Docket No.070439.01870 ELECTROREDUCTION OF CARBON DIOXIDE (CO2) TO MULTI-CARBON PRODUCTS ON ELECTROCATALYST COMPRISED OF MOLYBDENUM DIPHOSPHIDE (MoP2) AND ITS DOPED DERIVATIVES STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT [0001] This invention was made with government support under DE-FOA-0002145 awarded by the Department of Energy. The government has certain rights in the invention. CROSS-REFERENCE TO RELATED APPLICATION [0002] The present application claims priority to U.S. Provisional Application No.63/567,121, filed March 19, 2024. The entire contents of this application are hereby incorporated by reference in its entirety. TECHNICAL FIELD [0003] The present disclosure relates to a novel application of the molybdenum diphosphide (MoP2) compound that serves as an electrocatalyst for the direct electrochemical reduction of carbon dioxide and/or carbon monoxide to hydrocarbons, carbohydrates, and other useful products, collectively referred to below as oxygenated hydrocarbons (or oxyhydrocarbons). BACKGROUND [0004] The adoption of CO2 electrolysis that uses renewable electricity could accelerate the transition to power generation systems and chemical production that consumes carbon from the atmosphere, thus achieving net-negative emissions. CO2 electrolysis to multi-carbon products can potentially replace petrochemical feedstocks and fuels, while consuming emitted CO2 from industrial processes and taking CO2 from the atmosphere. However, the large-scale industrial implementation of this technology is not on the horizon without major technical advances in materials availability, catalyst efficiency, selectivity and durability. The large-scale adoption of this technology is considered an indispensable need for the realistic reduction of global CO2 emissions that are the root cause of climate change. The frightening climate events that we are experiencing now globally are undeniable proof of petrochemical poisoning caused by over consumption of buried fossil reserves and unregulated emissions to Earth ecosystems on land, sea and atmosphere. 1 168858578.1
Docket No.070439.01870 [0005] The intermittent nature of most renewable energy sources (e.g. solar and wind) entails a need for energy storage. Energy can be stored safely and conveniently as chemical bonds. Methane reduced from CO2 is one such possible energy carrier. This energy carrier could then be introduced in a closed loop cycle, with recovery of the spent carrier (CO2) from the atmosphere making the technology carbon neutral—provided a renewable energy source such as sunlight or wind is used to drive the process. Furthermore, the recent utilization of fossil natural gas resources in the US has spurred a large investment in industries relying on cheap natural gas. Renewable methane production from captured CO2 reduction in these so-called “greener” industries would support a sustainable industry beyond the lifetime of the current natural gas resources and thus gradually increase the market for these new technologies in other industries. [0006] Electrochemical CO2 reduction reactions (Direct CO2 Reduction Reaction, DCRR) have been realized to alcohols on noble metals, and to alkanes on Cu. These technologies are still severely limited from attaining significant impact by at least the following: significant H2 co- production (by-product), low selectivity for a single alkane/alkene product, limited tunability of selectivity to other desired products, and the high cost of noble metals for the anodes and other materials such as membrane separators. Of further complication, a small 110 mV thermodynamic difference separates CO2 reduction to CO (a key intermediate) vs. proton reduction to H2 (Eqs 1 and 2). Copper cathodes catalyze this reaction at lower potentials, i.e., higher efficiencies than any previous pure metal electrode, but at low selectivity as other DCRR products form from the CO intermediate. This poor selectivity stems for the nature of the electron transfer process that generates CO. Unlike copper and other simple metals, electrocatalysts comprised of transition metal phosphides (TMPs) have been shown to operate via hydride transfer with the production of formic acid as the first precursor to making multi-carbon products and is the subject of our earlier patent (US-20230193481-A1; US-10676833-B2). H2 production from water (HER) occurs on both types of catalysts as a competing reaction that lowers the efficiency of CO2 conversion. Controlling the branching between CO and HCOOH production vs sacrificial HER production is key to achieving selective DCRR catalysis. Thus, improved and more efficient DCRR catalysts are eagerly sought. This is precisely what this patent application addresses. [0007] Molybdenum diphosphide (MoP2) is a compound that serves as an electrocatalyst for the direct electrochemical reduction of CO2 and/or CO to hydrocarbons, carbohydrates, and 2 168858578.1
Docket No.070439.01870 other useful DCRR products. MoP2 is a stoichiometric compound that has structural, physical, and chemical properties that are distinct from any other molybdenum phosphide compounds, notably molybdenum monophosphide (MoP). As an electrocatalyst, MoP2 can convert CO2 to three classes of oxyhydrocarbons: C1: Formic Acid; C2: ethylene oxide and ethylene glycol; and C4: 2,3- furandiol, furan, using hydrogen extracted from water or from molecular H2 in an electrolyzer. [0008] The product selectivity, electrical efficiency, and the catalyst stability (against corrosion or dissolution) during electrolysis can be modified by doping of MoP2 at either the Mo or the P atom sites. Doping can be done using compatible atoms that retain the lattice structure of the crystalline solid, yielding compounds of stoichiometry Mo1-xAxP2 or MoP2-xBx (where A and B refer to dopant atoms at Mo and P sites, respectively). Doping at P can be performed with these group#15 elements (N, Ar, Sb). Doping at Mo can be performed with these transition metal elements (#5d: Ta W, Re; #4d: Y, Zr, Nb; #3d: Ti, V, Cr). Other DCRR products can be produced from MoP2 electrocatalytically if combined with a cocatalyst to steer the product selectivity. Any combination of MoP2 with one or more cocatalysts to perform DCRR is specifically included in this patent application. Examples of the cocatalysts we have tested fall in the same class as those we have previously published and claimed in our patent on nickel phosphides (US-20230193481-A1). SUMMARY [0009] More efficient and selective class of electrocatalysts and methods for DCRR are provided by the present disclosure. [0010] In one Aspect, the disclosure is directed to an electrode comprising a conductive support substrate and an electrocatalyst coating, where the electrocatalyst coating comprises nano- to micro-sized particles of MoxPy, wherein x and y represent integers designating the stoichiometric compounds. In some embodiments, the MoxPy microparticles comprise of two stoichiometric compounds of MoP plus MoP2. In some embodiments, the particles have sizes in the range from about 0.05 ^m to about 3 ^m. In some embodiments, the conductive support, upon which the electrocatalyst is deposited, further incorporates a material to be chemically reduced, whereby the electrocatalyst coating catalytically transforms the material to be reduced 3 168858578.1
