ELECTROCHEMICAL REDUCTION OF CARBON-DIOXIDE UNDER HIGH-PRESSURE ON VARIOUS ELECTRODES IN AN AQUEOUS-ELECTROLYTE

The electrochemical reduction of CO2 at a pressure of 30 atm on various electrodes at large current densities (163-700 mA cm(-2)) in an aqueous KHCO3 solution and the cathodic voltammograms obtained were investigated. The electrocatalytic activities of various electrodes for the electrochemical reduction of CO2 under high pressure conditions were clarified. The main products on Ag, Au, Zn, Pb and In electrodes were formic acid and/or CO, as at CO2 pressures of 1 atm. The total current density on the cathodic voltammograms of those metal electrodes increased with increasing CO2 pressure. On group 8-10 metals, such as Fe, Co, Ph, Ni, Pd and Pt, the main reduction products were formic acid and/or CO under high pressure, whereas under 1 atm CO2 hydrogen was formed by reduction of water. In these cases, the total current density changed only slightly with increasing CO2 pressure. By comparing the electrocatalytic activities of various electrodes at a CO2 pressure of 30 atm with those at a CO2 pressure of 1 atm, the electrodes were classified into four groups. On Rh, Ag and Pd electrodes, the maximum partial current densities for CO2 reduction under 30 atm were 237 mA cm(-2), 383 mA cm(-2) and 397 mA cm(-2) respectively. The reduction of CO2 at large current densities could be accomplished at high pressures.