Electrochemical CO2 Reduction to Methane

Abstract

Nation-modified electrodes for the CO2 reduction reaction (CO2RR) to hydrocarbon products. Depending on the thickness of the Nation membrane and its admixture with other polymers, CO2 reduction occurs principally at the electrode-polymer interface. A Nation overlayer of 15 μm on a Cu electrode enables an extraordinarily high yield of CH4 production (88% Faradaic efficiency) at a low overpotential (540 mV). Other embodiments directed to admixtures of Nation and other polymers and/or cocatalysts, various metal substrates and electrolyte solutions which comprise an aprotic solvent in addition to a bicarbonate solution show impact on the Faradaic efficiency, yield and carbon-based products produced by the present invention.

What is claimed is: 
     
         1 . A method for CO 2  reduction, comprising:
 providing an electrode having a layer of a predetermined uniform thickness of a polymeric composition; and   placing the electrode with the layer of polymeric composition in contact with a solution effective for CO 2  reduction, wherein said polymeric composition consists essentially of Nafion polymer or an admixture of Nafion in combination with another polymer and/or a cocatalyst.   
     
     
         2 . The method defined in  claim 1  wherein the polymeric composition is Nafion or Nafion in combination with at least one additional polymer selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), polyethyleneglycol (PEG), polyvinylalcohol (PVA), polyethyleneimine (PEI), polytetrafluoroethylene (PTFE) and mixtures thereof. 
     
     
         3 . The method defined in  claim 1  wherein the polymeric composition includes a fluoropolymer. 
     
     
         4 . The method defined in  claim 3  wherein the fluoropolymer is polyvinylidene fluoride (PVDF, polytetrafluoroethylene (PTFE) or a mixture thereof. 
     
     
         5 . The method defined in  claim 2  wherein the at least one additional polymer is PDVF. 
     
     
         6 . The method defined in  claim 1  wherein the layer of the polymeric composition is Nafion having a thickness between approximately 2 μm and approximately 15 μm. 
     
     
         7 . The method defined in  claim 1  wherein the layer of the polymeric composition has a thickness effective to stabilize an intermediate in which CO is bound to the electrode coated with the layer of the polymeric composition. 
     
     
         8 . The method defined in  claim 2  wherein the layer of the polymeric composition has a thickness between approximately 20 μm and approximately 90 μm. 
     
     
         9 . The method defined in  claim 1 , wherein the electrode is made of a material selected from the group consisting of carbon, copper, nickel and zinc and mixtures and alloys thereof. 
     
     
         10 . The method defined in  claim 1 , wherein the electrode is made of a transition metal or transition metal alloy. 
     
     
         11 . The method defined in  claim 10  wherein the electrode is made of copper, zinc, silver, gold, cadmium, nickel, palladium, platinum or an alloy thereof. 
     
     
         12 . The method of  claim 10  wherein the electrode is made of copper or a copper alloy. 
     
     
         13 . The method according to  claim 12  wherein the copper alloy is brass (copper and zinc), bronze/phosphor bronze (copper and tin), naval brass (copper, zinc and tin), aluminum bronze (copper and aluminum), berylliumcopper (copper and beryllium), cupronickel (copper and nickel, and optionally iron and/or manganese), nickel silver (copper with nickel and zinc), copper silver (copper with silver) or copper gold (copper with gold). 
     
     
         14 . The method defined in  claim 13  wherein the copper alloy is brass. 
     
     
         15 . The method defined in  claim 10  wherein the layer of the polymeric composition has a thickness effective to stabilize an intermediate in which CO is bound to the electrode coated with the layer of polymeric composition. 
     
     
         16 . The method defined in  claim 1  wherein the solution is a bicarbonate solution or a bicarbonate solution further comprising an effective amount of an aprotic solvent. 
     
     
         17 . The method according to  claim 16  wherein said aprotic solvent is selected from the group consisting of acetonitrile (MeCN), dimethylformamide (DMF), dimethylacetamide DMA), dimethylsulfoxide (DMSO), tetrahydrofuran (THF), propylene carbonate (PC), or an alkyl nitrile (such as propylnitrile, butyl nitrile, adiponitrile, benzonitrile) or a mixture thereof. 
     
     
         18 . The method according to  claim 16  wherein said aprotic solvent is acetonitrile. 
     
     
         19 . The method defined in  claim 1 , further comprising conducting an electrical current through said solution to said electrode at least in part through the layer of the polymeric composition. 
     
     
         20 . The method defined in  claim 1  wherein said polymeric composition further comprises a cocatalyst. 
     
