Recent developments in electrochemical and photoelectrochemical CO 2 reduction: involvement of the (CO 2 ) 2 . − dimer radical anion

Electrochemical CO 2 reduction was examined on high‐area transition metal catalysts supported on nanoporous activated carbon fiber (ACF) supports, in the form of gas diffusion electrodes, in aqueous KHCO 3 solution. The most active catalyst was ACF/Ni, on which up to ca 65 mA cm −2 current density for CO production was observed, with simultaneous production of hydrogen of ca 15 mA cm −2 at −1.6 V vs SCE. At more negative potentials, higher H 2 /CO ratios can be obtained. The reaction mechanism for CO production probably involves a chemical reaction between CO 2 and the radical anion CO 2 . − to produce the CO 2 dimer radical anion (CO 2 ) 2 . − . The results are compared with those for photoelectrochemical CO 2 reduction on p‐InP, on which the mechanism is thought to involve the one‐electron reduction of two adsorbed CO 2 molecules to produce the CO 2 dimer radical anion. Copyright © 2001 John Wiley & Sons, Ltd.