Docket No.070439.01870 incorporating it into the conductive support. In some embodiments, the material to be reduced at the cathode comprises carbon dioxide, carbon monoxide, or a mixture thereof. [0011] In some embodiments, the conductive support substrate of the above electrodes comprises hydrophobic regions and hydrophilic regions to aid in adsorption of carbon dioxide and/or carbon monoxide from gas or aqueous phases to achieve separation from water molecules. Wherein, at least some of the electrocatalyst particles are in the hydrophobic regions of the conductive support substrate and catalytically interact with the carbon dioxide and/or carbon monoxide by DCRR to produce oxyhydrocarbon products. In some embodiments, the conductive support is an ionomer, and ionic liquid, or a conducting polymer. [0012] In another aspect, the disclosure is directed to a method for generating oxyhydrocarbon products from water, carbon dioxide, and/or carbon monoxide via an electrolysis reaction, comprising the steps of: (a) placing a cathode according to the present disclosure in an electrolyte together with an anode; (b) placing the anode and the cathode in conductive contact with an external source of electric current; (c) providing a source of carbon dioxide and/or carbon monoxide to the cathode; and (d) applying the electric current to drive an electrolysis reaction at the cathode, wherein oxyhydrocarbon products are generated from the carbon dioxide and/or carbon monoxide. In some embodiments, the generated oxyhydrocarbon product comprises a product selected from the group consisting of acetic acid, acetaldehyde, ethanol, ethylene, ethylene glycol, ethylene oxide, formic acid, 2,3-furandiol, furan, 2-formylfuran-3-ol, 1,3-propanediol, 1,2- propanediol, stereoisomers thereof, and combinations thereof including polymers. [0013] In another aspect, the disclosure is directed to a method for reducing carbon dioxide to oxyhydrocarbon products, comprising: (a) placing a cathode in an electrolyte together with an anode, wherein the cathode comprises a conductive support substrate and an electrocatalyst coating of MoxPy, wherein x and y represent stoichiometric integers of the compounds MoP or MoP2 or mixtures thereof; (b) placing the anode and the cathode in conductive contact with an external source of electric current; (c) providing a source of carbon dioxide to the cathode; and (d) applying the electric current to drive an electrolysis reaction at the cathode that generates electrons at the anode that are delivered to the cathode, wherein an oxyhydrocarbon product is generated from the carbon dioxide, and the electrocatalyst coating is selected so that the oxyhydrocarbon product that 4 168858578.1
Docket No.070439.01870 is generated is selected from the groups consisting of carbohydrates, carboxylic acids, alcohols, aldehydes, ketone, ethers, hydrocarbons and mixtures of two or more thereof. [0014] In another aspect, the disclosure is directed to a method for preparing the MoP2 electrocatalyst for reduction of water, carbon dioxide, or carbon monoxide to oxyhydrocarbon products by a solid state synthesis, the method comprising: (a) preparing a precursor comprising a mixture of a molybdenum source and a phosphorus source; (b) reacting the precursor at a temperature of about 850 0C (increased gradually in increments of 200, starting from 50 and progressing to 250, then 450, followed by 650, and finally reaching 850, with a 3-hour hold time at each step); and (c) heating the precursor for about 24 hours to produce phase-pure MoP2. In some embodiments, the molybdenum source comprises molybdenum oxide (MoO3) or elemental Mo. In some embodiments, hydrogen gas (H2) is included to convert the MoO3 to water plus elemental Mo to serve as reactant for production of MoxPy compounds. In some embodiments, the phosphorus source comprises red phosphorus. In some embodiments, hydrogen gas (H2) is included to convert the red phosphorus to phosphine (PH3) to serve as reactant for production of MoxPy compounds. [0015] In another aspect, the disclosure is directed to a method for preparing MoP2 electrocatalyst for reduction of water, carbon dioxide, or carbon monoxide to oxyhydrocarbon products by a surfactant assisted synthesis, the method comprising: (a) preparing a surfactant solution comprising a surfactant and solvent; (b) adding 1-hexanol to the surfactant solution; (c) dissolving a molybdenum source and a phosphorus source to solution produced from step (b); (d) heating the solution of (c) at a temperature of about 190 oC; and (e) allowing the reaction to proceed for about 24 hours. In some embodiments, the surfactant comprises cetyltrimethylammonium bromide or sodium monododecyl phosphate. In some embodiments, the solvent comprises water and cyclohexane. In some embodiments, the molybdenum source comprises molybdenum(V) chloride or other soluble salt of molybdenum. In some embodiments, the phosphorus source comprises red phosphorus. In some embodiments, the phosphorus source comprises hydrogen phosphite. In some embodiments, the method further comprises washing the MoP2 electrocatalyst with HCl, then ethanol after step (e). 5 168858578.1
