Lewis / Brønsted acid / base and nickel phosphide binary catalyst system (co-catalyst) for direct electrochemical reduction of CO2 into hydrocarbons

Abstract

A cathode is disclosed that includes a conductive support substrate having an electrocatalytic coating containing nickel phosphide nanoparticles and a promoter. The conductive support substrate can incorporate a material to be reduced, such as CO or CO. The promoter is either incorporated in the electrolyte solution, in the conductive support, or adsorbed, deposited, or incorporated into the bulk cathode material, and alters the electrocatalytic properties by interacting with reaction intermediates to enhance carbon product selectivity. An electrochemical method for selectively producing hydrocarbon and / or carbohydrate products from CO or CO using water as a hydrogen source is also disclosed.

Description

[Technical Field]

[0001] Cross-reference of related applications This application claims priority to U.S. Nonprovisional Patent Application No. 16 / 878,165, filed on 19 May 2020, which is a continuation-in-part (CIP) of U.S. Patent Application No. 15 / 765,896, filed on 4 April 2018, and to U.S. Provisional Patent Application No. 62 / 239,389, filed on 9 October 2015, under Section 119(e) of the U.S. Patent Act. All of the above disclosures are incorporated herein by reference in their entirety.

[0002] The present invention relates to a novel binary catalyst system combining an acid / base co-catalyst and a nickel phosphide electrocatalyst for the direct electrochemical reduction of carbon dioxide and / or carbon monoxide and / or α-hydrogen-reactive aldehydes and ketones into hydrocarbons, carbohydrates and other useful products collectively referred to below as oxygenated hydrocarbons (or oxyhydrocarbons). [Background technology]

[0003] Conventional fossil resources are being depleted by human activity, and carbon dioxide is increasing in the atmosphere. This is the greatest challenge of the current generation: to stop the creation of uninhabitable planets. A crucial part of this challenge is to provide a commercially viable example of sustainable chemical manufacturing where waste is fully recycled and fossil energy is replaced by renewable energy. This application centers on these objectives. The inherently intermittent nature of most renewable energy sources (e.g., solar and wind) necessitates the need for energy storage. A safe way to store large amounts of energy is through chemical bonding. Chemical bonding is also essential for producing bulk chemicals (supply materials) used to manufacture more complex materials. The chemical industry currently relies on chemical transformation to produce these materials from petroleum, natural gas, and coal (fossil resources). Fossil resource complexes and variable mixtures of chemical compounds. The future renewable economy has not yet learned how to replicate these products. The production of complex chemicals directly from CO2 and water is one such possible solution for both energy storage and a sustainable chemical industry that can close the carbon loop. The recent availability of large natural gas resources in the United States has led to increased large-scale investment in industries that rely on inexpensive natural gas. The relatively clean flow of waste CO2 generated from the combustion of natural gas by these industries can be utilized as a resource for recycling for both energy storage and chemical supply raw material production. This application provides a direct method for achieving this recycling.

[0004] The electrochemical reduction of CO2 (direct CO2 reduction reaction, DCRR) requires a hydrogen source (H + / e - Hydrogenation is carried out using water as the catalyst to produce alkanes on Cu, and alcohols on noble metals and copper oxide. These techniques cannot have a significant impact due to these limitations, and furthermore, in water, competition with H2 production (by-product) is significant, the cost of noble metal electrocatalysts is high, and when abundant Cu is used as the electrocatalyst, the product selectivity is insufficient, making it impossible to produce a single alkane or alkene product. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Therefore, there is a strong demand for selective, cheaper, and more energy-efficient DCRR catalysts to produce various useful carbon-based products such as fuels, chemicals, and plastics from carbon dioxide. [Means for solving the problem]

[0006] The present invention provides a more efficient and improved two-component catalyst system and method for performing DCRR.

[0007] In this disclosure, all surface-bonded intermediates are indicated by an asterisk (*). Based on the identified problems of competition between hydrogen evolution and DCRR described above, it might seem intuitive to propose using a minimally active H2-evolving electrocatalyst (e.g., SnO2) for DCRR. However, the reduction of CO2 and CO to hydrogenation products requires an electrocatalyst that forms surface-bonded hydrogen species (*H). Such hydrogen species may have different partial charges, and the hydrides (*H) δ- ), atomic hydrogen (*H), and / or partially reduced protons (*H) δ+ ) include, where δ is 0 to 1. These are collectively referred to herein as hydrides. These are the same precursors required to produce H2 in water. Therefore, understanding and controlling the types of surface hydrides and their relative reactivity with water vs. CO2 / CO and DCRR reaction intermediates is a crucial factor in achieving selective DCRR electrocatalysis. A previously disclosed electrocatalyst based on a transition metal phosphide for the electroreduction of CO2 to hydrocarbons (U.S. Patent Application No. 15 / 765,896) demonstrates how selectivity between H2 and CO2 / CO can be controlled using such a binary compound as the sole electrocatalyst.

[0008] It is hereby discovered that adding a different class of catalyst (referred to herein as co-catalyst) to a previously disclosed electrocatalyst (based on a transition metal phosphide for the electrochemical reduction of CO2 to hydrocarbons; U.S. Patent Application No. 15 / 765,896) improves specific product selectivity and forms carbon products containing one or more carbon atoms. When used together, the joint electrocatalyst + co-catalyst is referred to as a catalytic system. These act on carbon dioxide and / or carbon monoxide, as well as the following additives and intermediates: hydrocarbons, aldehydes, or ketones. The co-catalyst currently claimed encompasses all possible additives to nickel-phosphorus binary compounds that modify the performance of the catalytic process without being consumed by themselves. The additive may contain any element or compound other than nickel-phosphorus binary compounds (i.e., nickel phosphide) in amounts less than 50% by weight of the composition.

[0009] This co-catalyst binds to the reaction intermediate either in solution or on the surface, and by increasing selectivity for the product, 1) influences the bond orientation and bond strength of the intermediate, thereby 2) activating the intermediate for subsequent reactions with surface-bonded hydrides or other CO2 / CO or other Cn reaction intermediates, thereby 3) promoting the formation of new reaction intermediates on the surface, or thereby 4) leading to the desorption of the reaction intermediate.

[0010] The combination of a co-catalyst and a transition metal phosphide catalyst alters the carbon product selectivity with only a slight effect on the H2-to-DCRR selectivity. For example, the catalyst system alters the distribution among carbon products of the following chemical classes: hydrocarbons, carboxylic acids, aldehydes, ketones, ethers, and alcohols (either aromatic or aliphatic). The co-catalyst can act on the reaction intermediates or electrocatalyst (catalytic system) as described above to achieve this overall result without requiring separate steps or reactors. The co-catalyst can act either directly by binding to the electrocatalyst (so-called "push effect") or directly by binding to one of the reaction intermediates bound to its surface (so-called "pull effect"). Alternatively, the co-catalyst can act indirectly in solution to modify the concentrations of reactants or products to affect their respective availability for activation by the electrocatalyst (transition metal phosphide). In the latter case, these intermediates may or may not be formed on the electrocatalyst alone. The co-catalyst can be immobilized on the electrocatalyst in a subsequent synthesis step, directly incorporated during electrocatalyst synthesis, incorporated into a support, or dissolved in the electrolyte solution together with the reactants.

[0011] The improved product selectivity provided by such catalytic systems enables electrochemical methods for producing purer compounds with less processing required. For example, ethylene glycol can be produced from CO2, water, and renewable electricity, making it possible to produce environmentally friendly and sustainable polymers for various markets. Ethylene glycol and related diols are commercially used as monomers in polymer production. Similarly, various other feedstocks and monomers, such as C3 compounds, methylglyoxal (1,2-propanedione; MEG), and C5 compound mixtures of 3-hydroxy-2-furancarboxaldehyde and 2-hydroxy-3-furancarboxaldehyde, can be produced from CO2, and this mixture has potential utility, among other things, as an octane booster in fuel.

[0012] One aspect of the present invention is a cathode for the direct electrochemical reduction of carbon dioxide and / or carbon monoxide that: 1) includes / does not include a carbohydrate containing an aldehyde or ketone functional group having an active α-hydrogen (collectively referred to as a raw material) for forming an oxyhydrocarbon product, where the cathode includes a conductive support substrate, a cocatalyst other than nickel phosphide, and an electrocatalytic coating, and the electrocatalytic coating includes Ni x P y (also referred to herein as "Ni-P") nanoparticles, and x and y represent integers such that the compound is selected from the group consisting of Ni3P, Ni5P2, Ni 12 P5, Ni2P, Ni5P4, NiP2, and NiP3, or an electrocatalytic coating containing Ni x P y nanoparticles is selected from the group consisting of Ni3P, Ni5P2, Ni 12 P5, Ni2P, Ni5P4, NiP2, and NiP3, is further alloyed with Fe2P, and the alloy has a Ni-P:Fe2P ratio of about 99:1 to 1:99 by weight. The conductive support substrate includes a hydrophobic region and a hydrophilic region for assisting the adsorption of feedstock from a gas or aqueous phase and achieving separation from water molecules. At least a portion of the electrocatalytic nanoparticles is located in the hydrophobic region of the conductive support substrate and catalytically interacts with the feedstock by electroreduction to produce an oxyhydrocarbon product; 2) the cocatalyst is arranged to act together with the electrocatalyst by incorporation into a hydrophilic or hydrophobic region, or by dissolution in an electrolyte, or by direct immobilization / incorporation onto the catalyst surface.

