Catalytic electrode and photoelectrode for reduction of carbon dioxide and carbon monoxide to methanol

Abstract

An electrolytic device, photoelectrode, and method for inducing an electrochemical reduction of a feed gas, comprising an anode and a hybrid cathode, the hybrid cathode comprising a cathode, a microporous layer disposed on one side of the cathode; a cathode catalyst positioned on the surface of the microporous layer, a gas channel fluidly connected to the microporous layer, containing a quantity of a feed gas, an electrolyte channel fluidly connected to the cathode catalyst containing a quantity of electrolyte, wherein the hybrid cathode is configured to induce an electrochemical reaction in the feed gas to produce methanol, and wherein the cathode catalyst comprises a compound represented by General Formula (I).

Description

CATALYTIC ELECTRODE AND PHOTOELECTRODE FOR REDUCTION OF CARBON DIOXIDE AND CARBON MONOXIDE TO METHANOLCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 63 / 518,673, filed on August 10, 2023, incorporated herein by reference in its entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with government support under grant numbers CHE- 1651717 and CHE-2154724 awarded by the National Science Foundation and grant number DE- SC0021173 awarded by the Department of Energy. The government has certain rights in the invention.BACKGROUND OF THE INVENTION

[0003] Atmospheric CO2 is an abundant, inexpensive, and renewable feedstock for the synthesis of carbon-containing materials. Directly harnessing atmospheric or industrial CO2 as a carbon source, for example by converting CO2 emissions to clean fuels under mild conditions, would help alleviate the environmental problems associated with increasing levels of atmospheric CO2 and could provide significant economic benefits, particularly if such an approach could be powered by renewable electricity. However, existing artificial systems that utilize renewable electricity or direct solar radiation for the conversion of CO2 or CO are limited in their products and energy efficiencies, which hinders their commercial application.

[0004] The rising carbon dioxide (CO2) level in the atmosphere has become a critical concern due to its potent effects on the global climate system (Lewis, N. S. 2016, Science, 351; Chu, S. et al., 2017, Nat. Mater., 16: 16). Electrochemical reduction of CO2 to commodity chemicals and fuels provides a sustainable technical solution to mitigating CO2 emissions and closing the carbon loop (Zhang, H. et al., 2018, ACS Catal., 9:49; Franco, F. et al., 2020, Chem. Soc. Rev., 49:6884; Nguyen, T. N. et al., 2020, ACS Catal. 10: 10068; Francke, R. et al., 2018, Chem. Rev., 118:4631). Substantial progress has been made on heterogeneous metallic catalysts(e g., Cu, Ag, Au, Bi, etc.) for converting CCh into a large variety of value-added products such as carbon monoxide (CO), formic acid / formate (HCOOH / HCOO ), methane (CH4), ethanol (CH3CH2OH), and ethylene (C2H4) (Dinh, C. T. et al., 2018, Science, 360:783; Luo, M. et al., 2019, Nat. Commun. 10:5814; Xia, C. et al., 2019, Nat. Energy, 4:776; Monteiro, M. C. O. et al., 2021, Nat. Commun. 12:4943; Weng, Z. et al., 2018, Nat. Commun., 9:415; Jia, L. et al., 2021, Angew. Chem., Int. Ed. Engl., 60:21741; Guan, A. et al., 2020, ACS Energy Lett., 5, 1044). However, the presence of many different sites on metal surfaces leads to poor selectivity and surface instability during the reaction. In addition, no heterogeneous metal electrocatalysts have been reported capable of selectively reducing CO2 or CO into methanol with appreciable rate and selectivity. Methanol is a highly desirable product from CO2 or CO electrochemical reduction as it is an energy-dense liquid hydrocarbon with broad applications in sectors such as maritime shipping and petrochemicals.

[0005] Thus, there is a need in the art for an improved catalytic electrode that effectively converts CO2 to liquid fuels such as methanol to provide sustainable power for human activities with high Faradaic efficiencies and partial current densities. The present invention satisfies that need.SUMMARY OF THE INVENTION

[0006] In one aspect, the present invention relates to an electrolytic device for electrochemical reduction, comprising: an anode and a hybrid cathode, the hybrid cathode comprising: a cathode; a microporous layer; a cathode catalyst; a gas channel fluidly connected to the microporous layer; and an electrolyte channel fluidly connected to the cathode catalyst; wherein the cathode catalyst comprises a compound represented by General Formula (I):General Formula (I) wherein M is a transition metal; wherein Z1, Z2, Z3, and Z4are each independently CR’ or N; wherein R1, R2, R3, R4, and R’ each independently represent mono or di-substitution, or no substitution; wherein R1, R2, R3, R4, and R’ are each independently selected from the group consisting of hydrogen, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and wherein any two adjacent substituents are optionally joined to form a ring which may optionally be further substituted.

[0007] In one embodiment, M is cobalt. In one embodiment, Z1, Z2, Z3, and Z4are each N.

[0008] In one embodiment, the cathode catalyst comprises a compound represented by General Formula (I) which is further represented by General Formula (II):General Formula (II), wherein R1’, R2’, R3’, and R4’ are each independently selected from the group consisting of hydrogen, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryl oxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and wherein any two adjacent substituents are optionally joined to form a ring which may optionally be further substituted.

[0009] In one embodiment, wherein the compound represented by General Formula (I) is further substituted by at least one amino group. In one embodiment, the compound represented by General Formula (I) is further substituted by at least one alkoxy group.

[0010] In one embodiment, at least one of R1’, R2’, R3’, and R4’ is an amino group. In one embodiment, at least one of R1’, R2’, R3’, and R4’ is an alkoxy group.

[0011] In one embodiment, the compound represented by General Formula (I) is dispersed onto an allotrope of carbon.

[0012] In one embodiment, the microporous layer comprises a polymer and an allotrope of carbon.

[0013] In one embodiment, the cathode catalyst comprises a compound represented by General Formula (I) which is further represented by General Formula (III):General Formula (III).

[0014] In one aspect, the present invention is drawn to a method for inducing an electrochemical reaction in a feed gas, comprising: providing a microporous layer configured to be substantially permeable to a feed gas; exposing a flow of the feed gas to the microporous layer; passing a quantity of the feed gas through the microporous layer to the catalyst layer; and inducing an electrochemical reaction in the quantity of the feed gas with the electrode and the catalyst; wherein the catalyst comprises a compound represented by General Formula (I):General Formula (I) wherein M is a transition metal; wherein Z1, Z2, Z3, and Z4are each independently CR’ or N; wherein R1, R2, R3, R4, and R’ each independently represent mono or di-substitution, or no substitution; wherein R1, R2, R3, R4, and R’ are each independently selected from the group consisting of hydrogen, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and wherein any two adjacent substituents are optionally joined to form a ring which may optionally be further substituted; and wherein the catalyst may optionally further comprise an electrolyte.

[0015] In one embodiment, the feed gas comprises at least one gas selected from the group consisting of CO and CO2.

[0016] In one embodiment, the electrolyte is selected from the group consisting of calcium salts, chloride salts, magnesium salts, potassium salts, sodium salts, weak acids, weak bases, and combinations thereof.

[0017] In one embodiment, the electrochemical reaction is a 4-electron reduction of the feed gas. In one embodiment, the electrochemical reaction is a 6-electron reduction of the feed gas.

[0018] In one embodiment, the catalyst is dispersed on an allotrope of carbon. In one embodiment, the allotrope of carbon is a multi-walled carbon nanotube.

[0019] In one aspect, the present invention is drawn to thin film comprising a microporous layer and a cathode catalyst; wherein the cathode catalyst comprises a compound represented by General Formula (I):General Formula (I) wherein M is a transition metal; wherein Z1, Z2, Z3, and Z4are each independently CR’ or N; wherein R1, R2, R3, R4, and R’ each independently represent mono or di -substitution, or no substitution; wherein R1, R2, R3, R4, and R’ are each independently selected from the group consisting of hydrogen, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and wherein any two adjacent substituents are optionally joined to form a ring which may optionally be further substituted.

[0020] In one embodiment, the microporous layer is comprised of polytetrafluoroethylene (PTFE) blended with carbon black nanoparticles.BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The foregoing purposes and features, as well as other purposes and features, will become apparent with reference to the description and accompanying figures below, which are included to provide an understanding of the invention and constitute a part of the specification, in which like numerals represent like elements, and in which:

[0022] Fig. 1 depicts a set of chemical structures.

[0023] Fig. 2 depicts broadly cobalt phthalocyanine (CoPc) and derivatives.

[0024] Fig. 3, comprising Fig. 3A and Fig. 3B, depicts an electrochemical reaction device and representative measurements carried out using the device. Fig. 3 A depicts a membraneelectrode assembly (MEA) electrolyzer. Fig. 3B depicts electrochemical reduction measurements of CO2 (left) and CO (right) in the MEA electrolyzer.

[0025] Fig. 4 depicts electrocatalytic performance for CO-to-CHsOH by substituted CoPc molecules.

[0026] Fig. 5 depicts CO-to-CHsOH conversion catalyzed by CoPc-NEh / carbon nanotube (CNT) and current challenges and progress. Color code: oxygen, red; carbon, grey; hydrogen, white; nitrogen, blue; cobalt, pink.

[0027] Fig. 6, comprising Fig. 6A through Fig. 6C, depicts improving methanol selectivity by enhancing CO mass transport. Fig. 6A depicts a schematic of CO reduction to methanol catalyzed by CoPc-NFE / CNT loaded on carbon fiber paper with and without microporous layer (MPL) coating. Fig. 6B depicts a graph of product selectivity (Faradaic efficiency). Fig. 6C depicts partial current density for methanol and hydrogen versus applied electrode potential measured in 0.1 M aqueous KHCO3. Error bars represent standard deviations based on at least three independent experiments.

[0028] Fig. 7 depicts representative data for how the microporous layer enhances CO transport to active sites and increases FE from 44% to 66%.

[0029] Fig. 8 depicts CO electroreduction in varied electrolyte catalyzed by CoPc- NH2 / CNT.

[0030] Fig. 9 depicts representative current profiles of CO electroreduction catalyzed by CoPc-NFE / CNT at varied applied potential in 0.1 M aqueous KHCO3.

[0031] Fig. 10, comprising Fig. 10A through Fig. 10D, depicts kinetic analysis for methanol production from CO electroreduction catalyzed by CoPc-NFE / CNT. Fig. 10A depicts RHE scale Tafel curves for methanol formation at different electrolyte pH. Fig. 10B depicts SHE scale Tafel curves for methanol formation at different electrolyte pH. Fig. 10C depicts isotopic labeling experiments measured in KHCO3 / H2O and KDCO3 / D2O electrolytes. Fig. 10D depicts a schematic of reaction pathways leading to methanol based on the kinetic results. Error bars represent standard deviations based on at least three separate experiments.