Docket No.070439.01870 BRIEF DESCRIPTION OF THE DRAWINGS [0016] FIG.1 is a representative powder X-ray diffraction (PXRD) pattern of synthesized molybdenum monophosphide (MoP). The indices (XYZ) refer to the planes of the hexagonal crystalline phase of MoP as reported in literature. [0017] FIG. 2 is a representative powder Xray diffraction (PXRD) pattern of the synthesized molybdenum diphosphide (MoP2). The indices (XYZ) refer to the planes of the orthorhombic crystalline phase of MoP2 as reported in literature. [0018] FIG. 3 (a) is a Field Emission Scanning Electron Microscopy image (FESEM image) of the synthesized MoP2 particles prepared by the solid-state method. (b) is an Energy Dispersive Spectroscopy of the SEM image from (a) (SEM-EDS image) with table showing the atomic ratios of Mo and P. [0019] FIG. 4 is a representative chronoamperometry measurements under DCRR conditions for MoP2 at three different applied electrical potentials of: 0 V, -0.1 V, and -0.3 V vs RHE reference electrode. [0020] FIG. 5 is a 1H-NMR spectrum of the CO2 reduction products in the catholyte solution following 6 hr electrolysis under DCRR conditions. [0021] FIG. 6 is a 1H-NMR spectrum of the CO2 reduction products in the catholyte solution following 16 hr electrolysis under DCRR conditions. [0022] FIG. 7 (a) are 1H-NMR spectra of the catholyte solutions showing the CO2 reduction products formed by electrolysis at three different applied electrical potentials (0 V, -0.1 V and -0.3 V vs RHE) under standard DCRR conditions. (b) Faradaic efficiencies for each of the CO2 reduction products formed in (a). The remaining Faradaic efficiency (up to 100%) is due to H2 gas production. The data are the average of 3 replicates and the SDs shown. [0023] FIG.8 is a representative 1H-NMR spectrum of the CO2 reduction products using molybdenum monophosphide (MoP) as the electrocatalyst after 6 hr electrolysis and under standard DCCR conditions, with higher loading of Nafion on the catalyst (600µL of ionomer). [0024] FIG.9 is a 1H NMR spectrum, -0.1V vs RHE following KCl addition to the peek cell before electrolysis. Peaks at 3.6, 3.7 confirm chloroethanol formation in the presence of a 6 168858578.1
Docket No.070439.01870 chloride salt. Ethylene oxide reacts readily with chloride salts to form chloroethanol as known from literature. [0025] FIG. 10 is an HPLC spectrum of the catholyte solution: (a) shows the UV data indicating the presence of formic acid at 28 minutes. (b) shows the refractive index (RI) detector data confirming the presence of 2,3-furandiol at 16 mins. [0026] FIG. 11 is an X-ray photoelectron spectrum of de-novo MoP2 and following CO2RR at 16+ hours (600uL of nafion) in the Mo region shows Mo (VI) oxidation states doublet peaks that decrease in intensity over electrocatalysis. Surface XPS of the post-CO2RR shows a relative decrease of the Mo (VI) doublet peaks with a rise in Mo (IV) oxidation peaks corresponding to oxides forming on the surface of the catalyst. [0027] FIG.12 is a 1H-NMR spectrum of reduction products from electro-oxidized MoP2 showing ethylene glycol formation, as well as formation of furan (6.4, 7.5). Molybdenum oxides reduce the 2,3-furandiol to furan and inhibit the conversion of ethylene glycol towards C42,3- furandiol. [0028] FIG.13 is a 1H-NMR spectrum of reduction taken from a long electrolysis (over 22 hours) using MoP2 with higher ionomer loading as the catalyst showing high selectivity towards furandiol as the terminal product. DETAILED DESCRIPTION [0029] The presently disclosed technology is directed to the preparation of oxyhydrocarbons that are common chemical feedstocks from binary Mo-P compounds. [0030] As defined herein, “about” or “approximately,” when used in connection with a numeric value, is intended to include values that are close to, but not exactly, the number. For example, in some embodiments, the term “about” or “approximately” may include values that are within +/- 10 percent of the value. [0031] CO2 reduction may be carried out by direct electrolysis at room temperature, but at least 4 electrons (Reichert, A. M., Chemical Science, 13(37), 11205-11214 (2022)) are needed to form valuable fuels (eqs.2-6). From the listed potentials (Eq 1 to 6), it becomes evident that CO2 reduction occurs in thermodynamic competition with the simpler 2e- hydrogen evolution reaction (HER) in Eq. (1): 7 168858578.1
Docket No.070439.01870 [0032] 2H+ + 2e- → ← H2 (U = 0 V vs RHE at 1 atm. H2) (1) CO2 + H2O + 2e– → ← CO + 2OH– (U = -0.11 V vs. RHE) (2) CO2 + 5H2O + 6e- → ← CH3OH + 6OH- (U = 0.03 V vs RHE) (3) CO2 + 6H2O + 8e– → ← CH4 + 8OH– (U = 0.16 V vs. RHE) (4) 2CO2 + 8H2O +12e– → ← C2H4 + 12OH– (U = 0.07 V vs. RHE) (5) CO2 + H2O + 2e– → ← HCOO– + OH– (U = 0 V vs. RHE) (6) [0033] Therefore, the challenge is to produce an electrocatalyst which preferentially provides hydrogen atom equivalents such as hydrides to reduce CO2 to a specific carbon product rather than forming a mixture of products, H+, or hydrogen gas (H2). For this reason, DCRR has often been performed in neutral pH where the proton concentration at the electrocatalyst surface is low. The present binary compounds and their doped derivatives fall in the class of transition metal phosphides. These form surface hydrides as the active reducing agents, in contrast to conducting metals. [0034] CO2 reduction has been previously demonstrated experimentally on single component transition metal catalysts, with the best selectivity to produce alkanes from CO2 reduction on Cu electrodes occurring in low ionic strength electrolytes (0.1 M KHCO3, pH 6.8). Such results indicate selectivity towards hydrocarbons of 72.3% (CH4 was the major product) achieved at -1.04 V vs. reversible hydrogen electrode (RHE), which is about 1.2 V more negative than the thermodynamic limit of +0.16 V vs RHE (Eq 4). However, such a large over-potential greatly impedes the applicability of this approach for the production of synthetic fuels. Nonetheless, it remains the best performing single component transition metal DCRR electrocatalyst to date. Over-potential at the anode reaction and electrolyte resistance will further contribute to the system power inefficiency. [0035] A viable technology to produce fuels from CO2 must quantitatively compare to industrial processes. Currently, industrial methanol production from CO is estimated at 51% energy efficiency. The theoretical maximum energy efficiency for DCRR to methanol, assuming 0 V over-potential (Eq 3) and complete recovery of products, is 73%. This indicates that DCRR is a technology theoretically capable of competing with the current industrial standard, if other kinetic over-potentials at the cathode, anode and electrolyte can be reduced. The overall system 8 168858578.1