[0013] The cocatalyst can include any acid, and the acid can be selected from a Lewis acid or a Bronsted-Lowry acid. For example, the acid can be Zn +2 , Fe +2 , Fe 3+ , Ca 2+ , Mg 2+ , Al +3 AlO + Si 4+ SiO 2+ H3BO3, H x BO y Rz (wherein x, y, and z are each independently integers selected from 0 or 1 to 3, -(x + (-2y) + (z·n)) = -5 or -1 or 0 or 1 or 2 or 3, and n is -1, -2 or -3 for various substitutions for R, and as a result borate esters may be selected from d-block or p-block ions such as B(OH)2(OR) and B(OH)(OR)2, where R = alkyl, aryl, arylalkyl, heteroaryl, heteroarylalkyl, and the heteroatoms of heteroaryl and heteroarylalkyl are selected from nitrogen, oxygen, and sulfur.) and mixtures of two or more thereof.

[0014] The co-catalyst may contain any base, which can be selected from Lewis bases or Bronstead-Lowry bases. The base can be selected from the group consisting of conjugate bases of each of the Lewis acids or Bronstead-Lowry acids mentioned above. Examples include borates, carboxylates, NH3, carbamides, urea, hydrazines, primary amines, secondary amines, tertiary amines, pyridines, and mixtures of two or more of these.

[0015] The cathode can be in contact with an electrolyte solution containing a co-catalyst, or the co-catalyst is HCO3 - or CO3 2- or H + It may be an ionic liquid electrolyte that has a transport function and is in contact with the cathode. Alternatively, the co-catalyst may include an ionomer or a conductive polymer, or modification or doping of the electrode support.

[0016] Furthermore, the co-catalyst may include salts of Cu, Ag, Au, Zn, mixtures of two or more of them, or salts or oxides thereof. The salts or oxides may also be soluble at a suitable pH. Alternatively, the co-catalyst may include simple metals or alloys selected from the group consisting of Cu, Ag, Au, Zn, and their intermetallic compounds. The co-catalyst metal or intermetallic compound may be in the form of molecular ions, nanoparticles, or larger particles.

[0017] While we do not wish to be bound by any particular theory, the above combination of co-catalysts is thought to bind to reaction intermediates, such as but not limited to formate, formyl / formaldehyde, glycoaldehyde, methylglyoxal, or furan derivatives, on the electrocatalyst surface, thereby 1) influencing the binding orientation of the intermediate, and / or 2) activating the intermediate for subsequent reactions with surface-bonded hydrides or other CO2 / CO reaction intermediates, and / or 3) influencing the binding strength of the intermediate, making it stronger or weaker, and / or 4) promoting the formation of new reaction intermediates on the surface. Through these actions, the co-catalyst enhances the carbon product selectivity for specific hydrocarbon or oxyhydrocarbon products.

[0018] The cathode can be in contact with an electrolyte solution containing a co-catalyst having a conductive support further containing the same co-catalyst. The conductive support substrate can further incorporate a material to be reduced, thereby the electrocatalytic coating catalytically interacts with the material to be reduced incorporated into the conductive support substrate. Preferably, the material to be reduced includes carbon dioxide, carbon monoxide, a mixture thereof, or any other oxyhydrocarbon molecule containing either an aldehyde or ketone functional group and a reactive alpha-hydrogen. Alternatively, the conductive support substrate may be an ionomer or a conductive polymer.

[0019] Another aspect of the present invention relates to a method for producing oxyhydrocarbon products from water, carbon dioxide and / or carbon monoxide via an electrolytic reaction, comprising the steps of (a) placing the cathode of the above combination together with the anode in an electrolyte, (b) making the anode and cathode conductive contact with an external current source, (c) providing a carbon source of carbon dioxide and / or carbon monoxide to the cathode, and (d) applying an electric current to drive the electrolytic reaction at the cathode, thereby selectively producing oxyhydrocarbon products from carbon dioxide and / or carbon monoxide. In the method, the electrocatalyst and co-catalyst are selected to produce products selected from 2,3-franzioll, 2-formylfuran-3-ol, ethylene glycol, 1,3-propanediol, 1,2-propanediol, their stereoisomers, and combinations thereof.

[0020] Preferably, the source of carbon dioxide, carbon monoxide, or any other oxyhydrocarbon molecule containing either an aldehyde or ketone functional group and a reactive alpha-hydrogen is a flow source. The flow source may be a flow-through reactor.

[0021] A further aspect of the present invention is a method for reducing carbon dioxide to an oxyhydrocarbon product, comprising the steps of (a) placing a cathode together with an anode and a co-catalyst (as described above) in an aqueous electrolyte, wherein the cathode comprises a conductive support substrate, a co-catalyst (as described above), and Ni x P y The electrocatalytic coating includes nanoparticles of which x and y are compounds of Ni3P, Ni5P2, and Ni 12The present invention relates to a method comprising the steps of: (b) bringing the anode and cathode into conductive contact with an external current source; (c) providing a flow source of carbon dioxide to the cathode; and (d) applying an electric current to drive an electrolytic reaction that generates electrons at the anode that are delivered to the cathode, thereby producing an oxyhydrocarbon product from carbon dioxide, electrons and water, wherein the electrocatalyst and co-catalyst are selected such that the oxyhydrocarbon product produced is selected from carbohydrates, carboxylic acids, aldehydes, ketones and mixtures of two or more thereof.

[0022] Another aspect of the present invention is a method for reducing carbon dioxide to oxyhydrocarbon products, comprising the steps of (a) placing a cathode together with an anode and a co-catalyst in an electrolyte, wherein the cathode comprises a conductive support substrate and an electrocatalytic coating, and the electrocatalytic coating is Ni x P y The compound contains nanoparticles, where x and y are Ni3P, Ni5P2, and Ni 12 The present invention relates to a method comprising the steps of (b) bringing the anode and cathode into conductive contact with an external current source, (c) providing a flow source of carbon dioxide to the cathode, and (d) applying an electric current to drive an electrolytic reaction to produce an oxyhydrocarbon product from carbon dioxide, wherein the electrocatalyst and co-catalyst are selected such that the oxyhydrocarbon product produced is selected from carbohydrates, carboxylic acids, aldehydes, ketones and mixtures thereof. The co-catalyst may be present on a conductive support, in an electrolyte, or both, and the co-catalyst may bond to an aldehyde, ketone, carboxylic acid, diol or alcoholic functional group of a reaction intermediate, thereby activating it for further reaction with an electrocatalyst; (b) bringing the anode and cathode into conductive contact with an external current source; (c) providing a flow source of carbon dioxide to the cathode; and (d) applying an electric current to drive an electrolytic reaction to generate electrons at the anode that are delivered to the cathode. The electrocatalyst and co-catalyst are selected such that the oxyhydrocarbon product produced is selected from carbohydrates, carboxylic acids, aldehydes, ketones and mixtures of two or more thereof. The co-catalyst may include a metal selected from Cu, Ag, Au, Zn and their intermetallic compounds. The co-catalyst metal or intermetallic compound may be nanoparticles. [Brief explanation of the drawing]

[0023] [Figure 1] This figure shows the Faraday efficiencies (electron efficiencies) of Ni3P, Ni12P5, Ni2P, Ni5P4, and NiP2 electrocatalysts in CO2-purged potassium bicarbonate (electrolyte) in the absence of co-catalysts. The potential has been corrected for the pH dependence of the standard H2 electrode (i.e., reversible H2 electrode, RHE). [Figure 2] This figure shows the Faraday efficiency (electron efficiency) of Ni2P electrocatalysts with two different co-catalysts in CO2-purged potassium bicarbonate (electrolyte). The current difference between the two catalyst systems and the electrocatalyst without co-catalysts indicates the effect of the combined catalyst system. The potential was corrected for the pH dependence of the standard H2 electrode (i.e., reversible H2 electrode, RHE). [Figure 3] Figure 3A shows the proposed changes in the mechanism caused by the addition of the various co-catalysts described above. Figure 3B shows the proposed changes in the mechanism caused by the addition of the various co-catalysts described above. Figure 3C shows the proposed changes in the mechanism caused by the addition of the various co-catalysts described above. Figure 3D shows the proposed changes in the mechanism caused by the addition of the various co-catalysts described above. [Figure 4] Figure 4A shows the 1H NMR of the product showing the change in selectivity upon addition of 25 mM boric acid. The electrocatalyst is a solid pellet of Ni2P at 0 V versus RHE at pH 7.5. Figure 4B shows the corresponding HPLC (refractive index detector trace) showing the change in selectivity upon addition of 25 mM boric acid. The electrocatalyst is a solid pellet of Ni2P at 0 V versus RHE at pH 7.5. Comparison with the electrolyte blank and pure ethylene glycol standard is shown. [Figure 5] This figure shows the 1H NMR spectrum illustrating the change in product selectivity when Cu metal is deposited on an electrocatalyst (solid pellet of Ni2P at 0V versus RHE at pH 1). [Modes for carrying out the invention]

[0024] The technology of this disclosure relates to the preparation of oxyhydrocarbons, which are common chemical feedstocks that can be easily handled by existing transport and export facilities.

[0025] CO2 reduction can be carried out by direct electrolysis at room temperature, but at least four electrons (e) are needed to form a valuable fuel (eqs.3-7). - ) is necessary. From the listed potentials, CO2 reduction is simpler 2e - It becomes clear that this occurs in the thermodynamic competition between the hydrogen evolution reaction (HER) (RHE in H2 at U=0V vs. 1atm) and most oxyhydrocarbon products (all formed at approximately the same potential).

