ELECTROCHEMICAL REDUCTION OF CO2 AT AN ACTIVATED SILVER ELECTRODE

The electrochemical reduction of CO2 to CO in aqueous NaClO4 solution saturated with CO2, at polycrystalline Ag cathodes was investigated as a function of the potential, temperature and electrolysis duration. A poisoning process has been found to occur in parallel with the CO formation. Building-up of the surface species closely similar to the detected poison has been observed at a Ag electrode immersed (at open-circuit) in a solution containing small amounts (10(-4) mol dm-3) of formaldehyde. A periodic anodic stripping of these inhibiting species was shown to produce stable current densities and faradaic efficiencies of CO over 4-5 h electrolysis runs. A tentative reaction pathway for CO2 reduction to CO, taking into account the experimentally determined onset potential, is proposed.