The promoting effect of water on the electroreduction of CO sub(2) in acetonitrile

The promoting effect of water on the electrochemical reduction of carbon dioxide (CO sub(2)) from non-aqueous solvents has been studied by means of cyclic voltammetry and in-situ surface-enhanced infrared absorption spectroscopy (SEIRAS). CO sub(2) electroreduction on gold is known to be highly selective towards CO formation in aqueous and in non-aqueous media. The use of non-aqueous solvents is advantageous due to the significantly increased solubility of CO sub(2) compared to aqueous systems. However, in the absence of any proton source, extremely high overpotentials are required for the CO sub(2) electroreduction. In this work, we demonstrate for the first time a tremendous accelerating effect of water additives on the electroreduction of CO sub(2) taking place at gold/acetonitrile interfaces. Already moderate amounts of water, in the concentration range of 0.5 to 0.7 M, are sufficient to decrease significantly the overpotential of CO sub(2) reduction while keeping the CO sub(2) concentration as high as in the pure acetonitrile. The effect of water additives on the mechanism of CO sub(2) electroreduction on gold is discussed on the basis of electrochemical and IR spectroscopic data. The results obtained from gold are compared to analogue experiments carried out on platinum.