ADSORPTION OF CO, INTERMEDIATELY FORMED IN ELECTROCHEMICAL REDUCTION OF CO2, AT A COPPER ELECTRODE

Electroreduction of CO2 at Cu electrodes in aqueous electrolytes yields CH4 and C2H4, with adsorbed CO formed as an intermediate species. The state of adsorbed CO on a Cu electrode was studied with voltammetric and chronopotentiometric measurements. Adsorbed CO severely restricts hydrogen formation. During cathodic polarisation, coverage by adsorbed CO of the Cu electrode is ca. 90% in CO-saturated electrolytes. The adsorbed CO is easily desorbed by stirring the electrolyte vigorously as revealed by chronopotentiometric measurements. The chronopotentiometric measurements also confirmed that the surface of the copper electrode is fully covered with adsorbed CO during the electro-reduction of CO2, indicating that the rate-determining step for the reduction of CO2 to hydrocarbons must include a reaction which involves the adsorbed CO. The cross-sectional area of adsorbed CO was estimated to be 39 x 10(-16) cm2, and the rate of desorption is also discussed using coulometric measurements reported previously.