ELECTROCHEMICAL REDUCTION OF HIGH-PRESSURE CO2 AT PB, HG AND IN ELECTRODES IN AN AQUEOUS KHCO3 SOLUTION

The electrochemical reduction of CO2 under high pressure in an aqueous solution at metal electrodes with high overpotentials for hydrogen evolution such as Pb, Hg and In was studied. When the electrolysis was conducted under high pressure CO2, HCOOH was formed with faradaic efficiencies of almost 100%, even at high current densities (similar to 200 mA cm(-2)). The maximum partial current density of HCOOH formation amounted to 560 mA cm(-2) at the In electrodes under 60 atm of CO2. On the other hand, it was found that CO could form as the main reduction product of CO2 at Pb and In electrodes, at which HCOOH has previously been believed to be the main product under 1 atm of CO2. The selectivity for CO formation depended on the electrode potential. The less negative were the potentials, the higher was the faradaic efficiency of CO formation.