt. % to about 10 wt. %, or from about 5 wt. % to about 15 wt. %, or from about 5 wt. % to about 20 wt. %, or from about 10 wt. % to about 20 wt. %, or from about 15 wt. % to about 20 wt. %, or from about 2 wt. % to about 20 wt. %, or from about 4 wt. % to about 20 wt. %.

[0049] In certain embodiments, the first metal may be present in the catalyst compositions in an amount of at least 49 wt. %, calculated based on the weight of the first metal in the catalyst composition divided by the total weight of catalyst composition, such as the total weight or sum of the weights of the first metal, the second metal, and the third metal in the catalyst composition, multiplied by 100%. In other embodiments, the first metal may be present in the catalyst compositions in an amount of at least 50 wt. %, or at least 51 wt. %, or at least 52 wt. %, or at least 53 wt. %, or at least 54 wt. %, or at least 55 wt. %, or at least 56 wt. %, or at least 58 wt. %, or at least 59 wt. %. The wt. % can represent a bulk composition of the catalyst or a surface composition of the catalyst, such as when the second and third metals are doped on an external surface of the first metal. In embodiments in which the wt. % represents a surface composition, the wt. % applies to the first two atomic layers of the catalyst composition. In other embodiments, the first metal may be present in the catalyst compositions in an amount of from about 49 wt. % to about 99 wt. %. In other embodiments, the first metal may be present in the catalyst compositions in an amount of from about 50 wt. % to about 99 wt. %, or from about 52 wt. % to about 99 wt. %, or from about 55 wt. % to about 99 wt. %, or from about 56 wt. % to about 99 wt. %, or from about 58 wt. % to about 99 wt. %, or from about 49 wt. % to about 95 wt. %, or from about 49 wt. % to about 90 wt. %, or from about 49 wt. % to about 85 wt. %. or from about 49 wt. % to about 80 wt. %, or from about 49 wt. % to about 75 wt. %, or from about 49 wt. % to about 70 wt. %, or from about 49 wt. % to about 65 wt. %.

[0050] In certain embodiments, the second metal may be present in the catalyst compositions in an amount of up to 23 wt. %, calculated based on the weight of the second metal in the catalyst composition divided by the total weight of catalyst composition, such as the total weight or sum of the weights of the first metal, the second metal, and the third metal in the catalyst composition, multiplied by 100%. In other embodiments, the second metal may be present in the catalyst compositions in an amount of up to 22 wt. %, or up to 18 wt. %, or up to 12 wt. %, or up to 10 wt. %, or up to 8 wt. %, or up to 6 wt. %, or up to 5 wt. %, or up to 4 wt. %, or up to 1 wt. %. The wt.% can represent a bulk composition of the catalyst or a surface composition of the catalyst, such as when the second and third metals are doped on an external surface of the first metal. In embodiments in which the wt. % represents a surface composition, the wt. % applies to the first two atomic layers of the catalyst composition. In other embodiments, the second metal may be present in the catalyst compositions in an amount of from about 1 wt. % to about 23 wt. %. In other embodiments, the second metal may be present in the catalyst compositions in an amount of from about 5 wt. % to about 23 wt. %, or from about 10 wt. % to about 23 wt. %, or from about 15 wt. % to about 23 wt. %, or from about 1 wt. % to about 10 wt. %. or from about 1 wt. % to about 15 wt. %, or from about 5 wt. % to about 10 wt. %, or from about 5 wt. % to about 15 wt. %, or from about 5 wt. % to about 23 wt. %, or from about 10 wt. % to about 23 wt. %, or from about 15 wt. % to about 23 wt. %, or from about 2 wt. % to about 23 wt. %. or from about 4 wt. % to about 23 wt. %.