[0032] Fig. 11, comprising Fig. 11 A through Fig. 1 ID, depicts proton donor effects on methanol production from CO electroreduction catalyzed by C0PC-NH2 / CNT. Fig. 11A depicts agraph of Faradaic efficiency and partial current density of methanol in different electrolytes. Fig. 1 IB depicts methanol partial current density versus proton donor concentration. [HA] represents either [HCO3 ] or [H2PO4 ]. The potential for all electrolyses was kept at -1.35 V vs. SHE. Fig. 11C depicts H2 partial current density versus proton donor concentration. [HA] represents either [HCCh’] or [H2PO4"]. The potential for all electrolyses was kept at -1.35 V vs. SHE. Fig. 1 ID depicts a schematic of HCCh’ as a proton donor enhancing the proton-coupled electron transfer rate-determining step (PCET RDS) for methanol production.

[0033] Fig. 12, comprising Fig. 12A through Fig. 12C, depicts dependence of CO electroreduction on HCO3- concentration. Fig. 12A depicts faradaic efficiency and partial current density of methanol produced in electrolyte with varied HCO3- concentration. Fig. 12B depicts reaction order of methanol formation with respect to HCO3- concentration. Fig. 12C depicts reaction order of H2 formation with respect to HCO3- concentration. Electrolyte was prepared by dissolving NaHCO3 and NaC104 (when needed) in water to reach desired HCO3- concentration and maintain a constant cation strength of 0.5 M.

[0034] Fig. 13, comprising Fig. 13 A through Fig. 13D, depicts the mechanism-guided realization of high methanol selectivity. Fig. 13A depicts the pco dependent methanol production rate from CO reduction catalyzed by C0PC-NH2 / CNT in 0.1 M aqueous KHCO3. Fig. 13B depicts a schematic showing that CO coverage on catalyze surface increases with CO pressure. Color code: oxygen, red; carbon, grey; hydrogen, white; nitrogen, blue; cobalt, pink. Fig. 13C depicts a schematic of two compartment high pressure electrochemical cell used in this work. WE, RE and CE represent working, reference and counter electrodes, respectively. AEM represents anion exchange membrane. Fig. 13D depicts the FE and partial current densities for methanol versus electrode potential measured under 10 atm CO in 0.1 M aqueous KHCO3.

[0035] Fig. 14 depicts faradaic efficiency and partial current density of methanol produced at varied CO pressure (total pressure 1 atm, balanced with N2) in 0.1 M KHCO3.

[0036] Fig. 15, comprising Fig. 15A through Fig. 15F, depicts CO partial pressure effect in varied electrolytes. Fig. 15A depicts faradaic efficiency and partial current density of methanol produced at varied CO pressure (total pressure 1 atm, balanced with N2) of 0.035 M K2HPO4 + 0.03 M KH2PO4 (pH=7.0). Fig. 15B depicts corresponding reaction order with respect to CO by plotting log( / M ethanol) versus log( / ?CO). Fig. 15C depicts faradaic efficiency and partial currentdensity of methanol produced at varied CO pressure of 0.05 M K2CO3 (pH=l 1 .3). Fig. 15D depicts corresponding reaction order with respect to CO by plotting log( / Methanol) versus log(pCO). Fig. 15E depicts faradaic efficiency and partial current density of methanol produced at varied CO pressure of 0.1 M KOH (pH=13.2). Fig. 15F depicts corresponding reaction order with respect to CO by plotting log( / Methanol) versus log(pCO).

[0037] Fig. 16 depicts representative data in how high pressure CO enhances faradaic efficiency for methanol to >80%.

[0038] Fig. 17, comprising Fig. 17A through Fig. 17C, depicts detection of CD3OD and CH3OH by gas chromatography (GC)-mass spectrometry (MS). Fig. 17A depicts MS signal of standard CH3OH aqueous solutions with different concentrations (0.1, 0.5, 1.0, 1.5 and 2.0 mM). Fig. 17B depicts a representative calibration curve obtained by plotting integrated peak area versus methanol concentration. Fig. 17C depicts faradaic efficiency and partial current density of deuterated methanol produced at varied electrode potential in 0.1 M KDCO3 in D2O.

[0039] Fig. 18 depicts optical profiler three-dimensional image of Si micropillar array (SMA) with 17.8 pm pillars depth.

[0040] Fig. 19, comprising Fig. 19A through Fig. 19E, depicts typical fabrication method of SMA and CFXcoating. Fig. 19A depicts a schematic of the fabrication method. Fig. 19B depicts a scanning electron microscopy (SEM) image of SMA. Fig. 19C depicts a SEM image of SMA coated with CNT / C0PC-NH2 catalyst. Fig. 19D depicts a SEM image of the top view of a single Si pillar coated with CNT / C0PC-NH2. Fig. 19E depicts a SEM image of the side view of a single Si pillar coated with CNT / C0PC-NH2.

[0041] Fig. 20, comprising Fig. 20A through Fig. 20E, depicts conversion performance. Fig. 20A depicts a schematic illustration of the petroelectrochemical (PEC) cell device. Fig. 20B depicts CO2 reduction current density and faradaic efficiency of SMA-CNT / C0PC-NH2 under illumination and -0.7 V applied voltage. Methanol concentration is measured after the 30 mins reaction as an average. Fig. 20C depicts stability test of SMA-CNT / C0PC-NH2 under illumination and constant photocurrent of 15 mA cm’2. Fig. 20D depicts performance comparison of normal SMA-CNT / C0PC-NH2, graphene oxide (GO) / CoPc on planar Si, and carbon fiber paper (CFP)-CNT / CoPc-NH2 (electrocatalysis on CFP without light). Fig. 20E depicts in-situ Raman studies with -0.9 V applied potential showing the generated methanol and CO.

[0042] Fig. 21 , comprising Fig. 21 A through Fig. 21E, depicts characterization data of SMA. Fig. 21A depicts a comparison of methanol selectivity and partial current of normal SMA- CNT / CoPc-NFb (noted as 18-CFX), SMA-CNT / CoPc-NH without CFXcoating (noted as 18), and planar Si-TiCh-GO / CoPc (noted as Planar). Fig. 21B depicts x-ray photoelectron spectroscopy (XPS) of SMA-CNT / CoPc-NFb before (up) and after 4 hours PEC (bottom). Fig. 21C depicts a SEM image of the side wall of a single Si pillar (left), and the TEM image and energy-dispersive spectroscopy (EDS) of the boxed area cut using focused ion beam (FIB). Fig.2 ID depicts a schematic illustration of the structure of Si pillars. Fig. 2 ID depicts contact angle measurements on SMA (up), and SMA without CFXcoating (bottom).

[0043] Fig. 22 depicts the photoelectrocatalytic performance of SMA-CNT / CoPc-NFE without CFx coating. The top-left corner indicates the pillars depth and pitch (D-P). Electrodes were cleaned with HF before drop casting catalyst to remove the insulating native oxide.

[0044] Fig. 23 depicts a SEM image of the FIB-cut Si sidewall cross-section.DETAILED DESCRIPTION

[0045] It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for the purpose of clarity, many other elements found in related systems and methods. Those of ordinary skill in the art may recognize that other elements and / or steps are desirable and / or required in implementing the present invention. However, because such elements and steps are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements and steps is not provided herein. The disclosure herein is directed to all such variations and modifications to such elements and methods known to those skilled in the art.

[0046] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, exemplary methods and materials are described.

[0047] As used herein, each of the following terms has the meaning associated with it in this section.

[0048] The articles “a” and “an” are used herein to refer to one or to more than one (z.e., to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element.

[0049] “About” as used herein when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of ±20%, ±10%, ±5%, ±1%, and ±0.1% from the specified value, as such variations are appropriate.

[0050] Throughout this disclosure, various aspects of the invention can be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 2.7, 3, 4, 5, 5.3, 6 and any whole and partial increments therebetween. This applies regardless of the breadth of the range.

[0051] Certain exemplary embodiments of the present invention disclosed herein may recite a microporous layer, configured to increase localized concentrations of a target gas around a catalyst or device configured to induce a chemical reaction with the target gas. Although some examples may specifically relate to carbon dioxide, it is understood that certain systems and methods of the present invention may be used with any other gas as a target gas. Exemplary target gases include, but are not limited to, CO2 and CO.

[0052] Molecular catalysts are promising alternatives to heterogeneous metallic catalysts because their well-defined structures provide a precise model for theoretical calculations and experimental studies to understand the reaction mechanism and thereby improve the catalytic performance (Wang, J. et al., 2021, Sci. Adv., 7:eabf3989; Wu, Y. et al., 2021, Acc. Chem. Res., 54:3149; Cao, R., 2022, ChemSusChem, 15:e202201788; Chang, Q. et al., 2022, J. Am. Chem. Soc., 144:16131; Soucy, T. L. et al., 2022, Acc. Chem. Res., 55:252). Many molecular catalystswith various transition metal centers such as Co, Ni, Fe and Mn have been reported to show appreciable activity in CO2 electroreduction (Zhang, X. et al., 2017, Nat. Commun., 8:14675; Zhang, X. et al., 2020, Nat. Energy, 5:684; Guo, H. et al., 2022, Chin. J. Catal., 43:3089; Ronne, M. H. et al., 2020, J. Am. Chem. Soc., 142:4265; Zhang, Z. et al., 2018, Angew. Chem., Int. Ed. Engl., 57:16339; Soucy, T. L. et al., 2021, ACS Appl. Energy Mater., 5: 159). Most of them generate 2-electron reduction products such as CO and formate. Further reduced products, although desirable, are hard to obtain.

[0053] In one aspect, the present invention relates to a structured electrode for improving the efficiency of an electrochemical reduction of CO2 or CO to yield methanol. In some embodiments, an electrode of the present invention comprises a gas diffusion electrode (GDE), a microporous layer, and a catalyst.

[0054] The microporous layer may comprise an arrangement of one or more materials with a total overall thickness in a range of 1 pm to 1 mm, or in some embodiments about 40 pm. In some embodiments, the microporous layer has pores with diameter in a range of 0.05 pm to 1 pm.

[0055] The gas diffusion electrode (GDE) may comprise for example of a carbon fiber paper and may have a thickness in a range of 100 pm to 1 mm, or 300 pm to 500 pm. In one embodiment, the GDE may have a thickness of about 370 pm. In some embodiments, the GDE may itself be porous, for example to allow for the feed gas to pass through to the microporous layer and then to the catalyst. The GDE may have pores having a diameter of around 10 pm.

[0056] One exemplary catalyst suitable for use with an embodiment of the present invention is cobalt phthalocyanine (CoPc) molecules anchored on carbon nanotubes (CoPc / CNT). In one embodiment, the catalyst converts pure CO2 to CO and methanol. In one embodiment, the catalyst in an electrolytic cell converts pure CO2 to CO and methanol.

