Reduction of CO 2 and CO to methane on Cu foil electrodes

Abstract

The electrochemical reduction of CO 2 has been studied on Cu foil electrodes in 0.5 M KHCO 3, pH 7.6. The highest methane formation rates at 22 and 0°C were 8×10 −5 (17 mA cm −2) and 1.1×10 −4 (23 mA cm −2) mol cm −2 h −1 at −2.0 and −2.3 V vs. SCE respectively. The onset potentials for both methane and ethylene were −1.5 to −1.6 V vs. SCE. It was demonstrated that CH 4 is formed from CO at a 50 times lower rate than from CO 2 with an onset potential of −1.5 to −1.6 V vs. SCE. The methane formation rate is higher if the surface is prepared by cleaning with HCl rather than HNO 3 or oxidation in air. Tafel slopes for the methane partial current were 174 and 110 mV/ decade for the HNO 3 and HCl pretreatment respectively. Electrochemically assisted dissociation of adsorbed CO by electron transfer is suggested as the rate determining step.