[0026] [ka]

[0027] Therefore, the challenge is to produce an electrocatalyst that preferentially provides hydrogen equivalents (H* or hydrides) to reduce CO2 to specific carbon products, rather than forming a mixture of products or H2. Conventional CO2 reduction electrocatalysts based on Cu electrodes form a mixture of products, and optimized results show a selectivity for hydrocarbons of 72.3% achieved at -1.04V against a reversible hydrogen electrode ("RHE") (CH4 was the main product), which is about 1.2V negative than the thermodynamic limit of +0.16V against RHE. However, such a large overpotential significantly reduces energy efficiency and eliminates the applicability of this method to the production of synthetic fuels. Nevertheless, copper remains the best-performing single-component transition metal DCRR electrocatalyst to date.

[0028] Feasible technologies for producing fuel from CO2 must be quantitatively compared with industrial procedures. Currently, industrial methanol production from CO is estimated to have an energy efficiency of 51%. The theoretical maximum energy efficiency of DCRR is 73%, assuming an overpotential of 0V and complete recovery of the product, indicating that DCRR is a technology that can theoretically significantly exceed current industrial standards. Assuming oxygen evolution is an anode reaction, the efficiency of the electrochemical reduction of CO2 to CH4 (also referred to herein as "electro-reduction") is currently 13% on a Cu surface.

[0029] Replacing electrocatalysts (electrodes) represents an expensive downtime investment for any commercial process; therefore, maintaining a long lifespan of superior electrocatalytic performance is crucial. Currently, there are very few examples of testing exceeding 2 hours of DCRR on transition metal electrodes. The electrocatalyst of this invention aims for at least 16 hours of continuous activity. Industrial applications require stability significantly longer than a few hours. For example, industrial anodes (RuO2) for chlor-alkali processes. x and IrO x (Based on) has a lifespan of approximately 7 years.

[0030] Ni3P, Ni 12 P5, Ni2P, Ni5P4, and NiP2 are currently synthesized as highly compressed powders that form a nearly flat surface for direct CO2 reduction electrocatalysts of the type of the present invention. This allows for direct observation of catalytic activity at the most stable crystalline phase termination and is directly comparable to the optimized Cu foil of the prior art. Their activity as DCRR electrocatalysts in the absence of co-catalysts is shown in the following data (Figure 1). The selectivity of these electrocatalysts for DCRR has been found to be tunable based on composition and structure. The high natural abundance of both Ni and P elements ensures the scalable production of these electrocatalysts for industrial applications.

[0031] Furthermore, it was discovered that the nickel phosphide electrocatalyst described above, together with the co-catalyst, alters the carbon product selectivity by interacting with the selected reaction intermediate. These co-catalysts are all Lewis acids or Brønsted-Lawry acid Al. +3 AlO + Si 4+ SiO 2+ , H3BO3, H x BO y R z (In the formula, x, y, and z are integers independently selected from 0 or 1 to 3, and -(x+(-2y)+(z·n))=-5 or -1 or 0 or 1 or 2 or 3, and n is -1, -2 or -3 for various substitutions for R, and as a result, borate esters include, for example, B(OH)2(OR) and B(OH)(OR) )2 The boronic acid esters include, for example, RB(OH)2 and RB(OR')2, where R and R' = alkyl, aryl, arylalkyl, heteroaryl, heteroarylalkyl, and the heteroatoms of heteroaryl and heteroarylalkyl are selected from nitrogen, oxygen, and sulfur, as well as mixtures of two or more thereof, or oligomers / polymer chains.

[0032] Furthermore, the anion exchange membrane is CO3 2- This allows for the transport of neutral CO2 (aqueous solution) and H2O to the electrocatalyst surface, while also enabling the transport of H2O due to charge repulsion. + This restricts accessibility. DCRR activity is known to be pH-sensitive, in that higher pH improves selectivity but limits CO2 availability. Therefore, locally controlling proton availability by using anion exchange membranes rather than increasing the pH of the bulk solution strongly supports DCRR over HER. Accordingly, one aspect of the present invention relates to a composite electrode of the binary electrocatalyst and co-catalyst of the present invention with various polymers having anionic conductive properties near the electrocatalyst surface.

[0033] Furthermore, the hydrophobic polymer material incorporated into the electrode substrate enables the transport of neutral CO2(g) to the electrocatalyst and co-catalyst. DCRR critically relies on high-volume transport when manufacturing liquid products or operating in liquid electrolytes. Therefore, locally reducing the transport resistance to gas molecules by the exclusion of water caused by hydrophobic domains strongly supports high DCRR reaction rates. Accordingly, one aspect of the present invention relates to a composite electrode of the above electrocatalyst and co-catalyst in various polymers having various hydrophobic properties or various compositions in order to adjust the hydrophobicity of the electrode ensemble.

[0034] In another embodiment, the use of anionic ionomers is HCO3 - or CO3 2- or H + It may be replaced with an ionic liquid having a transport functional group. In other embodiments of the present invention, a bicarbonate, a carbonate, or H + The functional group is bonded to either the polymer or a soluble molecule, and the soluble molecule may be of variable size: small, medium, or large.

[0035] Results using only an electrocatalyst Nickel phosphide (Ni3P, Ni) has a different structure. 12 Figure 1 shows some data for P5, Ni2P, Ni5P4, and NiP2. Figure 1 also shows how the transition from Ni3P (high nickel content) to NiP2 (high phosphorus content) and the increase in DCRR selectivity at low applied voltages can be observed. At higher applied voltages, H2 generation is more favorable than DCRR. Ni2P and NiP2 show the highest selectivity for DCRR, but the former prefers the C4 product and the latter prefers the C3 product. This indicates that for binary compounds (same binary elements) in this family where only the crystalline phase changes, there are clear differences in how the surface binds to CO2, and therefore to the carbon product.

[0036] Electrocatalyst Ni3P, Ni 12None of P5, Ni2P, Ni5P4, or NiP2 exhibit the formation or release of CO as a gaseous product, presumably because no irreversible bonds are formed on their surfaces.

[0037] Achieving highly selective control of CO2 electrolysis using a co-catalyst. As defined herein, a co-catalyst encompasses all possible additives to the nickel-phosphorus binary compound that modify the performance of the catalytic process without being consumed by themselves. The additives include any element or compound that is not a nickel-phosphorus binary compound, in an amount of less than 50% by weight of the composition.

[0038] This co-catalyst binds to the reaction intermediate on the surface or in solution, and 1) affects the bond orientation of the intermediate, and / or 2) activates the intermediate for subsequent reactions with surface-bonded hydrides or other CO2 / CO reaction intermediates, and / or 3) affects the bond strength of the intermediate, making it stronger or weaker, and / or 4) promotes the formation of new reaction intermediates on the surface.

[0039] Therefore, the ionic co-catalysts of the present invention are conjugate acid / base pairs and charged ions, which are used with transition metal phosphide electrocatalysts as dopants, either incorporated into the electrocatalyst synthesis, co-deposited on transition metal phosphide electrocatalysts, or added to the electrolyte in which the electrodes are bathed. Other chemical terms used to describe these co-catalysts are Lewis acid / base pairs, Brønsted-Lowry acid / base pairs (also known as Brønsted acid / base), and cation / anion, respectively. In particular, for co-catalysts in electrolyte solutions, pH adjustment can provide a mixture of acidic and conjugate base species. Thus, boric acid can be added to an electrolyte solution, and a mixture of boric acid and borate species can be obtained by adjusting the pH. Similarly, sodium borate can be added to an electrolyte solution, and a mixture of boric acid and borate can be obtained by adjusting the pH. In another embodiment, the co-catalyst is nonionic and influences the reaction of the transition metal phosphide electrocatalyst as a surface deposit (or catalyst surface dopant) bonding reaction intermediate, so as to be able to react with a DCRR intermediate bonded to the transition metal phosphide surface or the transition metal phosphide electrocatalyst surface.

[0040] Here, it is shown that the product selectivity of CO2 reduction on nickel phosphide can be greatly altered by the addition of co-catalysts (i.e., species or materials that are not consumed and can exist as soluble molecules in the electrolyte, molecules adsorbed on the electrocatalyst surface, incorporated into the electrocatalyst support or ionomer or conductive polymer, or as dopant ions in the entire electrocatalyst bulk). These two classes of co-catalysts are shown in Figure 2 and its associated Table 1, showing the range of products and their yields independently formed on Ni2P using three different soluble co-catalysts at a fixed pH (7.5) in the electrolyte solution. Lewis acid-base pairing: borate / borate (H3BO3 / B(OH)4 - ) or cationic Brønsted acid / base pair hexamethylenetetramine (C6H 12 N4H + / C6H 12When N4) is added to the C2 product ethylene glycol (93% and 72%, respectively), a large shift in product selectivity occurs compared to the baseline product (mainly C3+C4). The change in carbon selectivity relative to the benchmark Ni2P electrocatalyst is maintained across the applied potential range, as shown in Figure 2. In contrast, Mg 2+ The co-catalyst (classified as a cation or Lewis acid) forms a minimal increase in C2 product and formic acid levels compared to electrocatalyst alone, although this is still less than 15% at most, likely due to the solubility limit of the MgCO3 co-catalyst. Methods of improvement may include the use of other co-catalysts with higher solubility, or the incorporation of the co-catalyst into a conductive catalyst support primarily located in hydrophilic regions. As the applied negative bias increases, the yield of oxyhydrocarbon products decreases, competing with the increase in H2 yield in all electrocatalysts, with or without the co-catalyst. This provides direct insight into the mechanism (see Figures 3A–3D).