[0051] In certain embodiments, the third metal may be present in the catalyst compositions in an amount of up to 28 wt. %, calculated based on the weight of the third metal in the catalyst composition divided by the total weight of catalyst composition, such as the total weight or sum of the weights of the first metal, the second metal, and the third metal in the catalyst composition, multiplied by 100%. In other embodiments, the third metal may be present in the catalyst compositions in an amount of up to 26 wt. %, or up to 25 wt. %, or up to 24 wt. %, or up to 22 wt. %, or up to 8 wt. %, or up to 6 wt. %, or up to 5 wt. %, or up to 4 wt. %, or up to 1 wt. %. The wt. % can represent a bulk composition of the catalyst or a surface composition of the catalyst, such as when the second and third metals are doped on an external surface of the first metal. In embodiments in which the wt. % represents a surface composition, the wt. % applies to the first two atomic layers of the catalyst composition. In other embodiments, the third metal may be present in the catalyst compositions in an amount of from about 1 wt. % to about 28 wt. %. In other embodiments, the third metal may be present in the catalyst compositions in an amount of from about 5 wt. % to about 28 wt. %. or from about 10 wt. % to about 28 wt. %, or from about 15 wt. % to about 28 wt. %, or from about 1 wt. % to about 10 wt. %, or from about 1 wt. % to about 15 wt. %, or from about 5 wt. % to about 10 wt. %, or from about 5 wt. % to about 15 wt. %, or from about 5 wt. % to about 28 wt. %, or from about 10 wt. % to about 28 wt. %, or from about 15 wt. % to about 28 wt. %, or from about 2 wt. % to about 28 wt. %, or from about 4 wt. % to about 28 wt. %.

[0052] In certain embodiments, the catalyst compositions may be in the form of particles having a size range and / or an average size range of from about 10 nm to about 1000 nm. In other embodiments, the catalyst compositions may be in the form of particles characterized by an average diameter of up to 10 nm, or up to 20 nm, or up to 50 nm, or up to 100 nm, or up to 200 nm, or up to 500 nm, or up to 1000 nm. In other embodiments, the catalyst compositions may be in the form of particles characterized by an average diameter of from about 10 nm to about 1000 nm, or from about 50 nm to about 1000 nm, or from about 100 nm to about 1000 nm, or from about 250 nm to about 1000 nm, or from about 500 nm to about 1000 nm, or from about 750 nm to about 1000 nm, or from about 10 nm to about 250 nm, or from about 100 nm to about 250 nm, or from about 150 nm to about 350 nm, or from about 250 nm to about 500 nm.

[0053] In certain embodiments, the catalyst composition is characterized by a total current density of at least 75 mA / cm2and a Faradaic efficiency (FE) of at least 55% at -1.1 V vs. RHE toward the production of liquid C2+ oxygenates. In certain embodiments, the catalyst compositions may be characterized by a FE of at least 60%, or at least 62%, or at least 65%, or at least 68%, or at least 70%. or at least 72%, or at least 75% at -1.1 V vs. RHE toward the production of liquid C2+ oxygenates. In certain embodiments, the catalyst compositions may be characterized by a total current density of at least 80 mA / cm2, or at least 85 mA / cm2, or at least 90 mA / cm2, or at least 95 mA / cm2, or at least 100 mA / cm2. or at least 105 mA / cm2, or at least 110 mA / cm2, or at least 115 mA / cm2, or at least 120 mA / cm2, or at least 125 mA / cm2, or at least 130 mA / cm2, or at least 135 mA / cm2, or at least 140 mA / cm2, or at least 145 mA / cm2, or at least 150 mA / cm2, or at least 155 mA / cm2, or at least 160 mA / cm2, or at least 170 mA / cm2, or at least 175 mA / cm2at -1.1 V.

[0054] In certain embodiments of the catalyst composition (e.g., catalyst compositions 100, 200), the first metal is copper (Cu), the second metal is yttrium (Y), and the third metal is palladium (Pd). In certain embodiments, the catalyst composition is a YiPdiCu dual-atom catalyst (DAC) that is substantially free from components other than the first metal, the second metal, and the third metal. In certain embodiments, the ratio of Y to Cu is from about 1:4 to about 1:1000 on a molar basis or a weight basis, and the ratio of Pd to Cu is from about 1 :4 to about 1 : 1000 on a molar basis or a weight basis.