[0057] In some embodiments, substituents on the Pc ligand may be adjusted, such as to tune the steric or electronic properties of the resultant complex. In one embodiment, the Pc ligand may include electron-donating substituents. Non-limiting examples of electron donating substituents include amino groups, hydroxyl groups, alkoxy groups, alkyl thiols, alkyl groups, and alkylamino groups.

[0058] The term "alkyl" by itself or as part of another substituent, refers to a straight or branched saturated hydrocarbon group joined by single carbon-carbon bonds having 1 to 10 carbon atoms, for example 1 to 8 carbon atoms, for example 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms. When a subscript is used herein following a carbon atom, the subscript refers to the number of carbon atoms that the named group may contain. Thus, for example, Ci-4 alkyl means an alkyl group of one to four carbon atoms. Examples of alkyl groups are methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, 2-methylbutyl, pentyl (e.g. pentyl isoamyl) and its isomers, hexyl and its isomers, heptyl and its isomers and octyl and its isomers.

[0059] In one embodiment, the Pc ligand may include electron-withdrawing substituents. As used herein, the term "electron-withdrawing" as applied to a substituent or group refers to the ability of a substituent or group to draw electrons to itself more so than a hydrogen atom would if it occupied the same position in the molecule. This term is well understood by one skilled in the art and is discussed in Advanced Organic Chemistry, by J. March, 4thEd. John Wiley and Sons, New York, N.Y. pp. 18-19 (1992), and the discussion therein is incorporated by reference. Nonlimiting examples of electron withdrawing substituents include halo, especially fluoro, chloro, bromo, iodo; nitro (NO2); cyano (CN); trifluoromethyl (CF3); trichloromethyl; carboxy; formyl; lower alkanoyl; carboxyamido; aryl; and aryl lower alkanoyl.

[0060] In some embodiments, the catalyst is represented by General Formula (I):General Formula (I) wherein M is a transition metal; wherein Z1, Z2, Z3, and Z4are each independently CR’ or N; wherein R1, R2, R3, R4, and R’ each independently represent mono or di -substitution, or no substitution;wherein R1, R2, R3, R4, and R’ are each independently selected from the group consisting of hydrogen, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and wherein any two adjacent substituents are optionally joined to form a ring which may optionally be further substituted.

[0061] In some embodiments, the catalyst is selected from the group consisting of CoPc, CoPc-CN, C0PC-NH2, COPC-NO2, FePc, FePc-CN, FePC-NH2, FePC-NCh, NiPc, NiPc-CN, N1PC-NH2, NiPC-NCh, CuPc, CuPc-CN, CuPC-NH2, and CuPC-NCh.

[0062] The present disclosure further includes various methods for inducing an electrochemical reaction in a feed gas. One exemplary method includes passing a quantity of the feed gas to an electrode, exposing the constituent gases to a microporous layer that enhances mass transport of some components of the feed gas to the catalyst positioned on the microporous layer, and inducing an electrochemical reaction in the first constituent gas with the electrode and the catalyst.

[0063] In some embodiments, the end products of a system or method of the present invention comprise carbon monoxide (CO). In some embodiments, CO may be further electrochemically reduced to methanol, or used as a feedstock in a further process, for example the Fischer-Tropsch process to produce liquid fuels as a final product.

[0064] In one embodiment, an electrolytic device 400 for electrochemical reduction comprises an anode 403 and a hybrid cathode 402. In some embodiments, the hybrid cathode 402 comprises a cathode, a microporous layer, a cathode catalyst, a gas channel fluidly connected to the microporous layer, and an electrolyte channel fluidly connected to the cathode catalyst. In some embodiments, the device further includes a separating membrane 405, which may be for example an anion exchange membrane (AEM), between the anode 403 and cathode 402.

[0065] In some embodiments, the device 400 is housed within a membrane-electrode assembly (MEA) electrolyzer 499. In some embodiments, the electrolyzer 499 comprises asandwich construction including support plates 410, gas channeling plates 409 positioned between the support plates 410, and device 400 between the gas channeling plates 409.

[0066] In some embodiments, the support plates 410 include one or more inlet ports (406, 407) which may be configured to supply an anolyte and / or a feed gas to the device 400. In some embodiments, the support plates 410 may include one or more outlet ports 408 which may be configured to output a product of the reaction of the device 400. In some embodiments, the one or more inlet ports (406, 407) and / or outlet ports 408 are fluidly connected to the device 400 via the gas channeling plates 409.

[0067] In some embodiments, one or more of the gas channeling plates 409 may include a gas channel 404 configured to direct gas across the anode 403 and / or cathode 402 of device 400. In some embodiments, the gas channel 404 is fluidly connected to the inlet ports (406, 407) and / or outlet ports 408.

[0068] In some embodiments, the voltage source 401 is connected across the anode 403 and cathode 402 via the gas channeling plates 409 and / or the support plates 410. In some embodiments, the anode 403 and cathode 402 are each electrically connected to separate gas channeling plates 402 and / or support plates 410. In some embodiments, the separating membrane 405 is electrically insulating.

[0069] In some embodiments, the support plates 410 have a length in the range of 5 cm to 15cm, a width in the range of 5 cm to 15 cm, and / or a thickness in the range of 0.1 cm to 3 cm. In some embodiments the support plates 410 comprise aluminum, steel, stainless steel, titanium, and / or any other suitable material. In some embodiments, the support plates 410 have a length of10 cm, a width of 10 cm, and a thickness of 1 cm and are made of aluminum. In some embodiments, the inlet and outlet ports have fittings of type 1 / 8 inch NPT or similar. In some embodiments, the gas channeling plates 409 have a length of 1 cm to 11 cm, a width of 1 cm to11 cm, and / or a thickness of 0.1cm to 3 cm. In some embodiments, the gas channeling plates 409 have a length of 6 cm, a width of 6 cm, and a thickness of 1 cm. In some embodiments, the gas channeling plates 409 are made of stainless steel, aluminum, steel, titanium, and / or other suitable material. In some embodiments, serpentine gas channel flow field has a depth in the range of 0.1 mm to 10 mm, a length in the range of 1 cm to 3 cm, a width in the range of 1 cm to 3 cm, and thereby cover an area of approximately in the range of 1 cm2to 9 cm2. In someembodiments the serpentine gas channel flow field has a depth of 1 mm, length of 2.25 cm and width of 2.25 cm, thereby covering a geometric area of approximately 5 cm2.

[0070] In some embodiment, the anode 403 has a length in the range of 1 cm to 5 cm, and / or a width in the range of 1 cm to 5 cm. In some embodiments, the anode 403 has a length of 2.5 cm and a width of 2.5 cm. In some embodiments, the anode 403 comprises a titanium mesh porous transport layer coated with an oxygen evolution catalyst, for example IrOx nanoparticles supported on carbon black. In some embodiments, the separating membrane 405 comprises an ion conductive membrane, which can be either an anion exchange membrane or a proton exchange membrane with thickness between 5-200 micrometers, in some instances with a thickness of 30 micrometers, in other instances with a thickness of 70 micrometers. The cathode in some instances has a geometric area of 5 cm2.

[0071] In some embodiments the cathode catalyst comprises a compound represented by General Formula (I):General Formula (I) where M is a transition metal, where Z1, Z2, Z3, and Z4are each independently CR’ or N, where R1, R2, R3, R4, and R’ each independently represent mono or di-substitution, or no substitution; where R1, R2, R3, R4, and R’ are each independently selected from the group consisting of hydrogen, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof, and where any two adjacent substituents are optionally joined to form a ring which may optionally be further substituted.

[0072] In one aspect, an electrolytic device for electrochemical reduction of a feed gas comprises an anode and a hybrid cathode, the hybrid cathode comprising a cathode, a microporous layer disposed on one side of the cathode, and a cathode catalyst positioned on the opposite side of the cathode from the microporous layer, a power source electrically connected to the anode and the cathode and configured to induce a potential difference between the anode and the cathode, a gas channel fluidly connected to the microporous layer, containing a quantity of a feed gas, and an electrolyte channel fluidly connected to the cathode catalyst containing a quantity of electrolyte, wherein the hybrid cathode is configured to induce an electrochemical reaction in the feed gas.

[0073] In one embodiment, the device further comprises an anode catalyst positioned on the anode, and a second electrolyte channel fluidly connected to the anode catalyst. In one embodiment, the electrolyte channel and the second electrolyte channel are fluidly isolated by an anion exchange membrane. In one embodiment, the feed gas comprises CO2 and O2. In one embodiment, the feed gas includes a volumetric concentration of at least 5% O2. In one embodiment, the microporous layer comprises a polymer. In one embodiment, the catalyst comprises CoPc. In one embodiment, the electrolyte comprises KHCO3.

[0074] In one embodiment, the potential difference is about 1.0 V to about 10.0 V. In one embodiment, the potential difference is about 1.0 V to about 9.0 V. In one embodiment, the potential difference is about 1 .0 V to about 8.0 V. In one embodiment, the potential difference is about 1.0 V to about 7.0 V. In one embodiment, the potential difference is about 1.0 V to about 6.0 V. In one embodiment, the potential difference is about 1.0 V to about 5.0 V. In one embodiment, the potential difference is about 1.0 V to about 4.0 V. In one embodiment, the potential difference is about 1.0 V to about 3.0 V. In one embodiment, the potential difference is about 2.0 V to about 9.0 V. In one embodiment, the potential difference is about 2.0 V to about 8.0 V. In one embodiment, the potential difference is about 2.0 V to about 7.0 V. In one embodiment, the potential difference is about 2.0 V to about 6.0 V. In one embodiment, the potential difference is about 2.0 V to about 5.0 V. In one embodiment, the potential difference is about 2.0 V to about 4.0 V. In one embodiment, the potential difference is about 2.0 V to about 3.0 V. In one embodiment, the potential difference is about 3.0 V to about 4.0 V. In one embodiment, the potential difference is about 3.1 V.

[0075] In another aspect, a hybrid cathode for electrochemical reduction of a feed gas comprises a gas diffusion cathode comprising a plurality of pores, a microporous layer fluidly connected to a feed gas comprising a plurality of pores disposed on a side of the cathode, configured to allow at least one first molecular component of the feed gas to pass through to the cathode while substantially isolating at least one second molecular component of the feed gas from the cathode, and a cathode catalyst positioned on the opposite side of the cathode from the microporous layer, configured to catalyze electrochemical reactions of the first molecular component of the feed gas.

[0076] In one embodiment, the gas diffusion cathode comprises carbon fiber paper. In one embodiment, the microporous layer comprises a polymer. In one embodiment, the cathode catalyst comprises CoPc and carbon nanotubes. In one embodiment, the cathode catalyst comprises CoPc-CN.

