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 (∼ 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.