ELECTROCHEMICAL REDUCTION OF CO2 WITH HIGH-CURRENT DENSITY IN A CO2 PLUS METHANOL MEDIUM AT VARIOUS METAL-ELECTRODES

Various metals were used as working electrodes in the electrochemical reduction of highly concentrated CO2 in a CO2 + methanol medium. Reduc tion products were CO, CH4, C2H4 and methyl formate (HCOOCH3). Methyl formate was formed by the reaction between solvent, methanol, and a CO 2 reduction product, formic acid, which corresponds to formic acid for mation in aqueous systems. Basically, most electrodes gave the same pr incipal product both in the present system and in the aqueous system. At W, Ti and Pt electrodes, CO2 reduction was inefficient. Sn and Pb e lectrodes were active in formate production. However, CO was formed mu ch more efficiently in the present system than in the aqueous system. It was indicated that Sn and Pb served as electrodes catalyzing format e production, while the supporting electrolyte, tetrabutylammonium cat ion, promoted CO formation. Electrolysis at Ag, Zn and Pd electrodes y ielded CO mainly. Hydrocarbon formation at a Cu electrode was less eff icient than in aqueous systems. However, hydrocarbon was formed effici ently at an Ni electrode. These differences in hydrocarbon formation i n the present system, in comparison with aqueous systems, could be exp lained by the balance between hydrogen atom and CO2 reduction intermed iates on the electrode surface.