[0077] In one embodiment, the microporous layer pores have a diameter of about 0.1 nm to about 1.0 nm. In one embodiment, the microporous layer pores have a diameter of about 0.1 nm to about 0.9 nm. In one embodiment, the microporous layer pores have a diameter of about 0.1 nm to about 0.8 nm. In one embodiment, the microporous layer pores have a diameter of about 0.1 nm to about 0.7 nm. In one embodiment, the microporous layer pores have a diameter of about 0.1 nm to about 0.6 nm. In one embodiment, the microporous layer pores have a diameter of about 0.1 nm to about 0.5 nm. In one embodiment, the microporous layer pores have a diameter of about 0.43 nm.

[0078] In another aspect, a method for inducing an electrochemical reaction in a feed gas comprises providing a microporous layer configured to be substantially permeable to CO2, exposing a flow of the feed gas to the microporous layer, passing a quantity of CO2 through the microporous layer to an electrode, exposing the quantity of CO2 to a catalyst positioned on the opposite side of the electrode from the microporous layer, and inducing an electrochemical reaction in the quantity of CO2 with the electrode and the catalyst.

[0079] In one embodiment, the microporous layer comprises a polymer. In one embodiment, the microporous layer pores have a diameter in a range of around 0.43 nm. In one embodiment, the method further comprises the step of using a product of the electrochemicalreaction as a feedstock in a further process. In one embodiment, the process is the Fischer- Tropsch process to produce liquid fuels.

[0080] In one aspect, the present disclosure is drawn to improvements to the cobalt phthalocyanine anchored on multi walled carbon nanotubes (CoPc / CNT) electrocatalyst, which is the only known electrocatalyst active for CO2 / CO reduction to MeOH with selectivity at or less than 40% Faradaic efficiency (FE) and partial current density at or less than 10 mA / cm2.

[0081] In one embodiment, the system is capable of reducing CO to MeOH with high selectivity (>50% FE) and activity (>20 mA / cm2). In one embodiment, this is achieved by the novel catalyst molecular structure and implementation of a microporous support. In one embodiment, the improved electrocatalyst allows for more energy efficient electrochemical CO2 / CO conversion to MeOH compared to existing state-of-the-art. In one embodiment, the improved electrocatalyst promotes higher Faradaic yield of MeOH. In one embodiment, the improved electrocatalyst promotes larger operating current density of the electrolyzer. In one embodiment, the improved electrocatalyst promotes lower overpotential for the reaction.

[0082] In one embodiment, the present invention helps create a circular carbon economy that valorizes waste CO2 streams from industrial processes. In one embodiment, the present invention allows for green MeOH production from a concentrated CO2 stream, such as those created by direct-air CO2 capture or point source emissions such as flue gas. In one embodiment, the present invention can be coupled with existing methanol-to-jet technology for production of sustainable aviation fuel.

[0083] In one aspect, the present invention is drawn to an electrolytic device for electrochemical reduction of a feed gas, comprising an anode and a hybrid cathode, the hybrid cathode comprising: a cathode; a microporous layer; a cathode catalyst; a gas channel fluidly connected to the microporous layer; and an electrolyte channel fluidly connected to the cathode catalyst; wherein the cathode catalyst comprises a compound represented by General Formula (I):General Formula (I)

[0084] In one embodiment, M is a transition metal. Exemplary metals include, but are not limited to scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, halfnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, oxides thereof, and any oxidation state thereof. In one embodiment, M is cobalt. In one embodiment, M is copper. In one embodiment, M is zinc.

[0085] In one embodiment, Z1, Z2, Z3, and Z4are each independently CR’ or N. In one embodiment, Z1, Z2, Z3, and Z4are each N. In one embodiment, Z1, Z2, Z3, and Z4are each CR’.

[0086] In one embodiment, R1, R2, R3, R4, and R’ each independently represent mono or di -substitution, or no substitution. In one embodiment, R1, R2, R3, R4, and R’ are each independently selected from the group consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, and cycloalkenyl, wherein any two adjacent substituents are optionally joined to form a ring which may optionally be further substituted.

[0087] In one embodiment, the cathode catalyst comprises a compound represented by General Formula (I) which is further represented by General Formula (II):General Formula (II), wherein R1’, R2’, R3’, and R4’ are each independently selected from the group consisting of hydrogen, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryl oxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and wherein any two adjacent substituents are optionally joined to form a ring which may optionally be further substituted.

[0088] In one embodiment, the feed gas comprises at least one gas selected from the group consisting of CO and CO2.

[0089] In one embodiment, the compound represented by General Formula (I) is further substituted by at least one amino group. In one embodiment, the compound represented by General Formula (I) is further substituted by at least one alkoxy group. In one embodiment, the compound represented by General Formula (II) is further substituted by at least one amino group. In one embodiment, the compound represented by General Formula (II) is further substituted by at least one alkoxy group.

[0090] In one embodiment, the compound represented by General Formula (I) is dispersed onto carbon nanotubes. In one embodiment, the microporous layer further comprises a carbon and fluorinated polymer mixture.

[0091] In one embodiment, the cathode catalyst comprises a compound represented by General Formula (I) which is further represented by General Formula (III):General Formula (III).

[0092] In one aspect, the present invention is drawn to A method for inducing an electrochemical reaction in a feed gas, comprising: providing a microporous layer configured to be substantially permeable to a feed gas; exposing a flow of the feed gas to the microporous layer; passing a quantity of the feed gas through the microporous layer; exposing the quantity of the feed gas to the catalyst layer positioned on the microporous layer; and inducing an electrochemical reaction in the quantity of the feed gas with the electrode and the catalyst; wherein the catalyst comprises a compound represented by General Formula (I):General Formula (I).

[0093] In one embodiment, M is a transition metal. Exemplary metals include, but are not limited to manganese, iron, cobalt, nickel, copper, zinc, oxides thereof, and any oxidation state thereof. In one embodiment, M is cobalt.[0094J In one embodiment, Z1, Z2, Z3, and Z4are each independently CR’ or N. In one embodiment, Z1, Z2, Z3, and Z4are each N. In one embodiment, Z1, Z2, Z3, and Z4are each CR’.

[0095] In one embodiment, R1, R2, R3, R4, and R’ each independently represent mono or di -substitution, or no substitution. In one embodiment, R1, R2, R3, R4, and R’ are each independently selected from the group consisting of hydrogen, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, and cycloalkenyl, wherein any two adjacent substituents are optionally joined to form a ring which may optionally be further substituted.

[0096] In one embodiment, the catalyst further comprises an electrolyte. Exemplary electrolytes include, but are not limited to, calcium salts, chloride salts, magnesium salts, potassium salts, sodium salts, weak acids, weak bases, and combinations thereof. In one embodiment, the electrolyte is a salt. In one embodiment, the electrolyte is a potassium salt. In one embodiment, the electrolyte is KHCO3.

[0097] In one embodiment, the feed gas comprises at least one gas selected from the group consisting of CO and CO2.

[0098] In one embodiment, the electrochemical reaction is a 4-electron reduction of the feed gas. In one embodiment, the electrochemical reaction is a 6-electron reduction of the feed gas.

[0099] In one embodiment the catalyst is dispersed on an allotrope of carbon. Exemplary allotropes of carbon include, but are not limited to, graphite, fullerenes, fullerites, amorphous carbon, carbon nanotubes, cyclocarbons, and nanobuds. In one embodiment, the allotrope of carbon is a multi-walled carbon nanotube.

[0100] In one embodiment, the present invention is drawn to a method of making methanol in an electrolytic device for electrochemical reduction of a feed stream comprising either CO2 or CO: providing an electrolytic device of claim 1; providing a microporous layer configured to be substantially permeable to a feed gas; exposing a flow of the feed gas to the microporous layer; and passing a quantity of the feed gas through the microporous layer to the electrolytic device for electrochemical reduction of the feed gas to produce methanol.

[0101] In one aspect, the present invention is drawn to thin film comprising a microporous layer and a cathode catalyst; wherein the cathode catalyst comprises a compound represented by General Formula (I):General Formula (I) wherein M is a transition metal; wherein Z1, Z2, Z3, and Z4are each independently CR’ or N; wherein R1, R2, R3, R4, and R’ each independently represent mono or di -substitution, or no substitution; wherein R1, R2, R3, R4, and R’ are each independently selected from the group consisting of hydrogen, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and wherein any two adjacent substituents are optionally joined to form a ring which may optionally be further substituted.A method of making methanol in an electrolytic device for electrochemical reduction of a feed stream comprising either CO2 or CO: providing an electrolytic device of claim 1 ; providing a microporous layer configured to be substantially permeable to a feed gas; exposing a flow of the feed gas to the microporous layer; and passing a quantity of the feed gas through the microporous layer to the electrolytic device for electrochemical reduction of the feed gas to produce methanol.

[0102] The present invention is drawn to a photoelectrode for electrochemical reduction, comprising: a silicon substrate coated with at least one polymer; and a compound represented by General Formula (I):General Formula (I) wherein M is a transition metal; wherein Z1, Z2, Z3, and Z4are each independently CR’ or N; wherein R1, R2, R3, R4, and R’ each independently represent mono or di -substitution, or no substitution; wherein R1, R2, R3, R4, and R’ are each independently selected from the group consisting of hydrogen, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein any two adjacent substituents are optionally joined to form a ring which may optionally be further substituted; and wherein the compound is optionally deposited on a carbon allotrope.

[0103] In one embodiment, the silicon substrate is a micropillar array.EXPERIMENTAL EXAMPLES

[0104] The invention is further described in detail by reference to the following experimental examples. These examples are provided for purposes of illustration only, and are not intended to be limiting unless otherwise specified. Thus, the invention should in no way be construed as being limited to the following examples, but rather, should be construed to encompass any and all variations which become evident as a result of the teaching provided herein.

[0105] Without further description, it is believed that one of ordinary skill in the art can, using the preceding description and the following illustrative examples, make and utilize the system and method of the present invention. The following working examples therefore, specifically point out the exemplary embodiments of the present invention, and are not to be construed as limiting in any way the remainder of the disclosure.Example 1 : C0PC-NH2 / CNT catalyzes electrochemical reduction of CO to methanol

[0106] A significant advantage of the disclosed molecular CoPc-based catalyst materials is that their catalytic sites can be tailored by chemical synthesis to introduce substituents that might further enhance performance. Prior work has revealed that electron-withdrawing substituents on CoPc can improve the electrocatalytic activity for CO2 reduction to CO. (Zhang X, Wu Z, Zhang X, et al. Highly selective and active CO2 reduction electrocatalysts based on cobalt phthalocyanine / carbon nanotube hybrid structures. Nature Communications 2017; 8: 14675, incorporated herein by reference). Prior work has also revealed that amino-substituted CoPc molecules have far superior stability for electrochemical CO2 reduction to methanol as shown in Fig. 1 (Wu, Y., Jiang, Z., Lu, X. et al. Domino electroreduction of CO2 to methanol on a molecular catalyst. Nature 2019; 575, 639-642, incorporated herein by reference). Hence, in some embodiments, a catalyst of the present invention includes prepared cyano-, nitro- and amino-substituted CoPc molecules, for example as shown in Fig. 2, and their corresponding hybrids with CNTs. Fig. 2 depicts exemplary molecular structures of (a) CoPc, (b) CoPc-CN, (c) CoPc-NO2 and (d) C0PC-NH2.