[0055] In certain embodiments, the catalyst compositions are characterized by a current density of up to about 175 mA / cm2and a Faradaic efficiency towards ethanol of up to about 75%. Other known catalysts have much lower current densities, with the highest being in a range of about 15-35 mA / cm2. Few known catalysts exhibit a Faradaic efficiency towards ethanol that exceeds 40%.

[0056] According to another aspect of the present disclosure, methods for the electrochemical reduction of carbon dioxide are provided. The methods may include, for example, electrochemically reducing a reaction mixture comprising carbon dioxide in the presence of any of the presently disclosed catalyst compositions. In certain embodiments, the reaction mixture may be a waste stream or other carbon dioxide-containing stream derived from one or more industrial processes, particularly industrial processes that produce significant amounts of carbon dioxide, or a carbon dioxide-containing stream that is otherwise in need of carbon dioxide reduction or mitigation.

[0057] In general, the methods are operable to generate a product stream comprising one or more C2+ organic compounds. The one or more C2+ organic compounds may, for example, be selected from the group consisting of ethanol, ethylene, acetic acid, acetate, and any combination thereof. In other embodiments, the product stream produced by the methods may be a liquid product stream comprising one or more C2+ oxygenate compounds. The one or more C2+ oxygenate compounds may, for example, be selected from the group consisting of ethanol, acetic acid, acetate, and any combination thereof. In certain embodiments, the liquid product stream may comprise at least 70% by weight ethanol. In other embodiments, the liquid product stream may comprise at least 75% by weight ethanol, or at least 80% by weight ethanol, or at least 85% by weight ethanol, or at least 90% by weight ethanol, or at least 95% by weight ethanol, or at least 98% by weight ethanol, or at least 98.5% by weight ethanol, or at least 99% by weight ethanol. In certain embodiments, the liquid product stream may contain less than 2% by weight propanol, or less than 1.5% by weight propanol, or less than 1% by weight propanol.

[0058] In certain embodiments, the methods are characterized by a catalyst Faradaic efficiency (FE) of at least 55% at -1.1 V vs. RHE toward the production of the liquid product stream. In other embodiments, the methods are characterized by a catalyst Faradaic efficiency (FE) of at least 60%, or at least 62%, or at least 65%, or at least 68%, or at least 70%, or at least 72%, or at least75% at -1.1 V vs. RHE toward the production of the liquid product stream, (e.g., liquid C2+ oxygenates).

[0059] In certain embodiments, the method for the electrochemical reduction of carbon dioxide may also include supplying a reaction mixture stream comprising carbon dioxide (CO2) to a CO2 electrolyzer or an electrochemical cell configured to electrochemically reduce CO2. The method may also include causing the electrochemical reduction of CO2 in the reaction mixture stream by the provision of voltage to the electrodes and recovering a liquid product stream from the CO2 electrolyzer cell. The liquid product stream may include, for example, one or more C2+ oxygenate compounds selected from the group consisting of ethanol, acetic acid, acetate, and any combination thereof.

[0060] The CO2 electrolyzer or electrochemical cell used in the methods may be any CO2 electrolyzer or electrochemical cell operable to electrochemically reduce CO2. FIG. 3 illustrates an exemplary embodiment of a CO2 electrolyzer system 300 and electrochemical cell 350 that may be used with the methods. Other CO2 electrolyzers and electrochemical cells may also be used with the methods. As shown in FIG. 3, CO? electrolyzer system 300 and electrochemical cell 350 may include a working electrode 305 or cathode 305 disposed in cathode chamber 385 and a counter electrode 310 or anode 310 disposed in anode chamber 380. As shown in FIG. 3, the working electrode 305 or cathode 305 may comprise or otherwise be coated with any of the presently disclosed catalyst compositions (e.g., catalyst compositions 100, 200). The working electrode or cathode 305 is the site of the CO2 reduction reaction (CO2RR) and where CO2 receives electrons and is converted into valuable chemical feedstocks, such as C2+ organic compounds. The counter electrode or anode 310 is the site of the oxidation reaction, typically involving the oxidation of water to produce oxygen gas which may be vented from the anode chamber 380 as oxygen gas stream 365.