     
         21 . The method defined in  claim 20  wherein said cocatalyst is in the form of a nanoparticle or a nanowire. 
     
     
         22 . The method defined in  claim 20  wherein said cocatalyst is made of copper (metallic), cuprous oxide (Cu 2 O), cupric oxide (CuO), Zn, zinc oxide (ZnO) or silver (Ag). 
     
     
         23 . The method according to  claim 1  wherein said polymeric composition is Nafion. 
     
     
         24 . An electrode for CO 2  reduction, comprising:
 a base or body of electrically conductive material; and   a layer of a polymeric composition of a predetermined uniform thickness ranging from 1 μm to 100 μm on a surface of said base or body, wherein said polymeric composition consists essentially of Nafion polymer or an admixture of Nafion in combination with another polymer and/or a cocatalyst.   
     
     
         25 . The electrode defined in  claim 24  wherein the polymeric composition is Nafion polymer in the absence of an additional polymer or cocatalyst. 
     
     
         26 . The electrode defined in  claim 24  wherein the polymeric composition further includes polyvinylidene fluoride and mixtures thereof with Nafion polymer. 
     
     
         27 . The electrode defined in  claim 24  wherein said polymeric composition comprises at least one additional polymer selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), polyethyleneglycol (PEG), polyvinylalcohol (PVA), polyethyleneimine (PEI), polytetrafluoroethylene (PTFE) and mixtures thereof. 
     
     
         28 . The electrode defined in  claim 24  wherein the polymeric composition includes a fluoropolymer. 
     
     
         29 . The electrode defined in  claim 28  wherein the fluoropolymer is polyvinylidene fluoride (PVDF, polytetrafluoroethylene (PTFE) or a mixture thereof. 
     
     
         30 . The electrode defined in  claim 27  wherein the at least one additional polymer is PVDF. 
     
     
         31 . The electrode defined in  claim 24  wherein the layer of the polymeric composition is Nafion having a thickness between approximately 2 μm and approximately 15 μm. 
     
     
         32 . The electrode defined in  claim 24  wherein the layer of the polymeric composition has a thickness effective to stabilize an intermediate in which CO is bound to the electrode coated with the layer of the polymeric composition. 
     
     
         33 . The electrode defined in  claim 24  wherein the layer of the polymeric composition has a thickness between approximately 20 μm and approximately 90 μm. 
     
     
         34 . The electrode defined in  claim 24 , wherein the electrode is made of a material selected from the group consisting of carbon, copper, nickel and zinc and mixtures and alloys thereof. 
     
     
         35 . The electrode defined in  claim 24   24 - 33 , wherein the electrode is made of a transition metal or transition metal alloy. 
     
     
         36 . The electrode defined n  claims 24  and  35  wherein the electrode is made of copper, zinc, silver, gold, cadmium, nickel, palladium, platinum or an alloy thereof. 
     
     
         37 . The electrode according to  claim 35  wherein the electrode is made of copper or a copper alloy. 
     
     
         38 . The electrode defined in  claim 37  wherein the copper alloy is brass (copper and zinc), bronze/phosphor bronze (copper and tin), naval brass (copper, zinc and tin), aluminum bronze (copper and aluminum), berylliumcopper (copper and beryllium), cupronickel (copper and nickel, and optionally iron and/or manganese), nickel silver (copper with nickel and zinc), copper silver (copper with silver) or copper gold (copper with gold). 
     
     
         39 . The electrode defined in  claim 38  wherein the copper alloy is brass. 
     
     
         40 . The electrode defined in  claim 24  wherein said polymeric composition further comprises a cocatalyst. 
     
     
         41 . The electrode defined in  claim 40  wherein said cocatalyst is in the form of a nanoparticle or a nanowire. 
     
     
         42 . The electrode defined in  claim 40  wherein said cocatalyst is made of copper (metallic), cuprous oxide (Cu 2 O), cupric oxide (CuO), Zn, zinc oxide (ZnO) or silver (Ag). 
     
     
         43 . An electrolysis apparatus comprising: a housing defining a chamber; at least two electrodes disposed in part in said chamber and operatively connectable to a voltage source, said two electrodes including a working electrode; a first port member or fitting fixed to housing and communicating with said chamber for directing fluid into said chamber; and a second port member or fitting fixed to housing and communicating with said chamber for conveying fluid out of said chamber, said working electrode including an electrically conductive base member and a coating layer of a predetermined thickness of a polymeric composition disposed on said base member, wherein said polymeric composition comprises Nafion alone or in combination with an additional polymer and/or a cocatalyst. 
     
     
         44 - 61 . (canceled)