[0041] [Table 1]

[0042] Reaction mechanism (Figures 3A-3D) While we do not wish to be bound by any particular theory, the inventors of this invention have found that surface-bonded *C2 intermediates and initial H * We believe that competition with the regeneration of the coating surface indicates that the reaction forming the C2 precursor into the final MEG product can be dissociated from the electrocatalyst. This information will guide us on what type of co-catalyst is needed to enhance certain oxy hydrocarbons more than other DCRR products.

[0043] Figures 3A and 3B. Glycoaldehyde reduction: Lewis (or Brønsted) acid activation of the aldehyde group of surface-bound glycoaldehydes*. This activates the aldehyde for reduction to the corresponding alcohol. This mechanism is supported by activation at low pH.

[0044] Figure 3C. Glycoaldehyde-formaldehyde disproportionation reaction: Lewis base or Brønsted base-catalyzed hydrolysis of formaldehyde* bound to the surface sets up its disproportionation reaction with glycoaldehyde* bound to the surface (by intermolecular hydride transfer) to form formic acid and ethylene glycol, respectively. The base-catalyzed disproportionation reaction of two carbonyls that produce a carboxylic acid and an alcohol is an example of a type of reaction called the Cannizzaro reaction. The formic acid* product is further electrolytically reduced to formaldehyde* at the electrode surface, and finally consumes all CO2 to produce ethylene glycol.

[0045] Figure 3D. Oxalic acid pathway: A third possible pathway that fits the available data is CO2 insertion into the CH bond of formic acid* bonded to the surface. This step forms an oxalate that can further react with the surface hydride to produce ethylene glycol and water.

[0046] Boric acid or boronic acid or its corresponding ester is known to reversibly bond to diols such as ethylene glycol. However, the present invention incorporates the discovery that by bonding an intermediate, the co-catalyst reduces the desorption energy of the intermediate from the surface, thereby causing it to become a primary product.

[0047] Ni2P was prepared by solid-phase synthesis and pressed into pellets. The test involved a CO2 saturated electrolyte (0.5M KHCO3, 25mM hexamethylenetetraamine, 25mM boric acid, or 1.5mM Mg). 2+ The experiment was conducted under a specific applied potential in a solution containing one of three co-catalysts selected from the following. The test was performed for 16 hours per experiment at ambient pressure and temperature, pH 7.5. The ambient temperature was typically 70°F to 80°F. The headspace composition was monitored by gas chromatography, and the liquid product was analyzed by HPLC and NMR.

[0048] Figure 4A shows the electrolytes 1The 1H NMR spectrum is shown, with the main peak being ethylene glycol (as confirmed by HPLC trace figure 4B), confirming the selectivity shift caused by the addition of the co-catalyst.

[0049] The co-catalysts are Ni3P, Ni5P2, and Ni 12 P5, Ni2P, Ni5P4, NiP2, and NiP3, and the above Ni x P y This is effective when applied to all members of the nickel phosphide family electrocatalysts disclosed above, including electrocatalytic nanoparticles of an alloy of one or more compounds with Fe2P, wherein the alloy has a Ni-P:Fe2P ratio of 100:0 to 0:100 wt%, preferably about 99:1 to 1:99 wt%. Particularly preferred nickel phosphides for co-catalysis are Ni3P, Ni 12 Examples include P5, Ni2P, Ni5P4, and NiP2.

[0050] The co-catalyst concentration in the electrolyte can range from very low concentrations to its solubility limit, typically from about 0.1 mM to about 10 M. Preferably, the co-catalyst concentration range is about 0.5 mM to about 5 M. Alternatively, the co-catalyst concentration range may be about 1 mM to about 1 M, or about 1 mM to about 100 mM, or about 1.5 mM to about 50 mM, or about 1.5 mM to about 25 mM. The concentration of the soluble co-catalyst may range from about 0.1 mM to about 100 mM. The co-catalyst can be present in the electrolyte at about 1.5 mM or about 25 mM.

[0051] Numerous ranges of values ​​are provided as disclosed herein. Unless otherwise explicitly indicated in the context, each intervening value up to one-tenth of the lower limit between the upper and lower limits of a range is also specifically disclosed. Each smaller range between any stated or intervening value within a stated range and any other stated or intervening value within that stated range is included in the present invention. The upper and lower limits of these smaller ranges may be independently included in or excluded from the range, and each range in which either limit is included in a smaller range, neither limit is included in a smaller range, or both limits are included in a smaller range is also included in the present invention, subject to any specifically excluded limits within the stated range. If a stated range includes one or both limits, the range excluding one or both of the limits that they include is also included in the present invention. The term “about” generally includes up to ±10% of the indicated number. For example, “about 10%” could mean a range of 9% to 11%, and “about 20” could mean 18 to 22. Preferably, "approximately" includes up to ±6% of the indicated value. Alternatively, "approximately" includes up to ±5% of the indicated value. Other meanings of "approximately" may be apparent from contexts such as rounding, so for example, "approximately 1" could also mean between 0.5 and 1.4.

[0052] Alternatively, a co-catalyst in the form of a second catalytic metal on the surface may be added, or doping with another metal (or metal ion) in or on the surface, or within the bulk of the electrocatalyst is possible. The co-catalysts of the present invention encompass all possible additives to the nickel-phosphorus binary compound that modify the performance of the catalytic process without being consumed by themselves.

[0053] This second co-catalyst metal or metal ion must be selected from the group known to promote the reduction of CO2 or CO or other reaction intermediates from DCRR. This includes, but is not limited to, metals such as Cu, Ag, Au, Zn, and their intermetallic compounds or oxide compounds. The co-catalyst metal, intermetallic compound, or oxide is preferably a nanoparticle with a size in the range of about 0.1 to about 1000 nm. The co-catalyst particle size may be about 0.5 nm to about 1000 nm, or about 0.5 nm to about 500 nm, or about 0.5 nm to about 50 nm, or about 0.5 nm to about 20 nm. The co-catalyst particle size may be about 0.1 nm to about 500 nm, or about 0.1 nm to about 50 nm, or about 0.1 nm to about 5 nm, or about 0.1 nm to about 2 nm.

[0054] The deposition of such co-catalysts on nickel phosphide alters the selectivity of the reaction by changing the aggregation and binding affinity of reaction intermediates on the surface. (Figure 5) 1 The 1H NMR spectrum shows the CO2 reduction products formed when copper metal or soluble Cu salt on Ni2P nanoparticles is electrodeposited at 0V vs. RHE and acidic pH. The data demonstrate the formation of two C5 compounds (3-hydroxy-2-francarboxaldehyde and 2-hydroxy-3-francarboxaldehyde).

[0055] Flow System In this specification, binary transition metal phosphide electrocatalyst compounds, combined with co-catalysts, have been demonstrated to exhibit remarkable DCRR carbon product selectivity for hydrocarbons or oxyhydrocarbons. When switched to a flow-through reactor in which CO2 continuously passes over the working electrode, carbon-containing products are formed at higher rates and concentrations. This constitutes another aspect of the present invention.

[0056] One aspect of the present invention is a cathode for the direct electrochemical reduction of carbon dioxide and / or carbon monoxide to an oxybicarbonate product together with any other additive hydrocarbon molecule containing either an aldehyde or ketone functional group and a reactive alpha-hydrogen, wherein the cathode comprises a conductive support substrate and an electrocatalytic coating, the electrocatalytic coating being Ni x P y The compound contains nanoparticles, where x and y are Ni3P, Ni5P2, and Ni 12 Represents an integer selected from P5, Ni2P, Ni5P4, NiP2, and NiP3, or Ni x P y The electrocatalytic coating containing nanoparticles of Ni3P, Ni5P2, and Ni 12 The invention relates to a combination of a cathode, selected from P5, Ni2P, Ni5P4, NiP2, and NiP3, further alloyed with Fe2P, the alloy having a Ni-P:Fe2P ratio of about 99:1 to 1:99 wt%, the conductive support substrate comprising hydrophobic and hydrophilic regions to assist in the adsorption of carbon dioxide and / or carbon monoxide from the gas or aqueous phase to achieve separation from water molecules, at least a portion of the electrocatalytic nanoparticles located in the hydrophobic region of the conductive support substrate, catalytically interacting with carbon dioxide and / or carbon monoxide by electroreduction to produce oxyhydrocarbon products, and 2) a co-catalyst other than nickel phosphide arranged to work together with the electrocatalyst for the reduction of carbon dioxide and / or carbon monoxide. The Ni-P:Fe2P ratio can be about 99:1 to about 1:99 wt%, the Ni-P:Fe2P ratio can be about 95:5 to about 5:95 wt%, or the Ni-P:Fe2P ratio can be about 90:10 to about 10:90 wt%. The Ni-P:Fe2P ratio can be approximately 25:75 to 75:25 by weight%.