[0061] In certain embodiments, CO2 electrolyzer system 300 and electrochemical cell 350 may also include a reference electrode 315 disposed in the cathode chamber 385. Reference electrode 315 may be a stable electrode with a known potential (e.g., Ag / AgCl or saturated calomel electrode) that is used to measure and control the potential of the working electrode or cathode 305. CO2 electrolyzer 300 and electrochemical cell 350 may or may not include an electrolyte 375in the form of an ionic solution that at least partially fills electrochemical cell 350, particularly cathode chamber 385 and anode chamber 380. When present, electrolyte 375 conducts ions between the working electrode or cathode 305 in cathode chamber 385 and counter electrode or anode 310 in anode chamber 380. CO2 electrolyzer system 300 and electrochemical cell 350 may also include an ion exchange membrane 320 configured to prevent the mixing of products between the cathode and anode chambers while still allowing ions to pass through to complete the electrical circuit.

[0062] As shown in FIG. 3, reaction mixture stream 302 comprising carbon dioxide (CO2) may be supplied to CO2 electrolyzer 300 and electrochemical cell 350 such that reaction mixture stream 302 is supplied to cathode chamber 385 where it may react with catalyst 100, 200 at the working electrode or cathode 305. In certain embodiments, reaction mixture stream 302 may be bubbled into the catholyte or electrolyte 375 in cathode chamber 385. The electrochemical reduction of CO2 in the reaction mixture stream in the presence of catalyst composition 100, 200 may be caused by the provision of voltage to electrodes 305, 310. Liquid product stream 325 and gaseous product stream 330 generated by the electrochemical reduction of CO2 in CO2 electrolyzer system 300 and electrochemical cell 350 may be recovered from cathode chamber 385, as shown in FIG. 3.

[0063] FIG. 4 is an illustrative diagram of a method 400 for the electrochemical reduction of carbon dioxide. As shown in FIG. 4, method 400 may optionally include, at block 402 supplying a reaction mixture stream comprising CO2 to a CO2 electrolyzer system or electrochemical cell configured to electrochemically reduce CO2. The CO2 electrolyzer system or electrochemical cell may include at least a counter electrode or anode as well as a working electrode or cathode comprising, or coated with, any of the presently disclosed catalyst compositions. At block 404, method 400 may further include electrochemically reducing the reaction mixture comprising CO2 in the presence of any of the presently disclosed catalyst compositions to generate a product stream comprising one or more C2+ organic compounds. Method 400 may also optionally include, at block 406, providing voltage to the electrodes of the electrolyzer system or electrochemical cell so as to cause the electrochemical reduction of the CO2 in the reaction mixture stream. At block 408, method 400 may also optionally include recovering the product stream from the electrolyzer system or electrochemical cell. The product stream may include, for example, one or more C2+ organic compounds.

[0064] According to another aspect of the present disclosure, methods of preparing the catalyst compositions are provided. In certain embodiments, the catalyst compositions may be prepared by: (1) combining a second metal solution and a third metal solution with a liquid dispersion of a first metal catalyst matrix precursor to generate a liquid solution that contains a catalyst precursor solid; (2) isolating the catalyst precursor solid from the liquid solution; (3) annealing the catalyst precursor solid to produce a substantially impurity-free catalyst precursor; and (4) reducing, electrochemically, the catalyst precursor to produce the catalyst composition.

