Energy storage by the electrochemical reduction of CO2 to CO at a porous Au film

We have investigated the performance of a porous Au film electrode for future applications in energy storage by the reduction of CO2 to CO. The electrode consists of a porous hydrophilic polymer membrane with a 260 nm Au film, applied by vapour deposition. The hydrophilic property of the polymer substrate was necessary for obtaining current densities comparable to those at an ordinary Au electrode under similar conditions: aqueous KHCO3, ambient temperature and approximately one atmosphere pressure of CO2. At potentials more negative than the activation potential for CO2 reduction, −1.2 V versus SCE, the current density was of fractional order with respect to the CO2 pressure, indicating the involvement of an adsorbed reaction intermediate, possibly a radical anion complex (CO2)2−. Analysis by GC and FTIR of the gas reaction product showed that the energy storage efficiency was maximal near the activation potential. Close to this potential, CO was formed with a Faradaic efficiency of 75% and an enthalpic efficiency of 35%. Under these conditions, the power storage capacity of the electrode was 50 W m−2.