ELECTROCHEMICAL REDUCTION OF HIGH-PRESSURE CO2 ON NI ELECTRODES

The electrochemical reduction Of CO2 under high pressures of CO2 was investigated on Ni electrodes. With an increase in CO2 pressure, the Faradaic efficiency for CO2 reduction was increased while that of H-2 evolution by water reduction was decreased. Current density at -1.8 V vs. Ag/AgCl did not depend greatly on CO2 pressure at 30-degrees-C. By increasing temperature, the Faradaic efficiency for hydrocarbon formation was increased, suggesting that thermal activation was needed, although the total reduction efficiency for CO2 reduction was decreased. The Faradaic efficiency for the hydrocarbon formation showed a maximum at -1.6 V (Ag/AgCl), while those for CO and HCOOH were increased with increasing cathodic polarization. The weight distribution of hydrocarbons formed on Fe, Co, and Ni electrodes agreed well with the Schultz-Flory distribution, indicating that hydrocarbons were formed via a mechanism similar to a Fischer-Tropsch reaction for thermal catalysis, i.e., polymerization of surface carbene groups (-CH2-) produced by the reduction of CO which was formed by CO2 reduction.