[0065] In other embodiments, the catalyst compositions may be prepared by: (1) generating a first metal catalyst precursor matrix by precipitation from a first metal chloride and NaOH solution; (2) combining a third metal chloride solution with a liquid dispersion of the first metal catalyst matrix precursor to generate a first liquid solution that contains an intermediate catalyst precursor solid; (3) combining a second metal nitrate solution with the first liquid solution to produce a second liquid solution that contains a catalyst precursor solid; (4) isolating the catalyst precursor solid from the liquid solution; (5) annealing the catalyst precursor solid to produce a substantially impurity-free catalyst precursor; and (6) reducing, electrochemically, the catalyst precursor to produce the catalyst composition. In certain embodiments, generating the first metal catalyst precursor matrix may include causing the precipitation of a first metal catalyst precursor matrix through the simultaneous dropwise addition of 0.5M first metal chloride solution and 0.5M NaOH solutions into deionized water under a continuous N2 atmosphere with constant stirring at a pH of about 9.5.

[0066] In other embodiments, a method of preparing a YiPdiCu catalyst composition for the electrochemical reduction of carbon dioxide is provided. The method may include: (1) combining a PdCb solution and a Y(NO3)s-6H2O solution with a liquid dispersion of a Cu(OH)2 catalyst matrix precursor to generate a liquid solution that contains a catalyst precursor solid; (2) isolating the catalyst precursor solid from the liquid solution; (3) annealing the catalyst precursor solid to produce a substantially impurity-free YPdCuO catalyst precursor; and (4) reducing, electrochemically, the YPdCuO catalyst precursor to produce the Y iPdiCu catalyst composition.

[0067] FIG. 5 is an illustrative diagram of an exemplary method 500 for preparing a YiPdiCu catalyst composition for the electrochemical reduction of carbon dioxide. As shown in FIG. 5,method 500 may include, at block 502, generating a Cu(OH)2 catalyst precursor matrix by precipitation from a CuQ2-2H2O and NaOH solution. At block 504, method 500 may further include combining a PdCb solution with a liquid dispersion of a Cu(OH)2catalyst matrix precursor to generate a first liquid solution that contains an intermediate catalyst precursor solid. Method 500 may further include, at block 506, combining a Y(NO3)3-6H2O solution with the first liquid solution to produce a second liquid solution that contains a catalyst precursor solid. At block 508, method 500 may further include isolating the catalyst precursor solid from the liquid solution. Method 500 may further include, at block 510, annealing the catalyst precursor solid to produce a substantially impurity-free YPdCuO catalyst precursor. At block 512, method 500 may further include electrochemically reducing the YPdCuO catalyst precursor to produce the YiPdiCu catalyst composition. In certain embodiments, generating the Cu(OH)2 catalyst precursor matrix at block 502 may include causing the precipitation of a Cu(OH)2 catalyst precursor matrix through the simultaneous dropwise addition of 0.5M CuQ2-2H2O and 0.5M NaOH solutions into deionized water under a continuous N2 atmosphere with constant stirring at a pH of about 9.5. It will be recognized by the person of skill in the art that the steps at blocks 504 and 506 may be reversed in certain embodiments of method 500.EXAMPLES

[0068] Various examples are described to illustrate selected aspects of the various embodiments of catalyst compositions, systems, and methods for the electrochemical reduction of carbon dioxide.Example 1 - Preparation of Catalyst Composition

[0069] A YiPdiCu dual-atom doped catalyst was synthesized via a two-step process that included a precipitation first step and a cation-exchange second step. In the first step, a CLI(OH)2 catalyst precursor composition was prepared by simultaneously adding 0.5M CUC12-2H2O and 0.5M NaOH solutions dropwise into 90 mL of deionized water under a continuous N2atmosphere with constant stirring. The pH of the reaction medium was maintained at approximately 9.5 throughout the precipitation process. After aging the suspension for 8 h at room temperature under stirring, the resulting blue slurry was washed and centrifuged several times with deionized wateruntil the supernatant reached a neutral pH (~7). The collected precipitate was then dried under vacuum for 12 h (overnight) to obtain a Cu(0H)2 matrix.

[0070] In the second step, cation exchange was carried out by injecting a 1 mg / mL PdCE solution into a 10 mg / mL dispersion of the Cu(OH)2 matrix, followed by stirring for 2.5 h. Subsequently, a 1 mg / mL solution of Y(NO3)3-6H2O was added to the mixture and stirred for an additional 2.5 h. The resulting product was washed and centrifuged using a 1:1 (v / v) ethanol¬ deionized water mixture, then dried under vacuum for 12 h. The obtained solid was annealed at 330°C for 3 h in air to yield an impurity-free YPdCuO precursor.