[0057] The co-catalyst may contain an acid, which can be selected from Lewis acids or Bronsted-Lowry acids. The acid is Zn +2 Fe +2 Fe 3+ Ca 2+ Mg 2+ , Al +3 AlO +Si 4+ SiO 2+ , H3BO3, H x BO y R z (wherein x, y, and z are each independently integers selected from 0 or 1 to 3, and -(x + (-2y) + (z·n)) = -5 or -1 or 0 or 1 or 2 or 3, and n is -1, -2 or -3 for various substitutions for R, so that borate esters include, for example, B(OH)2(OR) and B(OH)(OR)2, and R = alkyl, aryl, arylalkyl, heteroaryl, heteroarylalkyl, and the heteroatoms of heteroaryl and heteroarylalkyl are selected from nitrogen, oxygen and sulfur), and can be selected from the group consisting of two or more mixtures thereof. Suitable R=alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, iso-butyl, tert-butyl, n-pentyl, iso-pentyl, sec-pentyl, tert-pentyl, and neopentyl. Suitable R=aryl groups include, but are not limited to, phenyl, biphenyl, and naphthyl groups, which may be optionally substituted with one or more halogens, alkoxys, alkylthios, alkyls, cyanos, nitros, alkylsulfoxides, alkylsulfones, and arylsulfones.

[0058] The co-catalyst is a compound of formula H having an oxidation state of -5, -1, 0, +1, +2, or +3. x BO y R z It can contain boron compounds, and as a result integers x, y, and z are defined by the formula -(x + (-2y) + (z·n)) = -5 or -1 or 0 or 1 or 2 or 3, where n is -1, -2 or -3 for various substitutions on R, and R is defined as above. In addition to borate esters B(OH)2(OR) and B(OH)(OR)2 where R = CH3, alkyl, C6H5, aryl, etc., it also includes (C6H5)3B(triphenylborane) and H3NBH3 when x or y is 0, and H3BO3(boric acid) and BH3 when z is 0.

[0059] The co-catalyst may contain a base, which can be selected from Lewis bases or Bronsted-Lowry bases. The base can be selected from NH3, carbamides, urea, hydrazine, primary amines, secondary amines, tertiary amines, pyridine, and mixtures of two or more of these.

[0060] The cathode can be in contact with an electrolyte solution containing a co-catalyst, or the co-catalyst is HCO3 - or CO3 2- or H + It may be an ionic liquid electrolyte that has a transport function and is in contact with the cathode. Alternatively, the co-catalyst may be an ionomer or a conductive polymer.

[0061] Furthermore, the co-catalyst may include soluble salts of Cu, Ag, Au, Zn, mixtures of two or more of them, or salts or oxides thereof. The salts or oxides become soluble at the appropriate pH. Alternatively, the co-catalyst may include simple metals or alloys selected from Cu, Ag, Au, Zn, and their intermetallic compounds. The co-catalyst metal or intermetallic compound may be in the form of nanoparticles. The co-catalyst metal, intermetallic, or oxide nanoparticles have a size in the range of about 0.1 to about 1000 nm. The co-catalyst particle size may be about 0.5 nm to about 1000 nm, or about 0.5 nm to about 500 nm, or about 0.5 nm to about 50 nm, or about 0.5 nm to about 20 nm. The co-catalyst particle size may be about 0.1 nm to about 500 nm, or about 0.1 nm to about 50 nm, or about 0.1 nm to about 5 nm, or about 0.1 nm to about 2 nm.

[0062] While we do not wish to be bound by any particular theory, it is thought that the above combination of co-catalysts, on the electrocatalyst surface or in solution, bind to the reaction intermediate, 1) influencing the bond orientation of the intermediate, and / or 2) activating the intermediate for subsequent reactions with surface-bonded hydrides or other CO2 / CO reaction intermediates, and / or 3) influencing the bond strength of the intermediate to make it stronger or weaker, and / or 4) promoting the formation of new reaction intermediates on the surface.

[0063] The cathode can be in contact with an electrolyte solution containing a catalyst that has a conductive support further containing the same cocatalyst. The conductive support substrate can further incorporate a material to be reduced, whereby the electrocatalytic coating catalytically interacts with the material to be reduced incorporated in the conductive support substrate. Preferably, the material to be reduced contains carbon dioxide, carbon monoxide, or a mixture thereof. Alternatively, the conductive support substrate can be an ionomer or a conductive polymer.

[0064] Another aspect of the present invention is a method for producing oxyhydrocarbon products from water, carbon dioxide, and / or carbon monoxide via an electrolysis reaction, comprising: (a) disposing a combination of an electrocatalytically coated cathode and a cocatalyst together with an anode in an electrolyte; (b) making electrical conductive contact between the anode and the cathode with an external current source; (c) providing a carbon source of carbon dioxide and / or carbon monoxide to the cathode; and (d) applying a current to drive an electrolysis reaction at the cathode, thereby selectively producing an oxyhydrocarbon product from carbon dioxide and / or carbon monoxide. In the method, the electrocatalyst and the cocatalyst are selected to produce products selected from 2,3-furanediol, 2-formylfuran-3-ol, ethylene glycol, 1,3-propanediol, 1,2-propanediol, their stereoisomers, and combinations thereof.

[0065] Preferably, the source of carbon dioxide and / or carbon monoxide is a flow source. The flow source can be a flow-through reactor.

[0066] A further aspect of the present invention is a method for the reduction of carbon dioxide to an oxyhydrocarbon product, comprising: (a) disposing a cathode together with an anode and a cocatalyst of an acid or a base or a charged ionic species in an aqueous electrolyte, wherein the cathode comprises a conductive support substrate, a cocatalyst comprising an acid or a base or a charged ionic species, and Ni x P yThe electrocatalytic coating of nanoparticles is included, where x and y are compounds of Ni3P, Ni5P2, and Ni 12 The present invention relates to a method comprising the steps of: (b) bringing the anode and cathode into conductive contact with an external current source; (c) providing a flow source of carbon dioxide to the cathode; and (d) applying an electric current to drive an electrolytic reaction in which electrons delivered to the cathode are generated at the anode, thereby producing an oxyhydrocarbon product from carbon dioxide, electrons, and water, wherein the electrocatalyst and co-catalyst are selected such that the oxyhydrocarbon product produced is selected from carbohydrates, carboxylic acids, aldehydes, ketones, and mixtures of two or more thereof.

[0067] Further aspects of the present invention are methods for reducing carbon dioxide to oxyhydrocarbon products, comprising the steps of (a) placing a cathode together with an anode and a co-catalyst in an electrolyte, wherein the cathode comprises a conductive support substrate and an electrocatalytic coating, and the electrocatalytic coating is Ni x P y The compound contains nanoparticles, where x and y are Ni3P, Ni5P2, and Ni 12The present invention relates to a method comprising the steps of (b) bringing the anode and cathode into conductive contact with an external current source, (c) providing a flow source of carbon dioxide to the cathode, and (d) applying an electric current to drive an electrolytic reaction in which electrons delivered to the cathode are generated at the anode, thereby producing an oxyhydrocarbon product from carbon dioxide, wherein the electric catalyst and co-catalyst are selected such that the oxyhydrocarbon product produced is selected from carbohydrates, carboxylic acids, aldehydes, ketones, and mixtures of two or more thereof. The co-catalyst may be a metal selected from Cu, Ag, Au, Zn, and their intermetallic compounds. The co-catalyst metal or intermetallic compound may be nanoparticles.

[0068] The electrocatalysts of the following examples were synthesized, their atomic structures were determined by physical characterization methods, and their HER activity was tested by electrochemical and gas chromatography. The electrocatalysts of the present invention can be supported on a titanium film electrode, for example, by pressing them into pellets, bonding them to a titanium film electrode via silver paint, and encapsulating them in a non-conductive epoxy. Alternatively, the electrocatalysts can be supported on carbon or ceramic powder.

[0069] The as-synthesized electrocatalysts of this disclosure have particle sizes in the range of about 5 nm to about 5000 nm, preferably about 5 nm to about 1000 nm, more preferably about 5 nm to about 500 nm, and even more preferably about 5 nm to about 20 nm. The particle size may be in the range of about 10 to about 4000 nm, or about 25 to about 3000 nm, or about 50 to about 2500 nm. The particle diameter may be at least 100 nm. These particles are part of larger spherical particle aggregates of 0.3 to 1.8 μm. The electrocatalysts have been found to be very durable under electrolytic conditions in both 1 M H2SO4 acid and 1 M NaOH. Evidence is obtained from both electrochemical stability and X-ray fluorescence analysis confirming the atomic composition of the surface, as well as from the physical appearance at the macroscale.

[0070] supporting base material According to another aspect of the present invention, the electrocatalyst comprises a catalytic group and a conductive support substrate supporting a plurality of catalytic groups. The support substrate can incorporate hydrogen cations, and at least some of the catalytic groups supported by the support substrate can catalytically interact with the hydrogen cations incorporated into the support substrate. The support substrate can incorporate water molecules, and at least some of the catalytic groups supported by the support substrate can catalytically interact with the water molecules incorporated into the support substrate. The support substrate can incorporate carbon dioxide, and at least some of the catalytic groups supported by the support substrate can catalytically interact with CO2 molecules incorporated into the support substrate. The support substrate can incorporate a co-catalyst, and at least some of the catalytic groups including the support substrate can catalytically interact with the co-catalysts incorporated into the support substrate.

[0071] The support substrate has multiple porous regions that are microporous, mesoporous, and / or macroporous. The support substrate may be a microporous substrate with an average pore diameter of less than approximately 2 nm. The support substrate may be a mesoporous substrate with an average pore diameter of approximately 2 to approximately 50. The support substrate may be a macroporous substrate with an average particle diameter greater than approximately 50 nm.

