Electrocatalytic process of CO selectivity in electrochemical reduction of CO 2 at metal electrodes in aqueous media

Abstract

Electrochemical reduction of CO 2 at metal electrodes yields CO, HCOO −, CH 4, C 2H 4, and alcohols in aqueous media. Metal electrodes are roughly divided into two groups, CO formation metals (Cu, Au, Ag, Zn, Pd, Ga, Ni, and Pt) and HCOO − ones (Pb, Hg, In, Sn, Cd, Tl). Foreign atom modified electrodes (the coverage is virtually unity) showed variable product selectivity between CO and HCOO −, which depends upon the combination of modifier atom and substrate electrode. Critical investigation of foreign atom modified electrodes derived a series of CO selectivity, as Au > Ag > Cu > Zn > Cd > Sn > In > Pb > Tl > Hg. The electrode potentials of CO 2 reduction are well correlated with the heat of fusion of metals and the potential of H 2 evolution. The order of CO selectivity agrees roughly with that of the electrode potential of CO 2 reduction, and is rationalized in terms of stabilization of intermediate species CO − 2 at the electrode surface. CO is produced from stably adsorbed CO − 2, and HCOO − is formed from free or weakly adsorbed CO − 2.