[0071] Finally, the YiPdiCu alloy catalyst was generated via in-situ electrochemical reduction of YPdCuO at -0.6 V versus the reversible hydrogen electrode (RHE) in 0.5 M KHCO3 electrolyte. A platinum (Pt) foil and a saturated Ag / AgCl electrode served as the counter and reference electrodes, respectively, while the YPdCuO-coated gas diffusion layer (GDL) was used as the working electrode. The final prepared Y iPdiCu alloy catalyst comprised 99.34 wt.% Copper (Cu), 0.23 wt.% Yttrium (Y), and 0.43 wt.% Palladium (Pd). FIG.6 is an Attenuated Total Reflectance Surface-Enhanced Infrared Absorption Spectroscopy (ATR-SEIRAS) data plot of wavenumber (cm1) versus absorbance [a.u.] for the YiPdiCu catalyst composition. As shown in FIG. 6, obvious peaks for key reaction intermediates in the electrochemical reduction of carbon dioxide are demonstrated for the YiPdiCu catalyst composition.

[0072] FIG. 10 is an in situ X-ray absorption near edge structure (XANES) data plot showing Photon energy [eV] versus Normalized absorption [a.u.] for the prepared YiPdiCu catalyst composition. As shown in FIG. 10, the in situ XANES data plots demonstrate that Cu is completely reduced from CuO to metallic Cu for the YiPdiCu catalyst composition. FIG. 11 is an in situ extended X-ray absorption fine structure (EXAFS) data plot showing R [A] versus FT [k (k)] for the prepared YiPdiCu catalyst composition. FIG. 11 also demonstrates that Cu is completely reduced from CuO to metallic Cu in the YiPdiCu catalyst composition. FIG. 12 is an in situ EXAFS data plot showing R [A] versus FT [k (k)] for the prepared Y iPdiCu catalyst composition in comparison to a PdiCu catalyst and Pd foil. FIG. 12 confirms that Pd exists as a single atom species in the prepared YiPdiCu catalyst. FIG. 12 further demonstrates that while Pd exists in a metallic state in PdiCu (due to the metallic nature of the Cu matrix), Pd in YiPdiCu ispartially cationic due to the influence of nearby YiOxspecies. FIG. 13A and FIG. 13B are in situ EXAFS data plots showing R [A] versus FT [k3 / (k)] for the prepared YiPdiCu catalyst composition (FIG. 13A) and for a YiCu catalyst (FIG. 13B), respectively. FIG. 13A and FIG.13B confirm that Y exists as a single atom YOXspecies in the prepared YiPdiCu catalyst.Example 2 - Use of the Catalyst Composition for the Electrochemical Reduction of CO2

[0073] Performance tests were earned out under CO2 reduction (CO2R) conditions using a three-electrode system, with platinum (Pt) foil as the counter electrode, saturated Ag / AgCl as the reference electrode, and the designed Y iPdiCu dual atom catalyst (DAC) composition prepared in Example 1 as the working electrode. As shown in FIG. 7 and FIG. 8, the experimental results indicate that at -1.1 V vs. RHE, the YiPdiCu catalyst achieved a total current density of 172 mA / cm2and a 72.2% Faradaic efficiency (FE) towards ethanol. The current density (J) represents catalyst activity while FE represents catalyst selectivity. This performance significantly surpassed that of the parent Cu catalyst which exhibits a current density of 73 mA / cm2and an FE of 13.2%, as well as the single atom alloy counterparts: PdiCu (60 mA / cm2, 50.5%) and YiCu (55 mA / cm2, 38.4%). These results not only exceed the benchmark CO2 reduction catalyst (Cu) but also distinguish YiPdiCu as a leading electrocatalyst for the electrochemical reduction of CO2 to liquid C2+ oxygenates, particularly ethanol. The generated liquid product stream obtained from the electrochemical cell was comprised of 99.16 wt.% ethanol and 0.7% propanol.

