Electrochemical and Surface Studies of Carbon Dioxide Reduction to Methane and Ethylene at Copper Electrodes in Aqueous Solutions

Abstract

The electrochemical reduction of CO 2 to CH 4 and C 2 H 4 in aqueous alkaline solutions at Cu electrodes was studied under potentiostatic conditions at −2.00V vs. SCE. The current at the Cu electrodes and the rate of hydrocarbon formation were monitored as a function of time over a temperature range from 0 to 48°C. Solutions of formate, formaldehyde, and methanol, possible intermediates in the reduction process, were also electrolyzed. Surface analyses (XPS and AES) were also performed on the Cu electrodes following electrolysis to identify surface intermediates. In addition to hydrocarbon formation, a poisoning process occurred, causing a deposit of a black film on the surface of the Cu cathode. XPS and AES studies indicated that the black film was graphitic carbon, probably the result of a side reaction, the reduction of CO 2 through formate to graphite. A tentative reaction mechanism for CO 2 reduction, based upon the data here and those of previous investigators, involving the reaction path CO 2 → CO → surface ‐ bound formyl ( Cu ‐ HCO ) → surface ‐ bound methylene ( Cu = CH 2 ) → hydrocarbon products , is proposed.