[0107] In some embodiments, a hybrid electrode comprising one or more of the enhancements disclosed herein may be integrated into a membrane-electrode assembly (MEA) electrolyzer 499. One such exemplary embodiment is shown in Fig. 3A. As seen in Fig. 3A, a voltage source 401 is connected between cathode 402 and anode 403, configured to induce a potential difference between the anode and the cathode, which may both in some embodiments be GDEs. Electrolytes are introduced via a flow channel to the anode, including in some embodiments an anolyte in contact with an anode catalyst. The anode and cathode may be separated from one another by a separating membrane 405, which may be for example an anion exchange membrane (AEM).

[0108] Measurements shown in Fig. 3B were carried out in a 1 m2MEA electrolyzer with components as depicted in Fig. 3A. To prepare the cathode catalyst, 4 g of C0PC-NH2 / CNT catalyst powder was first dispersed in 4 L of ethanol with 30 pL of 5 wt% Nafion solution and subjected to ultrasonication. This catalyst ink was then sprayed onto a 2.5 .5 m2 carbon fiber paper (Sigracet 29BC, Fuel Cell Store) to reach a catalyst area loading of 1 g / cm2. The anode of IrOx / Ti mesh (iridium oxide supported on titanium mesh) was purchased (Fuel Cell Store). An anion-exchange membrane (Sustainion X37-50 Grade 60, Dioxide Materials) was used. 0.1 M KHCO3 electrolyte was used as the anolyte and was circulated using a peristaltic pump at 20 L / min. The flow rate of the CO2 or CO gas flowing into the cathode flow field was kept at 10 mL / min and 20 mL / min, respectively, by a mass flow controller (Alicat Scientific) and was first humidified before flowing into the cathode chamber. Chronopotentiometry measurements were conducted using a Biologic VMP3 potentiostat at the current ranging from 50 to 300 A / cm2. The voltage was recorded without iR correction.

[0109] The present disclosure is also drawn to improvements on the prior reaction which is still hampered by low selectivity (methanol Faradaic efficiency <40%) and poorly understood kinetics / mechanism. These limitations were addressed using a mechanism-guided reaction design approach based on systematic kinetic studies. pH-dependent Tafel analysis and kinetic isotopic effect experiments elucidated that methanol production from CO electroreduction was pH independent and was limited by the *CO hydrogenation to *CHO step in which water was the major proton source. Proton donor comparison showed that bicarbonate could promote the reaction at its optimal concentration of 0.1 M. A CO reaction order study confirmed a Henry type isotherm for CO adsorption on the catalyst surface. These mechanistic findings resulted in an experiment which found that CO reduction in a 0.1 M bicarbonate electrolyte, under 10 atm CO pressure, and with a microporous layer on the electrode enhanced reactant transport. The reaction achieved a remarkably high methanol Faradaic efficiency of 84% with a partial current density of more than 20 mA cm'2at -0.98 V vs the reversible hydrogen electrode, making the electrochemical CO-to-methanol conversion a selective process viable for practical application.

[0110] These improvements doubled the catalyst’s selectivity for CO-to-methanol, achieving up to 70% FE under the same reaction conditions and up to 84% FE under high pressure conditions. This was achieved by modifying the molecular structure of the cobalt phthalocyanine catalyst by appending substituents to the peripheral benzene rings of themolecule. Specifically, the / ? -tetramethoxy-cobalt phthalocyanine (CoPc-4OMe) catalyst shows -20% higher methanol production rate compared to our previously disclosed molecular structure? -tetraamino-cobalt phthalocyanine (CoPc-4NH2) under the same conditions (Fig. 4). In addition, a microporous catalyst support was implemented and enhanced mass transport of CO to the catalytic active sites. Finally, high-pressure reaction conditions were used to achieve optimal catalytic performance.

[0111] The first molecular electrocatalyst consisted of amine-substituted cobalt phthalocyanine molecules supported on carbon nanotubes (CoPc-NFF / CNT), that can stably reduce CO2 to methanol (CH3OH) in significant yield (Wu, Y. et al., 2019, Nature, 575:639). The catalytic activity was hypothesized to be intrinsic to the C0PC-NH2 molecule and greatly enhanced by its electronic coupling with the highly conductive CNT support (Wu, Y. et al., 2021, Acc. Chem. Res., 54:3149). Following this initial work, more efforts were devoted to understanding and developing the reaction of CO2 or CO reduction to methanol catalyzed by CoPc-based materials (Boutin, E. et al., 2022, Chem. Eur. J., 28:e202200697; Shi, L. et al., 2022, Inorg. Chem., 61 : 16549; Boutin, E. et al., 2019, Angew. Chem., Int. Ed. Engl., 58: 16172; Chen, X. et al., 2021, Organometallics, 40:3087; Wu, Y. et al., 2020, ChemSusChem, 13:6296; Shang, B. et al., 2023, Angew. Chem., Int. Ed. Engl., 62:e202215213). However, the reaction kinetics and mechanism were not understood except that CO and formaldehyde are reaction intermediates and that CO reduction was likely rate-limiting, which hampered further improvement of the catalytic performance, as shown in Fig. 5. Thus far, the highest methanol selectivity (Faradaic efficiency, FE) achieved in CO2 / CO reduction had been approximately 40% due to the sluggish CO reduction and competition from the hydrogen evolution reaction (HER), which is well below the standard of practical application.

[0112] Systematic kinetic studies of CO electroreduction catalyzed by C0PC-NH2 / CNT were performed and successfully leveraged the derived mechanistic understanding to considerably improve the FE of methanol production by a factor of two to >80%. In response to the reactant’s low solubility in aqueous electrolyte, a microporous layer (MPL) was first introduced into the catalytic electrode structure, which enhanced the mass transport of CO and increased the methanol FE from the state-of-the-art 40% to 66%. Tafel analysis revealed an unvarying slope close to 118 mV dec'1for methanol production at electrolyte pH from 7 to 13, indicating that transfer of the first electron to CO was the rate determining step (RDS). pHdependence and isotopic labeling experiments suggested that H2O was involved as the major proton source in the RDS, although the presence of bicarbonate (HCO3 ) could further enhance proton transfer. A pressure dependence study showed that the methanol generation reaction was first order with respect to CO partial pressure, indicating a Henry type isotherm for CO adsorption on the catalyst surface. These mechanistic findings inspired experiments for CO reduction under high pressure conditions in KHCO3 electrolyte which achieved a remarkably high methanol FE of 84% with a partial current density of more than 20 mA cm'2at -0.98 V vs the reversible hydrogen electrode (RHE).

[0113] Prior work has shown that CO is always present in the products of CO2 reduction to methanol, and that CO requires almost the same electrode potential as CO2 to be reduced to methanol. This suggests that CO reduction to methanol is a harder reaction than CO2 reduction to CO, which agrees with the observation that most metal-N4 molecular electrocatalysts can only convert CO2 to CO (Zhang, X. et al., 2020, Nat. Energy, 5:684; Guo, H. et al., 2022, Chin. J. Catal. 43:3089; Zhang, Z. et al., 2018, Angew. Chem., Int. Ed. Engl., 57: 16339; Zeng, J. S. et al., 2020, Angew. Chem., Int. Ed. Engl., 59:4464). The present invention isolated the CO electroreduction reaction for investigation. It was noted that CO did not react with any commonly used electrolyte, and thus could facilitate reliable electrokinetic measurements in a wide pH range. Considering that the reactant was poorly soluble in aqueous electrolyte, the mass transport of CO was enhanced by introducing a MPL consisting of carbon particles and fluoropolymers into the electrode structure as seen in Fig. 6A. Not only did this microenvironment tune-up increase the diffusion limited current for CO reduction to enable reliable kinetic measurements, but it could also steer some C0PC-NH2 sites from catalyzing HERs to catalyzing CO reduction.

[0114] Measured at ambient temperature and pressure (pressure is 1 atm in all experiments unless specifically stated otherwise) in a 0.1 M CO-saturated KHCO3 aqueous solution, the C0PC-NH2 / CNT catalyst manifested clear potential dependence in the range of -0.62 V to -0.87 V, as seen in Fig. 6B. Methanol and H2 were the only two products detected, which implied a single reaction pathway from CO to methanol, a notable characteristic of molecular catalysts. As the applied potential decreased from -0.62 V to -0.80 V, the methanol FE increased significantly from 12% to 66%, as seen in Fig. 7, whereas the H2 FE decreased from 86% to 37%. As the potential became even more negative, the methanol FE graduallydecreased as a result of the more competitive HER. This result showed more than 50% improvement of methanol selectivity over the highest reported value which was obtained using the same catalyst supported on carbon fiber paper without MPL coating (Wu, Y. et al., 2019, Nature, 575:639). Over the potential range probed, both methanol and H2 partial current densities increased nearly exponentially from several mA cm'2to more than 10 mA cm'2, as seen in Fig. 6C, indicating no apparent CO mass transport limitation. This important improvement in reaction rate and selectivity, enabled by the improved microenvironment and interfaces near the catalyst, laid the foundation for further mechanistic / kinetic investigations of CO reduction to methanol catalyzed by C0PC-NH2 / CNT.Kinetic Studies

[0115] To probe the kinetics of methanol production, the reaction was systematically evaluated in the electrolyte pH range of 7.0-13.2 at electrode potentials between -0.44 V and -1.0 V vs RHE, i.e., between -1.14 V and -1.5 V vs SHE, as seen in Fig. 6 and Fig. 8. The C0PC-NH2 / CNT catalyst experienced no significant deactivation during electrolysis as evidenced by the stable current profile in Fig. 9. Total cation concentration was kept at 0.1 M in all electrolytes to cancel out any cation effect (Li, J. et al., 2020, Angew. Chem., Int. Ed. Engl., 59:4464; Resasco, J. et al., 2017, J. Am. Chem. Soc., 139: 11277) in comparing CO reduction activity. All kinetic analysis was done in the potential range where the methanol production rate is lower than 10 mA cm'2to avoid mass transport influences. According to computational and experimental work in the literature (Boutin, E. et al., 2022, Chem. Eur. J., 28:e202200697; Shi, L. L. et al., 2022, Inorg. Chem., 61: 16549; Zhang, G. et al., 2022, Nat. Commun., 13:7768; Yang, D. et al., 2019, Nat. Commun., 10:677; Guil-Lopez, R. et al., 2019, Materials (Basel), 12:3902; Chang, X. et al., 2018, Angew. Chem., Int. Ed. Engl., 57: 15415), possible RDSs of CO reduction to methanol and their corresponding Tafel slopes can be summarized as follows:

[0116] Possible RDS Tafel slope pH dependent118 mV dec'1noA2 *CO+*H -> *CO(H)+* 59 mV dec1yesA3 *CO+e +H+-> *CO(H) 118 mV dec'1yes )+OH- 118 mV dec'1no* represents surface sites. *CO(H) represents that the H atom can be bonded to either O or C.