[0074] In particular, it was discovered that Y-doping promotes CO2 activation and CO formation whereas Pd inhibits the desorption of CO but promotes C-C coupling for C2+ product formation. The weak oxophilicity of Pd relative to Cu preserves oxygen intermediates thereby promoting liquid products over ethylene. The improved performance of the YiPdiCu catalyst composition prepared in Example 1 demonstrates the importance of the synergistic interaction in the dual-atom alloy composition. FIG.9 confirms the synergistic interaction in the dual-atom alloy composition by demonstrating that the FE performance of the YiPdiCu catalyst composition shown in FIG. 8 is greater than the additive performance of the YiCu and PdiCu single atom alloy compositions.

[0075] Other objects, features and advantages of the disclosure will become apparent from the foregoing figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of thedisclosure, are given by way of illustration only and are not meant to be limiting. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.

Claims

ClaimsWhat is claimed is:

1. A catalyst composition for the electrochemical reduction of carbon dioxide, the catalyst composition comprising:a first metal selected from the group consisting of copper (Cu). gold (Au), silver (Ag), and any combination, alloy, or mixture thereof;a second metal selected from the group consisting of yttrium (Y), scandium (Sc), titanium (Ti), zirconium (Zr), hafnium (Hf), and any combination, alloy, or mixture thereof; and a third metal selected from the group consisting of palladium (Pd), platinum (Pt), and any combination, alloy, or mixture thereof.

2. The catalyst composition according to claim 1, wherein each of the second metal and the third metal is doped onto an external surface of the first metal.

3. The catalyst composition according to claim 1, wherein single atoms of the second metal and single atoms of the third metal are dispersed on an external surface of the first metal.

4. The catalyst composition according to claim 3, further comprising a metal support structure, the metal support structure comprising the first metal.

5. The catalyst composition according to claim 1, wherein the catalyst composition comprises a dual-atom catalyst (DAC), wherein the DAC comprises single atoms of the second and third metals doped into a base metal matrix to form a trimetallic alloy, and wherein the base metal matrix comprises the first metal.

6. The catalyst composition according to claim 5, wherein the single atoms of the second and third metals are distributed throughout the base metal matrix so as to define distributed second and third metals such that the distributed second and third metals are either: (a) directly bonded to one another, or (b) in close enough proximity to one another to be bonded to each otherthrough an adsorbing or bridging species, the adsorbing or bridging species selected from oxygen, carbon monoxide, carbon dioxide, and formate, singly or in any combination.

7. The catalyst composition according to claim 1, wherein the catalyst comprises a dual-atom catalyst (DAC), wherein the DAC comprises single atoms of the second and third metals dispersed on an external surface of the first metal, wherein the single atoms of the second and third metals are positioned on the surface of the first metal such that they are either: (a) directly bonded to one another, or (b) in close enough proximity to one another to be bonded through an adsorbing or bridging species, the adsorbing or bridging species selected from oxygen, carbon monoxide, carbon dioxide, and formate, singly or in any combination.

8. The catalyst composition according to claim 1, wherein:the catalyst composition is substantially free from components other than the first metal, the second metal, and the third metal;the ratio of the second metal to the first metal is from about 1:4 to about 1:1000 on a molar basis or a weight basis; andthe ratio of the third metal to the first metal is from about 1:4 to about 1:1000 on a molar basis or a weight basis.

9. The catalyst composition according to claim 1, further comprising:at least 60% by weight of the first metal;up to 20% by weight of the second metal; andup to 20% by weight of the third metal.

10. The catalyst composition according to claim 1, wherein:the first metal comprises copper (Cu);the second metal comprises yttrium (Y); andthe third metal comprises palladium (Pd).