[0072] Since the support substrate is conductive to electrons, if a potential difference exists across different points on the support substrate, moving charges within the support substrate are forced to move, generating an electric current between those points. The support substrate can be made conductive by applying a thin layer of the support substrate onto a conductive material. Suitable conductive materials include glassy carbon, carbon nanotubes and nanospheres, titanium foil / wire / mesh / foam / knitted wire mesh, aluminum foil / wire / mesh / foam / knitted wire mesh, fluoride-doped tin oxide (FTO or ((F)SnO2)) coated glass and indium tin oxide (ITO) (or any transparent conductive oxide) coated glass, as well as multilayer structures having a nanostructured semiconductor film coated on a conductive substrate. Other means of making the support substrate conductive are within the scope of the present invention. For example, the support substrate can be in contact with a sensitized semiconductor.

[0073] Preferably, the support substrate has hydrophobic and hydrophilic regions and contributes to the co-catalyst function. With respect to the reduction of water or CO2, although we do not wish to be limited by theory, it is thought that at least a portion of the catalytic groups can be supported in the hydrophobic regions of the support substrate, and once supported, can catalytically interact with water or CO2 molecules in the hydrophilic regions. Effectively, the support substrate is thought to act as an interface between hydrogen cations, water molecules, or CO2 molecules and catalytic groups that are insoluble in aqueous solutions, unlike others.

[0074] Hydrophobic regions may be formed by a hydrophobic polymer backbone, while hydrophilic regions are regions of ionizable functional groups on the polymer backbone that can preferably function as proton-conducting sites. Preferably, the ionizable functional group is a sulfonate group (-SO3H) that loses a proton and forms a negatively charged sulfonate group. Alternatively, the ionizable functional group can preferably form a positively charged functional group that can act as a site for hydroxide or carbonate ion conduction.

[0075] The supporting substrate may be, for example, polysulfone, polysulfonate, and polyphosphonate. The supporting substrate may also include sulfonated fluoropolymers (marketed under the trade name NAFION®). The hydrophobic CF2CF(CF3)O-polymer backbone of NAFION® forms a hydrophobic solid through which aqueous channels, lined with hydrophilic, ionizable sulfonic acid groups, permeate. Investigations of the partial structure of NAFION® coatings on solid surfaces have revealed that the polymer layer contains these hydrophilic channels throughout the hydrophobic region, unlike the rest of the film. These channels enable the diffusion of small molecules such as water.

[0076] Other supporting substrates that may be used include, for example, perfluorinated sulfonic acid polymer cation exchange films such as F-14100, F-930, and F-950, GEFC perfluorinated proton exchange films, polysulfone ionomers, nanostructured films formed by metal oxide nanoparticles appropriately decorated with organic acids including perfluorinated sulfonic acid, and nanostructured films formed by hydrolysis of alkoxysilanes appropriately decorated with organic acids including perfluorinated sulfonic acid.

[0077] Other supporting substrates may include, for example, polyfluorinated alkali exchange membranes (AEMs) that rely on fixed cationic functional groups within the polymer to prevent proton conduction and enable the conduction of mobile anions for conductivity. Examples of commercially available AEMs include TOKUYAMA® AEM. Heterogeneous-homogeneous colloidal systems, two-phase mixtures (stabilized and unstabilized with surfactants), conductive polymers (e.g., poly(3,4-ethylenedioxythiophene) (PEDOT)), surface-modified silica, and titania are also within the scope.

[0078] Other supporting substrates that can be used to contribute to the co-catalyst functional group include borate / boronic acid or amine / ammonium functionalized polymers having an alkyl or aryl or polyfluorinated polymer backbone.

[0079] Other supporting materials that can be used to contribute to the hydrophobic functional domain include alkyl, aryl, or polyfluorinated polymer backbone polymers.

[0080] Any means of contacting the electrocatalyst with water, CO2, or a carbonate mineral is within the scope of the present invention. The electrocatalyst can be immersed in a solution containing water molecules. The solution can be an aqueous solution containing an electrolyte. The aqueous solution may be a solution from which water is preferentially removed (i.e., solid-liquid separation). For example, if the aqueous solution is saline or seawater, the water can be removed and the salt left behind (i.e., desalination). In one example, about 0.5 M of electrolyte is sufficient.

[0081] The following examples are provided to further illustrate the methods and compositions of the present invention. These examples are illustrative and are not intended to limit the scope of the present invention. [Examples]

[0082] [Example 1] Electrode fabrication 1 g of electrocatalyst powder was mixed with 250 μL of 5% NAFION® suspension, which had been pre-neutralized with NaOH. The electrocatalyst powder was continuously mixed with the NAFION® suspension using a mortar and pestle until dry. To ensure complete drying, these were further dried under vacuum for several hours.

[0083] The resulting electrocatalyst / polymer composite was pressed in a 30 mm diameter die under a pressure of 5 to 29 tons. The resulting pellets were attached to a conductive aluminum support using Kapton tape. The geometric surface area was determined by applying a silicone polymer gasket with predetermined openings to the exposed surface.

[0084] [Example 2] Electrochemical measurement All solutions were prepared using MILLIPORE® water. All electrochemical measurements used a three-electrode configuration with NAFION® membranes or anion-exchange membrane separators in the working and counter compartments. Pt or Ir / C electrodes were used as counter electrodes during measurements. A Hg / HgSO4 (Sat'd KCl) reference electrode was used and calibrated against a commercially available saturated calomel electrode (Hack) at open-circuit potential before each measurement. Chronoamperometric data were manually corrected for IR drop by measuring IR drop before and after experiments and manually applying the correct bias.

[0085] The electrolyte was prepared from MILLIPORE® water using high-purity grade reagents. Furthermore, as a further precaution to remove potential metal impurities, the solution was treated with K + -The solution was filtered through a CHELEX® 100 matrix. The electrolyte was stored in a Piranha washing flask until use. Immediately before measurement, the electrolyte was saturated with CO2 (Airgas CD1200) washed to less than 6 ppm of CH4 (the main hydrocarbon impurity) using a Supelco hydrocarbon trap (Sigma).

[0086] Product analysis was performed using an HP5890 Series II GC equipped with a 5A MSieve (Restek) 0.53 mm capillary column, with Ar carrier gas (Supelco hydrocarbons, washed for hydrocarbons and moisture on the moisture trap). Calibration was performed using certified gas mixtures, namely Airgas' 1.04% CH4 / Ar, 1.02% H2 / Ar, and similarly, Airgas' pure C2H4.

[0087] Catalyst production: Solid state synthesis A stoichiometric excess of 1.5 mol% red phosphorus (Alfa-Aesar 99%) and a stoichiometric amount of nickel (Sigma-Aldrich < 150 μm) were thoroughly mixed in a mortar. After washing with Ar, the mixture was transferred to a vacuum-sealed quartz tube by 2-3 backfills. The vacuum-sealed tube was placed in a furnace and raised to 700°C, where it was maintained for 24 hours. The ramp rate was kept moderate to avoid excessive heating during the reaction. The temperature was raised from 80°C to 250°C over 580 minutes with a residence time of 360 minutes, then to 350°C over 300 minutes with a residence time of 200 minutes, then to 450°C over 300 minutes with a residence time of 200 minutes, and finally to 700°C over 350 minutes with a residence time of 24 hours. The sample was then cooled to room temperature under ambient conditions. The sample purity was confirmed by powder X-ray diffraction (PXRD), additional Ni or P was added as needed, the mixture was mixed and sealed as described above, and reheated using an accelerated sequence (580 minutes from 80°C to 750°C with a residence time of 24 hours).

[0088] Nickel phosphide nanoparticles were prepared starting from 20 nm Ni nanoparticles (99.9% USNano Ltd.) lightly mixed with 101.5 mol% red phosphorus in a glove box under argon. The sample was sealed in a vacuum quartz tube and slowly heated to 450°C with a residence time of 48 hours. The gradient was 80°C to 175°C over 580 minutes, followed by a residence time of 360 minutes, an ascent to 250°C over 580 minutes, followed by a residence time of 360 minutes, an ascent to 350°C over 360 minutes, followed by a residence time of 300 minutes, followed by a final ascent to 450°C over 360 minutes, followed by a residence time of 48 hours. The sample was cooled to room temperature under ambient conditions, and the phase purity was confirmed by PXRD. Subsequently, as in the solid-state reaction of 1), additional phosphorus could be added in air. The ramp rate for additional phosphorus addition was 80°C to 450°C over 580 minutes with a residence time of 48 hours. Occasionally, small impurities of Ni(PO3)2 form during exposure to air, so this phase was removed by acid washing in dilute HCl (concentrated HCl to water at a volume ratio of approximately 1:10).

[0089] The crystalline phase was characterized using a Bruker AXS D8 Advance X-ray diffractometer with Cu Kα1 radiation (1.54056 Å), scan times of 1 or 12 hours, and a 2θ range of 15–70° or 10–120°. Samples were analyzed before electrochemical testing by dispersing the powder between two glass microscope slides.

[0090] [Example 3] Synthesis of Ni2P electrocatalyst The electrocatalyst was synthesized using a hydrothermal method. In a typical experiment, 3.685 g of NiCl26H2O (Sigma-Aldrich) and 1.09 g of hexamethylenetetramine (Sigma-Aldrich) were dissolved in 340 ml of Millipore water. The solution was thoroughly mixed with 75 g of red phosphorus (Alfa-Aesar, 98.9%, 325 mesh) by stirring. The mixture was placed in a PTFE-lined autoclave and heated at 180°C for 10 hours. After recovery, the sample was washed with water, 3% hydrochloric acid, water, and acetone, and then dried overnight under vacuum at 30-60°C. The final product was confirmed by PXRD.

