Electrochemical reduction of CO2 with high current density in a CO2 + methanol medium at various metal electrodes

Abstract

Various metals were used as working electrodes in the electrochemical reduction of highly concentrated CO2 in a CO2 + methanol medium. Reduction products were CO, CH4, C2H4 and methyl formate (HCOOCH3). Methyl formate was formed by the reaction between solvent, methanol, and a CO2 reduction product, formic acid, which corresponds to formic acid formation in aqueous systems. Basically, most electrodes gave the same principal product both in the present system and in the aqueous system. At W, Ti and Pt electrodes, CO2 reduction was inefficient. Sn and Pb electrodes were active in formate production. However, CO was formed much more efficiently in the present system than in the aqueous system. It was indicated that Sn and Pb served as electrodes catalyzing formate production, while the supporting electrolyte, tetrabutylammonium cation, promoted CO formation. Electrolysis at Ag, Zn and Pd electrodes yielded CO mainly. Hydrocarbon formation at a Cu electrode was less efficient than in aqueous systems. However, hydrocarbon was formed efficiently at an Ni electrode. These differences in hydrocarbon formation in the present system, in comparison with aqueous systems, could be explained by the balance between hydrogen atom and CO2 reduction intermediates on the electrode surface.