11. The catalyst composition according to claim 10, wherein the catalyst composition comprises a YiPdiCu dual-atom catalyst (DAC) substantially free from components other than the firstmetal, the second metal, and the third metal, wherein the ratio of Y to Cu is from about 1:4 to about 1 : 1000 on a molar basis or a weight basis, and wherein the ratio of Pd to Cu is from about 1:4 to about 1:1000 on a molar basis or a weight basis.

12. The catalyst composition according to claim 1, wherein the catalyst composition has a total current density of at least 150 mA / cm2and a Faradaic efficiency (FE) of at least 65% at -1.1 V vs. RHE toward the production of liquid C2+ oxygenates.

13. A method for the electrochemical reduction of carbon dioxide, the method comprising:reducing, electrochemically, a reaction mixture in the presence of a catalyst composition according to claim 1 to generate a product stream, the reaction mixture comprising carbon dioxide and the product stream comprising one or more C2+ organic compounds.

14. The method according to claim 13, wherein the product stream comprises a liquid product stream, the liquid product stream comprising one or more C2+ oxygenate compounds selected from the group consisting of ethanol, acetic acid, acetate, and any combination thereof.

15. The method according to claim 14, wherein the liquid product stream further comprises at least 95% by weight ethanol.

16. The method according to claim 13, further comprising:producing a liquid product stream, the liquid product stream comprising one or more C2+ oxygenate compounds selected from the group consisting of ethanol, acetic acid, acetate, and any combination thereof, the method having a catalyst Faradaic efficiency (FE) of at least 65% at -1.1 V vs. RHE toward the production of the liquid product stream.

17. The method according to claim 13, further comprising:supplying a reaction mixture stream comprising carbon dioxide (CO2) to a CO2 electrolyzer cell configured to electrochemically reduce CO2, the CO2 electrolyzer cell comprising a working electrode or cathode and a counter electrode or anode, the working electrode or cathode comprising, or coated with, a catalyst composition according to claim 1;causing the electrochemical reduction of CO2 in the reaction mixture stream by the provision of voltage to the electrodes; andrecovering a liquid product stream from the CO2 electrolyzer cell, the liquid product stream comprising one or more C2+ oxygenate compounds selected from the group consisting of ethanol, acetic acid, acetate, and any combination thereof.

18. A method of preparing a YiPdiCu catalyst composition for the electrochemical reduction of carbon dioxide, the method comprising:combining a PdCT solution and a Y(NOs)3-6H2O solution with a liquid dispersion of a CU(OH)2catalyst matrix precursor to generate a liquid solution that contains a catalyst precursor solid;isolating the catalyst precursor solid from the liquid solution;annealing the catalyst precursor solid to produce a substantially impurity-free YPdCuO catalyst precursor; andreducing, electrochemically, the YPdCuO catalyst precursor to produce the YiPdiCu catalyst composition.

19. The method according to claim 18, further comprising:generating a Cu(OH>2 catalyst precursor matrix by precipitation from a CuQ2-2H2O and NaOH solution;combining a PdCl2solution with a liquid dispersion of a CU(0H)2catalyst matrix precursor to generate a first liquid solution that contains an intermediate catalyst precursor solid;combining a Y(NO3)3-6H2O solution with the first liquid solution to produce a second liquid solution that contains a catalyst precursor solid;isolating the catalyst precursor solid from the liquid solution;annealing the catalyst precursor solid to produce a substantially impurity-free YPdCuO catalyst precursor; andreducing, electrochemically, the YPdCuO catalyst precursor to produce the YiPdiCu catalyst composition.

20. A system for the electrochemical reduction of carbon dioxide, the system comprising:a CO2 electrolyzer cell comprising a working electrode or cathode and a counter electrode or anode, the working electrode or cathode comprising, or coated with, a catalyst composition according to claim 1;wherein the CO2 electrolyzer cell is configured to receive a reaction mixture stream comprising carbon dioxide (CO2) and electrochemically reduce CO2 upon the provision of voltage to the electrodes to produce a liquid product stream comprising one or more C2+ oxygenate compounds selected from the group consisting of ethanol, acetic acid, acetate, and any combination thereof.

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