Electrochemical Reduction of Carbon Dioxide at a Platinum Electrode in Acetonitrile-Water Mixtures

Electrochemical reduction of at a platinum electrode was studied in 0.1 M tetraethylammonium perchlorate acetonitrile‐water mixtures at constant current density of . Pt, inert in the electrochemical reduction of in aqueous media, can reduce mainly to oxalic acid in water free acetonitrile. With the increase of water concentration, oxalic acid formation dropped and the yield of formic acid increased. reduction was suppressed and hydrogen evolution prevails with further increase of water concentration. The presence of adsorbed CO was confirmed on the Pt electrode surface by in situ Fourier transform‐infrared reflection absorption spectroscopy in the electrolyte. The molecular ratio in the electrolyte solution apparently determines whether or not is reduced at the CO covered Pt electrode. The product selectivity was compared with the results obtained from Pb and Au electrodes. The CO covered Pt electrode behaves like the Pb electrode, giving oxalic acid as the major product in acetonitrile with low water concentration, whereas the Au electrode yields CO. The electrocatalytic property of CO covered Pt in reduction is discussed in connection with the adsorbability of formed in the initial step of reduction as previously proposed by the present authors. The solubility of in acetonitrile‐water mixtures, measured by neutralization titration, is also presented.