[0091] [Example 4] Characterization of Ni2P nanoparticles PXRD analysis was performed using a Bruker AXS D8 Advance with a Cu Kα X-ray tube (1.546 Å), with scan times of 1 hour or 12 hours and a 2θ range of 15–70° or 10–120°. Samples were analyzed by dispersing the powder on a glass microscope slide and planarizing the powder surface using another glass slide before electrochemical testing.

[0092] Catalyst production: Hydrothermal method or solvothermal method The nanoparticles were also successfully prepared by hydrothermal or solvothermal methods, as described in the literature.

[0093] Henkes,A.E.,and Schaak,R.E.(2007).Trioctylphosphine:A general phosphorus source for the low-temperature conversion of metals into metal phosphides.Chemistry of Materials,19(17),4234-4242.doi:10.1021 / cm071021w Laursen,A.B.,Patraju,K.R.,Whitaker,M.J.,Retuerto,M.,Sarkar,T.,Yao,N.,Dismukes,G.C.(2015).Nanocrystalline Ni5P4:a hydrogen evolution electrocatalyst of exceptional efficiency in both alkaline and acidic media.Energy Environ.Sci.,8(3),1027-1034.doi:10.1039 / C4EE02940B Muthuswamy,E.,Savithra,G.H.L.,and Brock,S.L.(2011).Synthetic Levers Enabling Independent Control of Phase,Size,and Morphology in Nickel Phosphide Nanoparticles.ACS Nano,5(3),2402-2411.doi:10.1021 / nn1033357 Prins,R.,and Bussell,M.E.(2012).Metal Phosphides:Preparation,Characterization and Catalytic Reactivity.Catalysis Letters,142(12),1413-1436.doi:10.1007 / s10562-012-0929-7 The electrochemical cell and electrolyte were purged for 20–60 minutes with Grade 4.0 CO2 further purified using a hydrocarbon trap (Supelpure HC), and then current efficiency was measured. The CO2 flow during electrolysis was measured at 5 sccm using a gas mass flow controller. A constant potential was applied for 16–20 hours. A GC autosampler was injected with 500 μL of sample from the effluent gas every 30 minutes. The current efficiency (CE) was then calculated using the following formula.

[0094]

number

[0095] In the formula, n is the number of moles of a given product, F is the Faraday constant, and e is the number of electrons required to produce one molecule of the product (2 for H2, 8 for CH4, and 12 for C2H4).

[0096]

number

[0097] is the gas flow rate (ml / s) divided by the sample volume (0.50 mL), and I is the electric current.

[0098] [Example 8] Gas chromatography An HP5890 series II gas chromatograph, equipped with TCD and FID detectors arranged in series and a 30 m megabore molecular sieve 5A column (Restek), was used to quantify the gaseous product. The GC was calibrated with gas standards, and the number of moles of product in the cell headspace was determined by the ideal gas law.

[0099] [Example 9] Reaction in the presence of a co-catalyst Ni2P was prepared by solid-state synthesis and pressed into pellets as described in Calvinho, K.U.D., Laursen, A.B., Yap, K.M.K., Goetjen, T.A., Hwang, S., Mejia-Sosa, B., Lubarski, A., Teeluck, K.M., Murali, N., Hall, E.S., Garfunkel, E., Greenblatt, M., and Dismukes, G.C. “Selective CO2 Reduction to C3 and C4 Oxyhydrocarbons on Nickel Phosphides at Overpotentials as Low as 10 mV” Energy & Environmental Science, 2018, 11, 2550 - 2559.

[0100] The Ni2P pellets were tested at a constant applied potential in a CO2-saturated electrolyte (a solution containing 0.5 M KHCO3 and a cocatalyst (25 mM hexamethylenetetramine, 25 mM boric acid, or 1.5 mM Mg 2+ )). The tests were carried out at ambient pressure and temperature, pH 7.5, for 16 hours per experiment. The composition of the headspace was monitored by gas chromatography, and the liquid products were analyzed by HPLC and NMR according to the method described in Calvinho et al, Energy & Environmental Science, 2018, 11, 2550 - 2559. Figure 4A shows the NMR of the electrolyte whose main peak is ethylene glycol, confirming the selectivity shift caused by the addition of the cocatalyst. This result is supported by HPLC using a refractive index detector showing boric acid and ethylene glycol as the main peaks (Figure 4B).

[0101] The deposition of metal or metal cation cocatalysts onto nickel phosphide also changes the selectivity of the reaction by changing the ensemble and binding affinity of the reaction intermediates on the surface. Figure 5 1The ¹H NMR spectra show the CO2 reduction products formed when soluble Cu salts were electrodeposited onto copper metal or Ni2P nanoparticles at 0V vs. RHE and acidic pH. The data demonstrate the formation of two C5 compounds (3-hydroxy-2-francarboxaldehyde and 2-hydroxy-3-francarboxaldehyde).

[0102] NASA's carbon dioxide conversion challenge The CO2 Conversion Challenge is a $1 million NASA-funded competition to convert carbon dioxide into sugars such as glucose, particularly as a process to create mission-critical resources for future Mars missions. Such technologies, by using waste and atmospheric carbon dioxide as resources, are not only applicable to Earth but also enable the manufacture of products using locally sourced resources on Mars.

[0103] On Earth, plants convert CO2 into carbohydrates and oxygen, providing food and breathable air. While there are no plants on Mars, CO2 is abundant. As astronauts begin exploring Mars, they will need to use local resources to free up launch cargo space for other mission-critical supplies. Therefore, NASA is exploring novel ways to convert CO2 into useful compounds such as sugars, which will be key to supplying human explorers on long-term missions to Mars.

[0104] Phase 2 of NASA's CO2 Conversion Challenge has just begun, with the aim of building a system that demonstrates the conversion of CO2 without the use of plants, by combining it with hydrogen to produce simple sugars such as glucose. The selective and efficient co-catalyst technology described herein offers one solution that meets the requirements of the CO2 Conversion Challenge. [Industrial applicability]

[0105] Electrocatalysts for the direct reduction of CO2 to hydrocarbons can be realized via flow electrolytic cells of a similar type to chlor-alkali generation cells currently used on an industrial scale. The CO2 source can be a point source such as a power plant, cement plant, or similar large-scale CO2-emitting industry, or it can be directly extracted from the atmosphere. x P y The phase is applied as nanoparticles or fine particles (5-5000 nm) on a conductive substrate electrode. The particles can be immobilized using one or more polymers, with or without chemical bonding groups for proton or CO2 coordination. This polymer may be of the same type as the support film that guides ions from anode to cathode. Electrolysis can be carried out at near-neutral pH using a carbonate, phosphate, KCl, or sulfate electrolyte.

[0106] Ni of the present invention x P y Together with a co-catalyst system, this technology has the potential to be a direct substitute for fossil fuels (crude oil, coal, natural gas) as a source of chemical feedstocks and energy storage. The carbon-neutral synthetic fuels obtained from this technology do not require the expensive and environmentally impactful fossil fuel supply chain (excavation / drilling, pipelines / tankers, refineries). The fuel can be produced at strategic locations near hubs, as needed. The carbon chemical feedstocks can be tailor-made and are not the result of inefficient processing of raw fossil materials.

[0107] Without further detail, those skilled in the art will likely be able to make the most of the present invention using the description above. Furthermore, although the present invention has been described in relation to the specific embodiments and examples described above, it should be understood that other embodiments utilizing the concepts of the present invention are possible without departing from the scope of the invention and are within the scope of the art of those skilled in the art. Accordingly, the preferred specific embodiments described above should be interpreted as merely illustrative and not in any way limiting the present disclosure.

Claims

1. A cathode for the direct electrochemical reduction of carbon dioxide and / or carbon monoxide to oxygenated hydrocarbon products, The cathode comprises a conductive support substrate and an electrocatalytic coating. The electrocatalyst coating contains Ni ｘ P ｙ nanoparticles, where x and y are such that the compound is Ni ３ P, Ni ５ P ２ Ni １２ P ５ Ni ２ P, Ni ５ P ４ NiP ２ and NiP ３ selected from the group consisting of; or the electrocatalyst coating containing Ni ｘ P ｙ nanoparticles is Ni ３ P, Ni ５ P ２ Ni １２ P ５ Ni ２ P, Ni ５ P ４ NiP ２ and NiP ３ selected from the group consisting of, and further alloyed with Fe ２ P, and the alloy has a Ni - P:Fe ２ P ratio of 99:1 to 1:99 by weight; The conductive support substrate includes hydrophobic and hydrophilic regions to assist in the adsorption of carbon dioxide and / or carbon monoxide from a gaseous or aqueous phase and to achieve separation from water molecules, wherein at least a portion of the nanoparticles in the electrocatalytic coating are located in the hydrophobic region of the conductive support substrate and catalytically interact with carbon dioxide and / or carbon monoxide by electroreduction to produce oxygenated hydrocarbon products, such as cathodes; and A combination of a co-catalyst for the reduction of carbon dioxide and / or carbon monoxide, other than nickel phosphide, arranged to act together with the electrocatalytic coating, The co-catalyst comprises an acid selected from Lewis acids or Bronsted-Lowry acid, wherein the acid is selected from the group consisting of Zn + 2, Fe + 2, Fe 3 +, Ca 2 +, Mg 2 +, Al + 3, AlO +, Si 4 +, SiO 2 +, H 3 BO 3, B(OH) 2 (OR), B(OH) (OR) 2, and mixtures of two or more thereof, and R = alkyl, aryl, arylalkyl, heteroaryl, and heteroarylalkyl, and the heteroatoms of heteroaryl and heteroarylalkyl are selected from nitrogen, oxygen, and sulfur.