Docket No.070439.01870 efficiency of electrochemical reduction (also referred to herein as “electroreduction”) of CO2 to CH4 is currently 13% on Cu surfaces assuming oxygen evolution is the anode reaction. [0036] The replacement of catalysts (electrodes) is expensive in terms of down-time for any commercial processes, hence it is critical to maintain extended lifetimes of excellent electrocatalyst performance. Industrial applications require significantly longer stabilities than research projects. For example, industrial anodes for the chlor-alkali process (based on RuOx and IrOx) have lifetimes of about 7 years. [0037] Examples of the PXRD characterization of the synthesized MoP and MoP2 crystalline compounds produced as nano-particles through micron size particles is shown in FIGS. 1-3. Highly compacted crystalline powders of MoP and MoP2 have been pressed at 10 ton/inch2 pressures with or without additives as described below to make planar electrodes forming approximately flat surfaces for the inventive family of direct CO2 reduction reaction (DCRR) catalysts. This allows the observation of catalytic activity on a stable surface, and directly comparable to Cu-foils of the prior art. Their activity as DCRR catalysts is shown in the data below (FIGS.4-8). The selectivity of these electrocatalysts for DCRR was found to be tunable based on composition, additive and reaction conditions (including applied potential, pH and solvent) as described below. [0038] Other substrate formats upon which MoP and MoP2 can be deposited for use as electrocatalysts includes any number of conducting materials that can serve as three dimensional electrodes, gas diffusion electrodes and gas diffusion layers. These can be classified as fibers, meshes or porous ceramics. [0039] Further, anion exchange membranes allow for the transport of (H)CO3 2- and neutral CO2(aq) and H2O to the electrocatalyst surface, while restricting H+
due to charge repulsion. DCRR activity is known to be sensitive to pH in that higher pH improves selectivity but limits CO2 availability. Thus, locally restricting proton availability by using an anion exchange membrane, rather than increasing the pH of bulk solution, strongly favors DCCR over HER. Therefore, some embodiments, the present disclosure is directed to a composite electrode of an inventive binary electrocatalyst and various polymers with anion conduction properties near the electrocatalyst surface. Such composites show a significantly improved selectivity for DCRR. 9 168858578.1
Docket No.070439.01870 [0040] Further, some ionic liquids (IL) additives can suppress HER activity in favor of DCRR activity. When combined with the electrocatalyst they can bind protons arriving from the anode, thereby suppressing HER in favor of DCRR performance of the inventive catalysts. Additionally, adventitious choice of the anion of the ionic liquid is known to have a pronounced effect on the CO2 solubility in the IL, so that ionic liquids having high CO2 solubility can be selected as additives to the inventive binary catalysts. This includes examples of guanidinium and imidazolium cations with bicarbonate and carbonate. RESULTS [0041] Some data for two molybdenum phosphides with different structures (MoP and MoP2) are shown in FIG. 1 and FIG. 2. FIG. 1 shows a representative powder Xray diffraction (PXRD) pattern of synthesized molybdenum monophosphide (MoP) prepared using the solid-state synthesis method, which agrees with the reported reference pattern. The PXRD data shows that MoP comprises a hexagonal crystal system with Mo-P bond length of about 2.45 Å. FIG.2 shows a representative PXRD pattern of the synthesized molybdenum diphosphide (MoP2) prepared using the solid-state synthesis method, which agrees with the reported reference pattern. All peaks in the obtained pattern were indexed to the standard XRD profiles (JCPDS #16-0499), and no impurities were detected. The MoP2 comprises an orthorhombic crystal system Cmc21 with Mo-P bond length ranging from about 2.48 Å to about 2.51 Å. [0042] The different crystalline structures can be expected to offer varying degrees of electrocatalytic activities resulting from different active sites and surface area where reaction takes place. For this reason, we have used alternative synthesis methods to achieve higher surface-to- volume ratios while retaining the phase purity (see Examples 5, 6 and 7, below). [0043] The morphology of the samples was characterized by Field Emission Scanning Electron Microscopy image (FESEM image) of the as-synthesized MoP2 particles prepared by the solid-state method is shown in FIG. 3(a). The particle morphology is composed of aggregated smaller particles, and exhibits uniform distribution within the size range of 0.5-2^m. FIG. 3(c) shows the Energy Dispersive Spectroscopy of the SEM image from (a) (SEM-EDS image) while the inserted table gives the atomic ratios of Mo and P. SEM-EDS revealed an atomic ratio of Mo:P approximately 1:2.28, indicating that the synthesized MoP2 is close to its stoichiometric composition, albeit with a slightly phosphorus-rich surface layer, as commonly seen in this family. 10 168858578.1
Docket No.070439.01870 [0044] FIG. 4 shows representative chronoamperometry measurements using MoP2 as cathode measured under standard DCRR conditions (CO2 gas at 5 sccm flow rate; electrolyte is 0.5 M KHCO3) at three different applied electrical potentials of: 0 V, -0.1 V, and -0.3 V vs RHE reference electrode. These data show that an induction current occurs at each potential prior to reaching a steady-state current that is stable and proportional to the applied voltage. The observed steady-state current is created in the presence of CO2 gas in the electrolyzer that reacts at the biased cathode to create the observed DCRR products. The standard cathode comprises a conductive substrate (Al or Ti mesh) onto which the MoP2 microparticles are suspended using Nafion as binder and subsequently pressed into a solid pellet at 10 tons/inch2 pressure. Only MoP2 and Nafion are exposed to the electrolyte during electrolysis. [0045] 1H-NMR of the CO2 reduction products produced in the cathode compartment of the electrolyzer, using MoP2 electrocatalyst under standard DCRR conditions at 6 hr reaction time (FIG. 5). The data demonstrate the formation of two oxyhydrocarbon products, 2,3-furandiol (singlets at 7.2 ppm and 6.1 ppm) and ethylene oxide (singlet at 2.7 ppm). Definitive identification was further confirmed by addition of commercially sourced ethylene oxide to the catholyte to verify the peak position. An NMR peak corresponding to formic acid (8.4 ppm) is not visible in this figure but does form in low yield in many other trials. We note that formic acid is the initial product of CO2 reduction on MoP2 and is the precursor that is converted to the observed products. [0046] FIG.6 shows that if the reaction time is increased to 16 hr and the same cathode is used, an additional oxyhydrocarbon product (ethylene glycol, singlet peak at 3.58 ppm) is produced. These studies and others show that the peak at 3.58 ppm for ethylene glycol is produced by hydrolysis of the initial ethylene oxide product (2. 