[0117] Tafel slopes for methanol production from CO reduction were determined to be all around 118 mV dec1in a wide range pH of 7.0-13.2, as seen in Fig. lOA and Fig. 1 OB, which suggested that the reaction kinetics were limited by the initial one-electron transfer process assuming a symmetry factor of 0.5. Thus, the rate-limiting chemical step (A2) involving the recombination between *CO and *H could be ruled out. On the RHE scale, the reaction rate of methanol formation increased with electrolyte pH at the same potential, and the Tafel curves exhibited clear pH-dependent shifts in potential close to -ApHX 59 mV (Fig. 10A). This indicated that the reaction rate of the RDS was not pH dependent. Consistently, the Tafel curves showed much smaller potential shifts in response to pH variation, if any, on the SHE scale (Fig. 10B). These results lead to the conclusion that the RDS and its prior steps should not involve H+. Thus, the electron transfer step (Al) and the proton-coupled electron transfer (PCET) step (A4) were viable RDS candidates.

[0118] To further confirm the RDS of methanol formation, the reaction rates in KHCO3 / H2O and KDCO3 / D2O electrolytes were compared. As shown in Fig. 10C, the formation rate of methanol at the same applied potential was severely suppressed when changing from KHCO3 / H2O to KDCO3 / D2O. Since the O-H bond has a higher zero-point energy than the O D bond, this kinetic H / D isotope effect indicates that the reaction rate is limited by proton transfer, likely from water. Thus, Al which has no proton transfer involved was ruled out. Then the PCET step (A4) was the most viable RDS that satisfied all the experimental observations. The proton transfer can occur at the C or O atom of the adsorbed CO to form *CHO or *COH, respectively (Fig. 10D). The recent discovery of the direct electrosynthesis of methylamine from carbon dioxide and nitrate catalyzed by C0PC-NH2 / CNT corroborated that methanol is formed from CO2 reduction through a formaldehyde pathway (Wu, Y. et al., 2021, Nat. Sustain., 4:725). Therefore, *CHO was the more likely product of the RDS in this case.

[0119] Since the RDS of CO reduction to methanol was found to involve proton transfer, the effect of different proton donors was further investigated. Firstly, the partial current density of methanol was compared in different electrolytes at the same moderate potential of -1.35 V vsSHE (Fig. 11 A). The K2HPO4 / KH2PO4 and KHCO3 electrolytes gave significantly higher methanol current than the K2CO3 and KOH electrolytes, reflecting the effect of proton donors. It was noted that water was the sole proton donor in the latter two electrolytes, and therefore they showed quite comparable methanol rates. Further comparison revealed that KHCO3 exhibited higher activity and selectivity towards methanol formation than K2HPO4 / KH2PO4, implying that HC03‘ was a better proton donor than H2PO4’ in this case despite its larger pKavalue.

[0120] The reaction orders of methanol and H2 formation with respect to the concentrations of HCCh' and H2PO4' were then determined in the range of 0.01 M to 0.1 M, with KCIO4 added to the electrolyte when needed to maintain a constant cation strength of 0.1 M. Methanol production showed a 0.33 order dependence on [HCO3 ] throughout the entire concentration range (Fig. 1 IB), whereas a lower order of 0.22 from 0.01 M to 0.04 M and a near zero order at concentrations higher than 0.04 M were found with respect to H2PO4 (Fig. 11C). This result again showed that HCCh' was a more effective proton donor in the reaction of CO reduction to methanol compared with water and H2PO4'. The less optimal performance of H2PO4' was attributed to its capability of enhancing the HER, which displayed a 0.43 order dependence (Fig. 11C). As [HCO3 ] increased to higher than 0.2 M, H2 evolution was greatly promoted, and methanol production was consequently suppressed (Fig. 12). Therefore, 0.1 M KHCO3 was the optimal electrolyte for this reaction (Fig. 1 ID).

[0121] To determine the reaction order with respect to CO, electrolysis experiments were conducted at a constant applied potential of -1.35 V vs SHE where no apparent CO mass transport limitation occurred and the rate of methanol production was relatively high (Fig. 6A, Fig. 6B). Under the total pressure of 1 atm, the CO partial pressure (pco) was varied from 0.01 atm to 1 atm with N2 as the balance gas (Fig. 13A, Fig. 14). A plot of log( / co) vs log( co) exhibited a slope of 1.06 in the 0.1 M KHCO3 electrolyte, indicating a first-order dependence on pco. Similar results were observed in other electrolytes with different pH values (Fig. 15). This kind of pco dependence suggested a Henry type isotherm of CO adsorption on C0PC-NH2 / CNT, which was expected because the C0PC-NH2 molecules were highly dispersed on CNT surfaces and thus the site exclusion requirement in the Langmuirian isotherm had not occurred to limit the adsorption yet. The Henry type isotherm also indicated that the absolute CO coverage on the catalyst surface remains low at 1 atm CO and that increasing pco could be a promising way to further enhance methanol production (Fig. 13B).Electrolysis under High Pressure Conditions

[0122] Inspired by the mechanistic information obtained from the aforementioned kinetic studies, CO electrolysis was performed under high pressure conditions in 0.1 M aqueous KHCO3 using a two compartment electrochemical cell capable of operations with gas pressure up to 60 atm (Fig. 13C). Indeed, the high pressure considerably improved the selectivity of methanol from CO electroreduction. Fig. 13D showed the CO electrolysis results at 10 atm CO in the potential range from -0.78 V to -1.03 V. At the optimal potential of -0.98 V, methanol was produced with a remarkable FE of 84% and a partial current density of 23.5 mA cm2. It was noted that this was a record-high methanol selectivity, a two-fold increase from the highest reported value. More importantly, this resolved one of the most critical issues for methanol production from electrochemical CO2 / CO reduction and brought the reaction into the club of some other electrochemical reactions such as CO2 / CO reduction to CO, formate, ethylene and acetate which hold more promise for practical application in emission-to-fuel / chemical conversion (Dinh, C. T. et al., 2018, Science, 360:783; Xia, C. et al., 2019, Nat. Energy, 4:776; Ji, Y. L. et al., 2022, Nat. CataL, 5:251; Overa, S. et al., 2022, Nat. CataL, 5:738; Li, J. et al., 2023, Nat. Commun., 14:698; Yin, Z. et al., 2019, Energy Environ. Sci., 12:2455; Fan, L. et al., 2020, Nat. Commun., 11 :3633).

[0123] In summary, this study obtained understanding of the previously unknown mechanism of the CoPc-NFL / CNT-catalyzed reaction of electrochemical CO reduction to methanol through systematic kinetic experiments including pH dependence, kinetic isotopic effect, proton donor effect, and CO pressure dependence. The derived mechanistic information enabled the considerable improvement in FE of methanol production to greater than 80% (Fig. 16).Materials

[0124] Potassium bicarbonate (KHCO3; 99%) and AA'-dimethylformamide (DMF;99.8%) were purchased from Alfa Aesar. Potassium phosphate monobasic (KH2PO4; 99%), potassium phosphate dibasic (K2HPO4; 98%) and potassium carbonate (K2CO3; 98%) werepurchased from Acros Organics. Potassium perchlorate (KCIO4; 99%) and sodium perchlorate (NaC104; 97%) were purchased from Thermo Fisher Scientific. Potassium hydroxide (KOH; 99.99% trace metals basis), sodium bicarbonate (NaHCOs; 99.7%), Chelex 100 sodium form and Nafion solution (5 wt.%) were purchased from Sigma-Aldrich. Carbon monoxide (99.3%) Argon (99.999%) and nitrogen (99.999%) were purchased from Airgas. Multiwalled CNTs were purchased from C-Nano (product number FT9100). The carbon paper support (Freudenberg H23C6) with MPL coating was purchased from the Fuel Cell Store. The electrolyte solutions were prepared using Milli-Q water (18.2 MQ cm at 25 °C).Preparation of Electrolyte

[0125] The potassium cation concentrations of all electrolytes for the pH dependence study were kept at 0.1 M. The electrolytes with the pH values of 7.0, 8.8, 11.3 and 13.2 were prepared by dissolving 0.035 M K2HPO4 + 0.03 M KH2PO4, 0.1 M KHCO3, 0.05 M K2CO3 and 0.1 M KOH in water, respectively. The electrolyte pH was determined using an OAKTON pH Meter (Eutech instruments). The Chelex 100 resin was used to purify all electrolytes prior to electrochemical measurements. Parameters for experiments and pH measured are recorded below.

[0126] Parameters for electrolysis experiments in different electrolytes.Note that the pH values after reaction were collected from the measurements in which highest total current densities were achieved in each electrolyte. Thus, the changed pH values represent the largest fluctuation of the pH before and after reactions in each electrolyte.

[0127] pH measured for electrolyte with varied proton donor concentration.Preparation of CoPc-NHPCNT hybrid catalyst

[0128] The synthesis of C0PC-NH2 and the purification of as-purchased CNTs were carried out as detailed in previous work (Wu, Y. et al., 2019, Nature, 575:639). To prepare the C0PC-NH2 / CNT hybrid catalyst, 30.0 mg of purified CNTs and 3 mg of C0PC-NH2 were each dispersed in 30 mL of DMF via sonication to obtain a well-dispersed CNT suspension and a C0PC-NH2 solution. Then, these two dispersions were mixed, sonicated for 30 min, and stirred for 20 h. Next, the mixture was centrifuged and the precipitate was washed using DMF and ethanol until the supernatant was transparent. Finally, the precipitate was freeze-dried to obtain the final product. The actual weight percentage of Co in the hybrid catalyst was determined to be -0.67 wt.% by ICP-MS measurements, corresponding to -10 wt.% of C0PC-NH2.Preparation ofCoPc-NHPCNT electrode

[0129] An ink was first prepared by mixing 5 mg of C0PC-NH2 / CNT, 15 pL of the Nafion solution and 5 mL of ethanol followed by sonicating for 30 min. The ink solution was then drop-casted onto the carbon paper support to reach a catalyst loading of 0.4 mg cm'2. Next,the as-prepared electrode was dried using an infrared lamp and cut into individual electrodes with the dimensions of ~0.5 x 3.0 cm2(catalyst covering an area of -0.5 x 1.0 cm2).Electrocatalytic Measurement

[0130] Ambient pressure electrolysis was performed in a custom-designed H-type electrochemical cell. A piece of anion-conducting membrane (Selemion DSV, AGC, Inc.) was used to separate the cathode and anode chambers. A graphite rod (Sigma-Aldrich, 99.999%) was used as the counter electrode and a Ag / AgCl (4.0 M KC1, Pine Research Instrumentation, Inc.) was used as the reference electrode. CO gas was delivered into the cathode chamber at a flow rate of 20.0 cm3min'1using a mass flow controller (Alicat Scientific, Inc ).