2. The combination according to Claim 1, wherein the electrocatalytic coating containing Ni x P y nanoparticles is selected from the group consisting of Ni 3 P, Ni 12 P 5, Ni 2 P, Ni 5 P 4, and Ni P 2.

3. The combination according to claim 1, wherein the electrocatalytic coating containing Ni x P y nanoparticles is selected from the group consisting of Ni 2 P and NiP 2.

4. The combination according to claim 1, wherein the electrocatalytic coating containing Ni x P y nanoparticles is Ni 2 P.

5. The combination according to any one of claims 1 to 4, wherein the acid is an acid selected from the group consisting of Zn + 2, Ca 2+, Mg 2+, H 3 BO 3, B(OH) 2 (OR), B(OH) (OR) 2, and mixtures of two or more thereof, and R = alkyl, aryl, arylalkyl, heteroaryl, and heteroarylalkyl, and the heteroatom of the heteroaryl and heteroarylalkyl is selected from nitrogen, oxygen, and sulfur.

6. The combination according to any one of claims 1 to 4, wherein the acid is an acid selected from the group consisting of Mg²⁺, H₃BO₃, B(OH)₂(OR), B(OH)(OR)₂, and two or more mixtures thereof, and R = alkyl, aryl, arylalkyl, heteroaryl, and heteroarylalkyl, and the heteroatom of the heteroaryl and heteroarylalkyl is selected from nitrogen, oxygen, and sulfur.

7. The combination according to any one of claims 1 to 4, wherein the acid is an acid selected from the group consisting of Mg²⁺ and H₃BO₃.

8. A cathode for the direct electrochemical reduction of carbon dioxide and / or carbon monoxide to oxygenated hydrocarbon products, The cathode comprises a conductive support substrate and an electrocatalytic coating. The electrocatalytic coating comprises nanoparticles of Ni x P y, where x and y are integers such that the compound is selected from the group consisting of Ni 3 P, Ni 5 P 2, Ni 12 P 5, Ni 2 P, Ni 5 P 4, Ni P 2, and Ni P 3; or the electrocatalytic coating comprising nanoparticles of Ni x P y is further alloyed with Fe 2 P, selected from the group consisting of Ni 3 P, Ni 5 P 2, Ni 12 P 5, Ni 2 P, Ni 5 P 4, Ni P 2, and Ni P 3, and the alloy has a Ni-P:Fe 2 P ratio of 99:1 to 1:99 wt%; The conductive support substrate includes hydrophobic and hydrophilic regions to assist in the adsorption of carbon dioxide and / or carbon monoxide from a gaseous or aqueous phase and to achieve separation from water molecules, wherein at least a portion of the nanoparticles in the electrocatalytic coating are located in the hydrophobic region of the conductive support substrate and catalytically interact with carbon dioxide and / or carbon monoxide by electroreduction to produce oxygenated hydrocarbon products, such as cathodes; and A combination of a co-catalyst for the reduction of carbon dioxide and / or carbon monoxide, other than nickel phosphide, arranged to act together with the electrocatalytic coating, The co-catalyst comprises a base selected from Lewis bases or Bronsted-Lowry bases, and the base is selected from the group consisting of NH3, carbamide, urea, hydrazine, primary amines, secondary amines, tertiary amines, pyridine, and mixtures of two or more thereof.

9. The combination according to claim 8, wherein the electrocatalytic coating containing Ni x P y nanoparticles is selected from the group consisting of Ni 3 P, Ni 12 P 5, Ni 2 P, Ni 5 P 4, and Ni P 2.

10. The combination according to claim 8, wherein the electrocatalytic coating containing Ni x P y nanoparticles is selected from the group consisting of Ni 2 P and NiP 2.

11. The combination according to claim 8, wherein the electrocatalytic coating containing Ni x P y nanoparticles is Ni 2 P.

12. The combination according to any one of claims 8 to 11, wherein the co-catalyst is a base selected from the group consisting of NH3, primary amines, secondary amines, and tertiary amines.

13. The combination according to any one of claims 8 to 11, wherein the co-catalyst is a tertiary amine.

14. The combination according to any one of claims 8 to 11, wherein the co-catalyst is hexamethylenetetramine.

15. A cathode for the direct electrochemical reduction of carbon dioxide and / or carbon monoxide to oxygenated hydrocarbon products, The cathode comprises a conductive support substrate and an electrocatalytic coating. The electrocatalytic coating comprises nanoparticles of Ni x P y, where x and y are integers such that the compound is selected from the group consisting of Ni 3 P, Ni 5 P 2, Ni 12 P 5, Ni 2 P, Ni 5 P 4, Ni P 2, and Ni P 3; or the electrocatalytic coating comprising nanoparticles of Ni x P y is further alloyed with Fe 2 P, selected from the group consisting of Ni 3 P, Ni 5 P 2, Ni 12 P 5, Ni 2 P, Ni 5 P 4, Ni P 2, and Ni P 3, and the alloy has a Ni-P:Fe 2 P ratio of 99:1 to 1:99 wt%; The conductive support substrate includes hydrophobic and hydrophilic regions to assist in the adsorption of carbon dioxide and / or carbon monoxide from a gaseous or aqueous phase and to achieve separation from water molecules, wherein at least a portion of the nanoparticles in the electrocatalytic coating are located in the hydrophobic region of the conductive support substrate and catalytically interact with carbon dioxide and / or carbon monoxide by electroreduction to produce oxygenated hydrocarbon products, such as cathodes; and A combination of a co-catalyst for the reduction of carbon dioxide and / or carbon monoxide, other than nickel phosphide, arranged to act together with the electrocatalytic coating, The co-catalyst is a combination comprising Cu, Ag, Au, Zn, a mixture of two or more of these, or salts of their oxides, elemental metals, or alloys.

16. The combination according to claim 15, wherein the electrocatalytic coating containing Ni x P y nanoparticles is selected from the group consisting of Ni 3 P, Ni 12 P 5, Ni 2 P, Ni 5 P 4, and Ni P 2.

17. The combination according to claim 15, wherein the electrocatalytic coating containing Ni x P y nanoparticles is selected from the group consisting of Ni 2 P and NiP 2.

18. The combination according to claim 15, wherein the electrocatalytic coating containing Ni x P y nanoparticles is Ni 2 P.

19. The combination according to any one of claims 15 to 18, wherein the co-catalyst comprises a salt of Cu, a simple metal, or an alloy.

20. The combination according to claim 15, wherein the co-catalyst comprises Cu, Ag, Au, Zn, a mixture of two or more thereof, or a soluble salt of an oxide thereof.

21. The combination according to any one of claims 1 to 20, wherein the co-catalyst comprises an ionomer or a conductive polymer.

22. The cathode is in contact with the electrolyte solution containing the co-catalyst, or the co-catalyst is HCO ３ － Or CO ３ ２－ Or H ＋ The combination according to any one of claims 1 to 20, wherein the ionic liquid electrolyte has a transport function and is in contact with the cathode.

23. The combination according to claim 1, wherein the cathode is in contact with an electrolyte solution containing the co-catalyst, and the conductive support substrate further contains the same co-catalyst.

24. The aforementioned co-catalyst is HCO ３ － or CO ３ ２－ or H ＋ A combination according to any one of claims 1 to 20, wherein the ionic liquid has a transport function.

25. The combination according to any one of claims 1 to 20, wherein the conductive support substrate further incorporates a material to be reduced, thereby causing the electrocatalytic coating to catalytically interact with the material to be reduced incorporated into the conductive support substrate.

26. The combination according to claim 25, wherein the material to be reduced includes carbon dioxide, carbon monoxide, or a mixture thereof.

27. The combination according to any one of claims 1 to 20, wherein the conductive support substrate is an ionomer or a conductive polymer.

28. A method for producing oxygenated hydrocarbon products from water, carbon dioxide and / or carbon monoxide via an electrolytic reaction, wherein the method is: (a) A step of placing any one combination of claims 1 to 20 together with an anode in an electrolyte, (b) A step of making the anode and cathode conductive contact with an external current source, (c) A step of providing a source of carbon dioxide and / or carbon monoxide to the cathode, (d) A step of applying an electric current to drive the electrolysis reaction in the cathode, thereby selectively producing oxygenated hydrocarbon products from carbon dioxide and / or carbon monoxide, Methods that include...

29. The method according to claim 28, wherein the electrocatalytic coating and co-catalyst are selected to produce a product selected from the group consisting of 2,3-franzioll, 2-formylfuran-3-ol, ethylene glycol, 1,3-propanediol, 1,2-propanediol, stereoisomers thereof, and combinations thereof.

30. The method according to claim 28 or 29, wherein the carbon dioxide source and / or carbon monoxide source is a flow source.

31. The co-catalyst bonds to the reaction intermediate on the surface of the electrocatalytic coating or in solution. In addition, 1) the bonding orientation of the intermediate affects the bonding orientation and / or 2) surface-bonded hydrides or other CO ２ A combination according to any one of claims 1 to 20, which involves: / activating the intermediate for a subsequent reaction with the CO reaction intermediate, and / or 3) affecting the bond strength of the intermediate to make it stronger or weaker, and / or 4) promoting the formation of a new reaction intermediate on the surface.

32. The combination according to claim 15, wherein the co-catalyst comprises a metal selected from the group consisting of Cu, Ag, Au, Zn, and intermetallic compounds thereof.

33. The combination according to claim 32, wherein the co-catalyst metal or intermetallic compound is in the form of nanoparticles.

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