7 ppm) which is catalyzed by the KHCO3 electrolyte. Definitive identification was further confirmed by addition of commercially sourced ethylene glycol to the catholyte to verify the peak position. [0047] The foregoing conclusions were further corroborated by measurements at other applied potentials. FIG. 7(a) shows the 1H NMR spectra of the catholyte solutions after 6 hr electrolysis at three different applied electrical potentials (0 V, -0.1 V and -0.3 V vs RHE) under standard DCRR conditions. This figure shows that the applied potential changes the relative yield of the three CO2 reduction products. FIG. 7(b) is a bar graph plotting the average Faradaic efficiencies (yields) of each of the three CO2 reduction products formed in FIG.7(a) taken as the 11 168858578.1
Docket No.070439.01870 average of three replicates. The remaining Faradaic efficiency (up to 100%) is due to the production of H2 gas from water. These yields are limited by the delivery rate of CO2 to the cathode. [0048] FIG. 8 shows the corresponding 1H-NMR spectrum of the catholyte products formed when using molybdenum monophosphide (MoP) as the electrocatalyst. MoP produces the same CO2 reduction products but a lower overall yield as revealed by the peak intensities. This indicates that, for this family of binary compounds (MoP vs MoP2) where the crystalline phases differ but the same elements are present, there is a clear difference in the amount of CO2 products that form. This can be attributed to the different CO2 adsorption affinity and CO2 reactivity with the catalysts and the competition with H2 production from water. These data shows that MoP2 is a much more effective catalyst at producing oxyhydrocarbon than MoP. [0049] Based on the foregoing results, this family of DCRR binary catalysts shows a structure dependent activity for CO2 reduction. Understanding this structure dependence allows for the rational design of new CO2 reduction electrocatalysts. This knowledge enables us to explain the trend in the rate of total DCRR product formation on various electrocatalysts, notably Fe2P, Ni2P and NiP2 from our previously published works covered under patents (US-20230193481-A1; US-10676833-B2), Neither MoP or MoP2 produces CO as gaseous product under DCRR conditions, which we conclude is due to the absence of CO formation. The DCRR current density is stable over at least 16 hr with no sign of degradation. This suggests that CO does not accumulate on the surface, as this would eventually block all sites and eliminate/lower the current. This characteristic is common to all TMP compounds we have investigated as DCRR electrocatalysts thus far and defines their classification as hydride transfer catalysts (US-20230193481-A1; US- 10676833-B2) in contrast to electron transfer catalysts. [0050] As an additional strategy to improve activity further, the HER activity of the inventive binary catalysts can be reduced in favor of the DCRR activity by incorporating polymers and/or ionic liquids (Guerra, O. J., Joule, 7(6), 1111-1133 (2023)) with low H+ conductivity but good CO2 and H2O transport properties. The polymers such as PTFE (TEFLON™) and/or ILs such as N-alkylated imidazolium cations can be directly mixed in with the electrocatalyst particles to offer a composite heterogeneous electrode. 12 168858578.1
Docket No.070439.01870 [0051] In one aspect, the disclosure is directed to a cathode comprising a conductive support substrate underlying the electrocatalyst coating, the electrocatalyst coating comprising microparticles of MoxPy, where x and y represent integers such that the compounds comprise MoP and MoP2, or a combination thereof. In some embodiments, the electrocatalyst microparticles have sizes in the range from about 0.5 ^m to about 3 ^m. In some embodiments, the particles range in size from about 0.0.5 ^m to about 1 ^m. These different particles sizes arise from different synthesis methods. [0052] In some embodiments, the conductive support substrate further incorporates a material to be reduced, whereby the electrocatalyst coating catalytically interacts with the material to be reduced incorporated into the conductive support substrate. In some embodiments, the cathode material to be reduced comprises carbon dioxide, carbon monoxide, or a mixture thereof. Alternatively, the conductive support may be an ionomer or a conducting polymer. [0053] In some embodiments, the conductive support substrate of the above cathodes comprises hydrophobic regions and hydrophilic regions to aid in adsorption of carbon dioxide and/or carbon monoxide from gas or aqueous phase to achieve separation from water molecules, wherein at least some of the electrocatalyst microparticles are in the hydrophobic regions of the conductive support substrate and catalytically interact with the carbon dioxide and/or carbon monoxide by electrical reduction to produce oxyhydrocarbon products. The oxyhydrocarbon product can be a mixture of hydroxylated hydrocarbons, aldehydes, ketones, carboxylates, or a single member of these families (such as methanol, ethanol, butanol, etc.). In some embodiments, the oxyhydrocrbon products may comprise formic acid, ethylene glycol, 2,3-furandiol, ethylene oxide, 2-formylfuran-3-ol, 1,3-propanediol, 1,2-propanediol, stereoisomers thereof, or combinations thereof. Further, the oxyhydrocarbon product can be a mixture of the above products. [0054] In a further aspect, the disclosure is directed to a method for reducing carbon dioxide to oxyhydrocarbon products, comprising: (a) placing a cathode in an electrolyte together with an anode, wherein the cathode comprises a conductive support substrate and an electrocatalyst coating, wherein the electrocatalyst coating comprising microparticles of MoxPy, wherein x and y represent integers such that the compounds comprise MoP or MoP2; (b) placing the anode and the cathode in conductive contact with an external source of electric current; (c) providing a source of carbon dioxide to the cathode; and (d) applying the electric current to drive an electrolysis reaction 13 168858578.1