[0131] High pressure electrolysis was performed in a two-compartment electrochemical cell (Gaoss Union, Inc.). Each compartment comprised of an inner Teflon chamber and a titanium shell. A platinum foil with the dimensions of 1.5 x 3.5 x 0.02 cm3(Gaoss Union, Inc.) was used as the counter electrode and a Ag / AgCl (saturated KC1, Gaoss Union, Inc.) was used as the reference electrode. Prior to electrolysis, the headspace of each compartment was purged for 5 min by delivering CO gas at a flow rate of approximately 50.0 cm3min'1. Then, CO gas was delivered into both compartments simultaneously to reach 10 atm.

[0132] Chronopotentiometry experiments were conducted to evaluate the CO electroreduction performance using a Bio-Logic VMP3 Multichannel Potentiostat. The resistance between the working electrode and the reference electrode was determined by potentiostatic electrochemical impedance spectroscopy and then compensated automatically during measurements. Potential vs the reference electrode was converted to the RHE scale using E (vs RHE) = E (vs Ag / AgCl) + 0.199 V + 0.0591 V x pH.Product quantification

[0133] Gas-phase products were quantified using a gas chromatograph (GC, SRI 8610C) equipped with a flame ionization detector (FID) and a thermal conductivity detector (TCD). H2 was quantified using TCD, while CO was quantified using FID. High-purity Ar was used as the carrier gas. Gas-phase products were accumulated in a Tedlar gas sampling bag (SKC Inc.) andsampled using a gastight syringe (Hamilton) for GC analysis. Liquid products were quantified by a Bruker AVIII 400 MHz NMR spectrometer with water suppression. NMR samples were prepared by mixing 450 pL of the electrolyte with 50 pL of 10 mM dimethyl sulfoxide (Alfa Aesar, >99.9%) in D2O (Sigma-Aldrich, 99.9%) as the internal standard. Deuterated methanol (CD3OD) concentrations were determined through headspace analysis using a Shimadzu 8050 NX Triple Quadrupole gas chromatograph-mass spectrometry system equipped with a Phenomenex Zebron ZB-WAX column. Calibration curves were obtained using fresh CH3OH aqueous solutions with different concentrations (0.1, 0.5, 1.0, 1.5 and 2.0 mM) (Fig. 17). Quantification of CD3OD and CH3OH were performed using characteristic ions of m / z 34 and m / z 31, respectively.Reactivity plot

[0134] The presented data with error bars were averages of at least three independent electrolysis experiments. In the pco dependence studies, N2 and CO were delivered simultaneously at controlled flow rates using mass flow controllers to achieve the desired CO partial pressures. The electrolyte was refreshed after each test and was sampled for NMR analysis. A single C0PC-NH2 / CNT electrode was used throughout a sequence of measurements at different CO partial pressures to eliminate variations between different electrodes.Example 2: Photoelectrochemical CO2 reduction to methanol

[0135] In this disclosure, high-performance CO2 photoelectrochemical (PEC) reduction to methanol with over 20% FE is achieved. Remarkable partial current and turnover frequency were obtained for methanol of 3.4 mA cm'2and 1.5 s'1, respectively, which stands as the highest reported in the field to date. The enhancement in performance was achieved by tailoring the microenvironment, which played a critical role in optimizing the cascade CO2 reduction to methanol process. A Si micropillar array (SMA) structure was successfully introduced, which significantly improved CO retention and increased the electrode surface area compared to planar Si. The SMA yielded a 1.6-fold increase in total current density and a 1.5-fold increase in FEMeOH compared to planar Si. To further enhance the capture and retention of CO intermediates,a superhydrophobic carbon fluoride (CFX) coating was implemented on the SMA. This superhydrophobic microenvironment led to a 2-fold increase in FEMCOH compared to the pristine SMA. The SMA-CFXconfiguration exhibited significantly higher methanol partial current density, with values 7 and 14 times greater than those observed for the SMA without CFXcoating or on planar Si, respectively. Our CFXlayer, applied using a C4F8 reactive ion, introduces a novel approach for hydrophobic coatings in CO2 reduction, surpassing conventional hydrophilic metal oxide coatings. These findings signify the importance of microenvironment tailoring and pave the way for stable and efficient PEC CO2 reduction to liquid fuels.

[0136] In prior work, a planar Si-TiCh substrate modified with a molecular linker and a hybrid catalyst of graphene oxide / cobalt phthalocyanine (CoPc) was explored (Shang, B. et al., 2023, Angew. Chem., 135:e202215213). Although this photocathode demonstrated the ability to achieve a 6-electron reduction of CO2 to methanol with a FE of 8%, the current density and stability were limited, likely due to the weak interaction between Si and GO / CoPc. Several challenges hindered the successful integration of the catalyst on Si, including stabilizing the catalyst layer on the Si surface through linking or assembly, designing an efficient catalyst loading method for optimal light transmission, passivating the native Si surface to prevent competing hydrogen evolution reactions (HER), and creating a hydrophobic local environment to tailor the selectivity towards methanol. Therefore, the interface between the Si substrate and the molecular catalyst plays a crucial role in enabling efficient electron transport from the semiconductor to the catalyst, ensuring overall system stability.Fabrication of the Si micropillars array with super-hydrophobic coating

[0137] SMA with a diameter of 3 pm, a pitch of 10 pm, and a depth of 18 pm was fabricated through photolithography (Fig. 18, Fig. 19, all pillars diameter is 3 pm unless otherwise specified). Following the Bosch deep etch, a thin carbon fluoride (CFX) layer was coated on the SMA using octafluorocyclobutane (C4Fs) plasma (Fig. 19A). Subsequently, the CNT / C0PC-NH2 catalyst was drop-casted onto the SMA-CFX(Fig. 19B-E). Due to the superhydrophobic nature of the SMA-CFXsurface, the CNT / C0PC-NH2 catalyst exhibits a preference for adhering to the Si pillars rather than the flat Si basal plane (Fig. 19C through Fig. 19E). This unique assembly pattern facilitates efficient transmission of light through theCNT / C0PC-NH2 catalyst layer, which blocks light transmission due to the high optical density of CNT.Photoelectrocatalytic performance of Si micropillars array

[0138] The performance of PEC CO2 reduction was evaluated using an H-cell with a quartz window under light illumination (150 mW cm-2, 400 nm cut-off, unless otherwise specified), as depicted in Fig. 20A. All constant-potential experiments are conducted after a mild preactivation under -0.5 V for 10 mins to obtain a stable current. The SMA-CNT / CoPc-NFb configuration demonstrated a methanol faradaic efficiency of 21% and a CO faradaic efficiency of 37%, accompanied by a photocurrent of 16.6 mA cm’2under -0.7 V applied potential (Fig. 20B). The apparent quantum yield (AQY) of the system was calculated to be 26%. However, it should be noted that part of the AQY loss could be attributed to the light absorption by CNTs.

[0139] The stability of SMA-CNT / C0PC-NH2 was evaluated under a constant photocurrent of 15 mA cm’2(Fig. 20C). Initially, the applied voltage exhibited a continuous drop within the first 20 minutes, possibly due to the dissolution of the insulating native oxide layer on Si. After the initial 20-minute activation period, a stable faradaic efficiency of 20% for methanol was achieved and maintained for 2 hours. Subsequently, the methanol faradaic efficiency decreased to 6%, accompanied by an increase in hydrogen partial current, which was attributed to the exposure of the Si surface to the electrolyte.

[0140] Comparisons of stability, partial current, faradaic efficiency, turnover frequency, and photovoltage for CO2 reduction to methanol were made among different samples (Fig. 20D), and SMA-CNT / C0PC-NH2 exhibited the best overall performance. The stable PEC methanol catalysis achieved by SMA-CNT / C0PC-NH2 for 2 hours was four times longer than our previous work with Si-TiCh-GO / CoPc, highlighting the excellent stability provided by the CFXpassivation layer compared to traditional T1O2. The methanol faradaic efficiency and partial current of SMA- CNT / C0PC-NH2 were 3 times and 17 times higher than those of planar Si-TiCh-GO / CoPc, respectively. The introduced microstructures did not affect the photovoltage, which remained around 350 mV, comparable to planar Si.

[0141] Intriguingly, when comparing SMA-CNT / C0PC-NH2 with the state-of-the-art electrocatalysis on carbon fiber paper (CFP) using CNT / C0PC-NH2, the turnover frequency (TOF) for methanol of SMA-CNT / CoPc-NFF reaches approximately 1.5 s’1, which is slightly higher than that achieved with CFP-CNT / CoPc-NFF of 1.0 s’1. This observation suggests that the catalysis mechanism for methanol is likely the same on both SMA and CFP, involving the formaldehyde pathway. The higher TOF on SMA may be attributed to the lower loading of the catalyst (0.1 mg cm’2on SMA versus 0.4 mg cm’2on CFP). The lower faradaic efficiency and partial current on SMA may also result from this lower material loading, which is crucial for facilitating light transmission in the PEC process.Effect of the interface and microenvironment tailoring

[0142] The impact of the micropillars array and CFXcoating on the catalytic process is depicted in Fig. 21. The depth and pitch of the pillars play a vital role in controlling selectivity and photocurrent (Fig. 22). Decreased methanol selectivity and a slightly drop in current density are observed in the SMA with shorter pillar depth (7 pm) due to reduced CO trapping capability and lower electrode surface area. Conversely, excessively long pillars increase the HER due to a larger exposed Si surface area. A pitch of 10 pm between the pillars exhibits the highest methanol selectivity, while a slightly lower pitch of 8 pm elevates the HER due to increased pillar numbers and exposed Si surface. Simulation results indicate that the SMA structure generates over 5 times the local CO concentration compared to planar Si.

[0143] With the CFXcoating, SMA-CNT / C0PC-NH2 exhibits a 7-fold increase in methanol partial current compared to SMA without the coating (Fig. 21A, Figure 22). In the absence of the hydrophobic CFXcoating, electrolyte penetration into the interspace of the micropillars leads to lower methanol selectivity. In summary, the CFXcoating enables a 7-fold increase in methanol partial current, while the entire SMA-CFXstructure enhances methanol activity by 17 times compared to our previous work on planar Si. These findings highlight the effectiveness of CFX- coated Si micropillars in retaining CO intermediates for their subsequent reduction to methanol near the electrode surface.