Docket No.070439.01870 at the cathode that generates electrons at the anode that are delivered to the cathode, wherein an oxyhydrocarbon product is generated from the carbon dioxide, and the electrocatalyst coating is selected so that the oxyhydrocarbon product that is generated is selected from the group consisting of carbohydrates, carboxylic acids, aldehydes, ketone, and mixtures of two or more thereof. [0055] In another aspect, the disclosure is directed to a method for preparing MoP2 by solid state synthesis for use in electrocatalytic reduction of water, carbon dioxide, or carbon monoxide to oxyhydrocarbon products, the method comprising: (a) preparing a precursor comprising a mixture of a molybdenum source and a phosphorus source; (b) reacting the precursor at a temperature of about 850 0C (increased gradually in increments of 200, starting from 50 and progressing to 250, then 450, followed by 650, and finally reaching 850, with a 3-hour hold time at each step); and (c) heating the precursor for about 24 hours to produce MoP2 electrocatalyst. In some embodiments, the molybdenum source comprises MoO3 or elemental Mo. In some embodiments, the phosphorus source comprises red phosphorus, and, in some embodiments, further comprising prior to step (b), the precursor is heated to about 60 oC for about 10 minutes. [0056] In another aspect, the disclosure is directed to a method for preparing MoP2 by surfactant assisted synthesis for use as electrocatalyst for reduction of water, carbon dioxide, or carbon monoxide to oxyhydrocarbon products, the method comprising: (a) preparing a surfactant solution comprising a surfactant and solvent; (b) adding 1-hexanol to the surfactant solution; (c) dissolving a molybdenum source and a phosphorus source to solution produced from step (b); (d) heating the solution of (c) at a temperature of about 190 °C; and (e) allowing the reaction to proceed for about 24 hours. In some embodiments, the surfactant comprises cetyltrimethylammonium bromide or monododecyl phosphate. In some embodiments, the solvent comprises water and cyclohexane. In some embodiments, the molybdenum source comprises molybdenum(V) chloride. In some embodiments, the phosphorus source comprises red phosphorus. In some embodiments, the method further comprises washing the MoP2 electrocatalyst with HCl, then ethanol after step (e). [0057] The catalysts can be used in conjunction with a titanium film electrode, for example, by being pressed into a pellet and bonded to a titanium film electrode via silver paint and sealed in a non-conducting epoxy. Alternatively, the catalysts can be supported on carbon or ceramic powder. 14 168858578.1
Docket No.070439.01870 SUPPORT SUBSTRATES [0058] In one embodiment, the electrocatalyst comprises a catalytic group and a conductive support substrate supporting a plurality of the catalytic groups. In some embodiments, the support substrate is capable of incorporating hydrogen cations, and at least some of the catalytic groups supported by the support substrate are able to catalytically interact with the hydrogen cations incorporated into the support substrate. In some embodiments, the supporting substrate is capable of incorporating water molecules, and at least some of the catalytic groups supported by the support substrate are able to catalytically interact with water molecules incorporated into the support substrate. In some embodiments, the support substrate is capable of incorporating carbon dioxide, and at least some of the catalytic groups supported by the support substrate are able to catalytically interact with CO2 molecules incorporated into the support substrate. [0059] The support substrate has a plurality of porous regions that are microporous, mesoporous, and/or macroporous. In some embodiments, the support substrate is a microporous substrate having an average pore size of less than about 2 nm. In some embodiments, the support substrate is a mesoporous substrate having an average pore size of from about 2 to about 50 nm. In some embodiments, the support substrate is a macro-porous substrate having an average particle size of greater than about 50 nm. [0060] The support substrate is conductive to electrons so that when an electric potential difference is present across separate points on the support substrate, the mobile charges within the support substrate are forced to move, and an electric current is generated between those points. In some embodiments, the support substrate is rendered 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 foils/wires/meshes/foams/knotted wire meshes, aluminum foils/wires/meshes/foams/knitted wire meshes, fluoride-doped tin oxide (FTO or (F- SnO2) coated glass and indium tin oxide (ITO) (or any of the transparent conductive oxides) coated glass, and multilayer structures having nano-structured semiconductor films coated onto the conductive substrates. Other means of causing the support substrate to be conductive are within the scope of the disclosure. For example, in some embodiments, the support substrate contacts a sensitized semiconductor. 15 168858578.1
Docket No.070439.01870 [0061] Preferably, the support substrate has hydrophobic regions and hydrophilic regions. In some embodiments, the reduction of water or CO2, while not wishing to be limited by theory, it is thought that at least some of the catalytic groups can be supported in the hydrophobic regions of the support substrate and once supported are able to 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 the catalytic groups which are otherwise insoluble in aqueous solution. [0062] In some embodiments, the hydrophobic regions are formed by a hydrophobic polymeric backbone and the hydrophilic regions are regions of ionizable functional groups, preferably on the polymer backbone that can serve as sites for proton conductance. Preferably the ionizable functional groups are sulfonate groups (–SO3H) that lose a proton to form negatively charged sulfonate groups. Alternatively, the ionizable functional groups can form positively charged functional groups that can serve as sites for hydroxide or carbonate ion conductance, if preferred. [0063] The supporting substrate can be, for example, polysulfones, polysulfonates, and polyphosphonates. In some embodiments, the supports substrate comprises a sulfonated fluoro- polymer (sold under the trademark of NAFION®). The hydrophobic CF2CF(CF3)O– polymer backbone of NAFION® forms a hydrophobic solid that is penetrated by aqueous channels lined with the hydrophilic ionizable sulfonic acid groups. Investigations into the sub-structure of NAFION® coatings on solid surfaces have revealed that the polymer layers contain these hydrophilic channels throughout the otherwise hydrophobic regions of the membrane. These channels allow the diffusion of small molecules such as water. [0064] Other supporting substrates that can be used include, for example, perfluorinated sulfonic acid polymer cation-exchange membranes such as F-14100, F-930 and F-950, the GEFC perfluorinated proton exchange membranes, polysulfone ionomers, nanostructured films formed by metal oxide nanoparticles suitably decorated with organic acids including perfluorinated sulfonic acids, nanostructured films formed by the hydrolysis of alkoxysilanes suitably decorated with organic acids including perfluorinated sulfonic acids. [0065] Other supporting substrates can be, for example, polyfluorinated alkaline exchange membranes (AEM) that rely upon fixed cationic functional groups within the polymer to prevent 16 168858578.1
Docket No.070439.01870 the conduction of protons and allow conduction of mobile anions for conductivity. Examples of commercial AEMs include Tokuyama® AEM. Also, within the scope are heterogeneous- homogeneous colloidal systems, two-phase mixtures (stabilized and unstabilized with surfactant), conducting polymers (e.g., poly(3,4-ethylenedioxythiophene) (PEDOT)), surface-modified silica and titania. [0066] Any means of contacting the electrocatalyst with water. CO2 or carbonate mineral is within the scope of the disclosure. In some embodiments, the electrocatalyst is immersed in a solution containing water molecules. In some embodiments, the solution is an aqueous solution containing electrolyte. In some embodiments, the aqueous solution is a solution from which water is preferentially removed (i.e., solid liquid separation). For example, when the aqueous solution is salt water or sea water the water could be removed leaving the salt behind (i.e., desalination). In some embodiments, about 0.5 M electrolyte is sufficient. [0067] The following examples are provided to further illustrate the methods and compositions of the present disclosure. These examples are illustrative only and are not intended to limit the scope of the disclosure in any way. EXAMPLES Example 1. Electrode Fabrication [0068] 200 mg of electrocatalyst powder was suspended in 50 µL of 5% NAFION® suspension previously neutralized with NaOH. The electrocatalyst powder was continuously mixed with the NAFION® suspension by mortar and pestle until dried. To fully dry these they were further dried under vacuum for several hours. [0069] 200 mg of the resulting electrocatalyst/polymer composite was pressed under 10 tons of pressure in a die. The resulting pellet was mounted on a Ti plate (Sigma-Aldrich) with a drop of Ag-paint (SPI supplies). The Ti plate was previously fixed to a copper wire with Ag-paint. The copper wire assembly was threaded through a glass tube. After drying, the Ag-paint, the sides of the electrocatalyst pellet, and Ti plate was isolated from solution by covering in Hysol™ T1 epoxy (Logitech) all the way up onto the glass tube. The geometric surface area was determined by imaging the exposed surface and measuring it using the ImageJ™ software. 17 168858578.1
Docket No.070439.01870 Example 2. Electrochemical Measurement [0070] All solutions were prepared using Millipore water. Electrochemical cells were cleaned using piranha solution (1:335% H2O2 and concentrated H2SO4) followed by thorough rinsing in Millipore water. A three-electrode setup with a NAFION® membrane or anion- exchange membrane separator between working and counter compartment was used for all the electrochemical measurements. To avoid the possibility of Pt contamination a B-doped diamond electrode was used as a counter electrode during durability measurements. A homemade Hg/HgSO4 (Sat’d KCl) reference electrode was used and calibrated against a commercial Saturated Calomel electrode at open circuit potential prior to each measurement. Chronoamperiometric data was not corrected for uncompensated IR-drop, as only small currents on the order of hundreds of microamperes were drawn, effectively removing this source of error. [0071] Electrolytes were prepared from Millipore water using high purity grade reagents. Furthermore, as a further precaution to remove potential metal impurities solutions were filtered through K+-Chelex 100 matrix. Electrolytes were stored in Piranha-cleaned flasks until used. Just prior to measurements the electrolytes were saturated with CO2 (Airgas CD1200) cleaned using a Supelco hydrocarbon trap (Sigma) to < 6ppm CH4 (the major hydrocarbon impurity). [0072] Product analyses were conducted on a HP5890 Series II GC with a 5A MSieve (Restek) 0.53mm capillary column using Ar carrier gas (cleaned for hydrocarbons and moisture on a Supelco Hydrocarbon, moisture trap). Calibrations were performed using certified mixed gasses i.e., 1.04% CH4/Ar from Airgas, 1.02% H2/Ar, and pure C2H4 likewise from Airgas. Example 3. MoP2 microparticles via solid state synthesis (SSS) [0073] 2.5 mol% stoichiometric excess of red phosphorous (0.4 g) (Alfa-Aesar 99%) and stoichiometric amounts (0.6 g) of elemental Mo (Sigma-Aldrich <150 µm) were thoroughly mixed in a mortar, transferred to a quartz tube, evacuated and sealed after cleaning with Ar by back filling 2-3 times. The evacuated tubes were placed in a furnace and ramped to 850 °C and kept there for 24 hours. Ramp rates were modest to avoid over heating during reaction. Temperatures were ramped from 50°C to 250 °C over 200 min with a 180 min dwell time, then to 450 °C over 200 min with a 180 min dwell time, then to 650 °C over 200 min with a 180 min dwell time, and finally to 850 °C over 200 min with a 24 hour dwell time. Sealed tubes were then cooled to room temperature under ambient conditions. 18 168858578.1