[0144] To further assess the stability of the CFXlayer, XPS analysis was conducted before and after a 4-hour PEC stability test (Fig. 21B). The SMA surface is fully covered by CFXbeforethe PEC test, with a surface Si content of only 0.31%, while carbon (C) and fluorine (F) account for 49% and 44%, respectively. The XPS Cis spectrum exhibits a high binding energy peak around 292.5 eV, indicative of fluorinated carbon. After the PEC test, the Si content slightly increases to 0.82%, while C and F remain the major surface elements (71% and 23%, respectively). The change in surface composition explains the increase in HER observed during the stability test: (1) The decrease in F content leads to lower surface hydrophobicity, and (2) The newly exposed Si may contribute to HER. It was important to note that suppressing HER on the Si surface was extremely challenging because the active sites of the molecular catalyst are less than 0.05% on the surface. Therefore, even a small fraction of exposed Si substrate in contact with the electrolyte would significantly decrease CO2 reduction selectivity. The CFXcoating on the sidewall of the Si pillar was further investigated using transmission electron microscopy (TEM). Initially, the Si pillar is sliced using focused ion beam - scanning electron microscopy (FIB-SEM), resulting in a thin layer (approximately 100 nm) with the Si-CFXlayer in the middle (Fig. 23). Energy-dispersive spectroscopy (EDS) confirmed the presence of a 40 nm F layer, attributed to CFX(Fig. 21C). Thus, it was confirmed that the CFXlayer effectively covered the Si surface (Fig. 2 ID). With the CFXcoating, the SMA exhibits an ultrahigh contact angle of up to 154°, while the CFx-free SMA shows only 10° (Fig. 2 IE). Alongside the electrocatalytic performance results, the super-hydrophobic nature of the SMA enabled effective trapping of CO intermediates between the Si pillars, thereby achieving higher methanol faradaic efficiency.Conclusions

[0145] In conclusion, the present study successfully showcased the effectiveness of microenvironment and interface tailoring on Si-based photocathodes, leading to a remarkable faradaic efficiency of over 20% for methanol production with record-high current density. The incorporation of the micropillars array structure and the superhydrophobic coating played a crucial role in enhancing the retention of CO intermediates, consequently improving the selectivity towards deeply reduced products. This work pioneers a novel route for microenvironment tailoring on semiconductor surfaces and establishes a new benchmark for photoelectrocatalytic CO2 reduction to liquid fuels using molecular catalysts. The insights gainedfrom this research hold significant promise for advancing the field and driving further developments in the quest for sustainable and efficient renewable energy production.Materials

[0146] Si wafer (3 inch) was purchased from University Wafers Inc. C0PC-NH2 was purchased from Porphychem. CNTs were purchased from C-Nano (product number FT 9100). DMF, ethanol, Nafion solution (5 wt.%) were purchased from Sigma- Aldrich. All used gases were purchased from Airgas.Fabrication of the SMA and the coating of CFx

[0147] 3-inch p-type Si wafer was first spin-coated with HMDS and AZ 1505 photoresist. Then a photo-lithography mask consisting of 3 pm holes with a pitch of 10 pm was applied to the coated wafer and exposed using SUSS MJB4 mask-aligner. The exposed wafer was then developed using AZ 400K developer and dried using nitrogen. 100 nm of Al was then e-beam evaporated onto the exposed wafer as a hard mask for etching. After the Al evaporation, the whole wafer was immersed into pure acetone to remove the photoresist and Al on the photoresist. An Al dot array of 3 pm diameter and 10 pm pitch was created. Next, the Si-Al was transferred into Oxford PlasmaPro 100 RIE chamber. An alternating SFe (etching reagent) and C4F8 (protection reagent) plasma for 60 cycles was used for a Bosch deep etch for creating the 18 pm deep pillars. Different pillars depth can be made by controlling the cycle number. The hydrophobic CFx layer was finally deposited onto the created pillars using C4F8 plasma for 15 seconds without breaking the vacuum.Fabrication of the photocathode

[0148] Firstly, the 3-inch patterned SMA wafer was cut into 1 cm x 1 cm pieces using a diamond pen. Then 10 pL of the prepared CNT / C0PC-NH2 ink was drop-casted onto the SMA for 10 times with mild nitrogen blowing. Next, the 1 cm x 1 cm SMA-CNT / C0PC-NH2 was further cut into 0.5 cm x 1 cm pieces. A tiny drop (~1 pL) of In-Ga eutectic was transferred onto the back of the piece and rubbed into the Si with scratching using a diamond pen. Finally, the back-scratchedpiece was connected to an aluminum electrical wire using silver conductive paste and copper tape. The back and edge of the as-made photocathode was then sealed with vacuum wax (Apiezon Wax W).PEC measurements

[0149] All PEC measurements were carried out in 0.1 M KHCO3 electrolyte using a custom- made H-cell. CO2 was continuously purged into the cell with a flow rate of 20 seem. A carbon rod and saturated Ag / AgCl was used as the counter and reference electrode. A 300 W Xe lamp (Newport) was used as the light source. A 400 nm cut-off filter was used to filter the UV spectrum. The illumination power was measured by a photodiode to be around 150 mW cm'2. The gas products were detected using an online-GC system, which injects 1 mL of the outlet-gas every 10 mins. After each 30 mins of electrolysis, 0.45 mL of the electrolyte was taken out of the H-cell using a syringe without letting the electrode expose to air. 50 uL D2O containing DMSO as internal standard was added to the sample and transferred into an NMR-tube for measuring the methanol concentration.The disclosures of each and every patent, patent application, and publication cited herein are hereby incorporated herein by reference in their entirety. While this invention has been disclosed with reference to specific embodiments, it is apparent that other embodiments and variations of this invention may be devised by others skilled in the art without departing from the true spirit and scope of the invention. The appended claims are intended to be construed to include all such embodiments and equivalent variations.

Claims

CLAIMSWhat is claimed is:

1. An electrolytic device for electrochemical reduction, comprising: an anode and a hybrid cathode, the hybrid cathode comprising: a cathode; a microporous layer; a cathode catalyst; a gas channel fluidly connected to the microporous layer; and an electrolyte channel fluidly connected to the cathode catalyst; wherein the cathode catalyst comprises a compound represented by General Formula (I):General Formula (I) wherein M is a transition metal; wherein Z1, Z2, Z3, and Z4are each independently CR’ or N; wherein R1, R2, R3, R4, and R’ each independently represent mono or di -substitution, or no substitution; wherein R1, R2, R3, R4, and R’ are each independently selected from the group consisting of hydrogen, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryl oxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and wherein any two adjacent substituents are optionally joined to form a ring which may optionally be further substituted.

2. The electrolytic device of claim 1, wherein M is cobalt.

3. The electrolytic device of claim 1, wherein Z1, Z2, Z3, and Z4are each N.

4. The electrolytic device of claim 1, wherein the cathode catalyst comprises a compound represented by General Formula (I) which is further represented by General Formula (II):General Formula (II), wherein R1’, R2’, R3’, and R4’ are each independently selected from the group consisting of hydrogen, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryl oxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and wherein any two adjacent substituents are optionally joined to form a ring which may optionally be further substituted.

5. The electrolytic device of claim 1, wherein the compound represented by General Formula (I) is further substituted by at least one amino group.

6. The electrolytic device of claim 1, wherein the compound represented by General Formula (I) is further substituted by at least one alkoxy group.

7. The electrolytic device of claim 4, wherein at least one of R1’, R2’, R3’, and R4’ is an amino group.

8. The electrolytic device of claim 4, wherein at least one of R1’, R2’, R3’, and R4’ is an alkoxy group.

9. The electrolytic device of claim 1, wherein the compound represented by General Formula (I) is dispersed onto carbon nanotubes.

10. The electrolytic device of claim 1, wherein the microporous layer comprises a mixture of carbon black and PTFE with an average pore size of 40 pm.

11. The electrolytic device of claim 1, wherein the cathode catalyst comprises a compound represented by General Formula (I) which is further represented by General Formula (III):General Formula (III).

12. A method for inducing an electrochemical reaction in a feed gas, comprising: providing a microporous layer configured to be substantially permeable to a feed gas; exposing a flow of the feed gas to the microporous layer; passing a quantity of the feed gas through the microporous layer to a catalyst; and inducing an electrochemical reaction in the quantity of the feed gas with the electrode and the catalyst; wherein the catalyst comprises a compound represented by General Formula (I):General Formula (I) wherein M is a transition metal; wherein Z1, Z2, Z3, and Z4are each independently CR’ or N; wherein R1, R2, R3, R4, and R’ each independently represent mono or di -substitution, or no substitution; wherein R1, R2, R3, R4, and R’ are each independently selected from the group consisting of hydrogen, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; and wherein any two adjacent substituents are optionally joined to form a ring which may optionally be further substituted; and wherein the catalyst may optionally further comprise an electrolyte.

13. The method of claim 12, wherein the feed gas comprises at least one gas selected from the group consisting of CO and CO2.

14. The method of claim 12, wherein the electrolyte is selected from the group consisting of calcium salts, chloride salts, magnesium salts, potassium salts, sodium salts, weak acids, weak bases, and combinations thereof.

15. The method of claim 12, wherein the electrochemical reaction is a 4-electron reduction of the feed gas or a 6-electron reduction of the feed gas.

16. The method of claim 12, wherein the catalyst is dispersed on an allotrope of carbon.

17. The method of claim 16, wherein the allotrope of carbon is a multi -walled carbon nanotube.

18. A method of making methanol in an electrolytic device for electrochemical reduction of a feed stream comprising either CO2 or CO: providing an electrolytic device of claim 1; providing a microporous layer configured to be substantially permeable to a feed gas; exposing a flow of the feed gas to the microporous layer; and passing a quantity of the feed gas through the microporous layer to the electrolytic device for electrochemical reduction of the feed gas to produce methanol.

19. A photoelectrode for electrochemical reduction, comprising: a silicon substrate coated with at least one polymer; and a compound represented by General Formula (I):General Formula (I) wherein M is a transition metal; wherein Z1, Z2, Z3, and Z4are each independently CR’ or N; wherein R1, R2, R3, R4, and R’ each independently represent mono or di-substitution, or no substitution; wherein R1, R2, R3, R4, and R’ are each independently selected from the group consisting of hydrogen, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryl oxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof;wherein any two adjacent substituents are optionally joined to form a ring which may optionally be further substituted; and wherein the compound is optionally deposited on a carbon allotrope.

20. The photoelectrode of claim 19, wherein the silicon substrate is a micropillar array.

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