Docket No.070439.01870 Example 4. Synthesis of MoP2 microparticles Using Soft-Templating Synthesis Method Followed by Annealing. Greater surface area within the same binary system will result in improved electrocatalytic turnover frequency resulting in faster product release with better conversion performance. For this reason, we have synthesized the MoP and MoP2 compounds using alternative methods that create higher surface to volume ratios (surface areas). [0074] The catalysts were synthesized using the soft-templating method with surfactants as described in our previous synthesis of nickel phosphides (Dhiman, M., et. al., Journal of Materials Chemistry A, 11(2), 717-725 (2023)). In a typical synthesis, cetyltrimethylammonium bromide (CTAB = 1.5 g) or sodium monododecyl phosphate (SMDP = 1.5 g) was stirred (700 RPM) in water (100 mL) and cyclohexane (100 mL) mixture. After 15 min of stirring, 1-hexanol (10 mL) was added dropwise. The resulting solution was further stirred for 30 min at room temperature followed by addition of molybdenum (V) chloride (7 g Mo2Cl10) and red phosphorus (12 g). The resulting solution was transferred into a Teflon-sealed autoclave reactor and was heated to 190°C for 24 h. After completion of the reaction, the mixture was allowed to cool down to room temperature. The black solid product formed was isolated by centrifugation and unreacted species including surfactant molecules were removed by washing with water (until the supernatant is a clear solution). The isolated product was further washed with 3% HCl to remove the surface phosphate/ oxide species, followed by ethanol wash in the end. The as-synthesized materials were dried at 60 °C for 6 h and termed MoP2-CTAB (-cetyltrimethylammonium bromide) and MoP2- SMDP (-sodium monodecyl phosphate). The as-synthesized powder was then annealed in 1% H2 for 2h at 350oC to impart crystallinity. Example 5. Characterization of MoP and MoP2 Microparticles [0075] PXRD analysis was performed on a Bruker AXS D8 Advance using a Cu Kα X- ray tube (1.546Å), a scan time of 1 hour or 12 hours, and a 2θ range of 15–70° or 10-120°. Samples were analyzed prior to electrochemical testing by dispersing the powder on a glass microscope slide and flattening the powder surface using another glass slide. Electrodes analyzed after electrochemical tests were measured by gently cutting the Ti-foil free from the Pyrex tube and removing the Cu-wire. The electrode-pellet and Ti-foil were placed on a glass slide and the PXRD pattern recorded. FIG.1 shows the PXRD of MoP microparticles are formed in a hexagonal crystal 19 168858578.1
Docket No.070439.01870 lattice, while FIG. 2 shows the PXRD of MoP2 microparticles are formed in an orthorhombic crystal lattice. [0076] HRTEM analysis was performed at 200 keV, vacuum pressure of about 2 x 10-7 Torr, and operated using the standard imaging and diffraction mode. Powder samples from the electrodes were placed on an Au mesh TEM grid (300 mesh, 3 mm in diameter) that was previously covered by a thin carbon layer (support film). These samples were also analyzed using SEM operated at 15 kV and 5 kV accelerating voltage, 140 pA probe current, 2,000 cps as average count rate on the whole spectrum, and a counting time of 60 second. [0077] Electrodes were operated under HER conditions for 6 hours prior to analysis in either 1M NaOH or 1M H2SO4 under continuous H2 bubbling. Then quickly removed from the cell and rinsed in copious amounts of Nanopure water followed by light rinsing in ethanol and dried at room temperature. The solution exposed microparticles were removed by scratching the surface of the electrode lightly in a drop of high purity acetone. The acetone was then removed and dropped onto a lacey carbon film on an Au-grid. After drying the samples was examined in the HRTEM microscope. Example 6. Synthesis of MoP2 Microparticles Using Hydrothermal Method [0078] Mo-P Microparticles were also successfully prepared by a hydrothermal method. In a typical synthesis, molybdenum (V) chloride salt (7 g Mo2Cl10) and red phosphorus (12 g) were dissolved in deionized water (pH = 6-7). The sample was then transferred into a Teflon-sealed autoclave reactor and was heated to 190°C for 24 h. After completion of the reaction, the mixture was allowed to cool down to room temperature. The black solid product formed was isolated by centrifugation and unreacted species were removed by washing with water (until the supernatant is a clear solution). The isolated product was further washed with 3% HCl to remove the surface phosphate/ oxide species, followed by ethanol wash in the end. The as-synthesized materials were dried at 60 °C for 6 h and termed MoP2-HT. The as-synthesized powder was then annealed in 1% H2 for 2h at 350oC to impart crystallinity. 20 168858578.1
Docket No.070439.01870 Example 7. Synthesis of MoP2 Microparticles Using Amine Ligand-Assisted Hydrothermal Method [0079] Synthesis of Mo-P microparticles was also achieved by ligand-assisted hydrothermal method. In a typical synthesis, molybdenum (V) chloride (7 g Mo2Cl10) and red phosphorus (12 g) were dissolved in 100 mL ethylenediamine and deionized water (1:1 ratio). The sample was then transferred into a Teflon-sealed autoclave reactor and was heated to 190°C for 24 h. After completion of the reaction, the mixture was allowed to cool down to room temperature. The black solid product formed was isolated by centrifugation and unreacted species including surfactant molecules were removed by washing with water (until the supernatant is a clear solution). The isolated product was further washed with 3% HCl to remove the surface phosphate/ oxide species, followed by ethanol wash in the end. The as-synthesized materials were dried at 60 °C for 6 h and termed MoP2-EDA-HT. The as-synthesized powder was then annealed in 1%H2 for 2h at 350oC to impart crystallinity. Industrial Application [0080] Electrocatalysts for the direct CO2 reduction to hydrocarbons may be realized within electrolyzers of similar types to the chlor-alkali producing cells currently used on an industrial scale. CO2 sources could be point-sources such as power stations, cement plants, or similar large CO2 emitting industries, or from extraction directly from the atmosphere. [0081] Without further elaboration, it is believed that one skilled in the art, using the preceding description, can utilize the present disclosure to its fullest extent. Furthermore, while the present disclosure has been described with respect to aforementioned embodiments and examples, it should be appreciated that other embodiments utilizing the concept of the present disclosure are possible, and within the skill of one trained in the art, without departing from the scope of the disclosure. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the disclosure in any way whatsoever. 21 168858578.1