FTIR SPECTROSCOPY STUDY OF THE ELECTROCHEMICAL REDUCTION OF CO2 ON VARIOUS METAL-ELECTRODES IN METHANOL

The electrochemical reduction of CO2 on Sn, Cu, Au, In, Ni, Ru and Pt electrodes in methanol containing 0.1 M sodium perchlorate was studied by cyclic voltammetry and in-situ FTIR spectroscopy. Dissolved CO2 increases the cathodic current at potentials below - 1.3 V vs. Ag\0.01 M Ag+ with Sn, Au, Cu, In and Ni electrodes. It is concluded from the FTIR spectra obtained that there is no reduction of CO2 on any of the metals studied, and that the only reaction product detected by Fourier transform (FT) IR spectroscopy, i.e. CO32-, is formed by reaction of CO2 with hydroxyl anions produced in the electroreduction of residual water. In order to identify the electroreduction products of CO2 it was necessary to obtain the FTIR spectra of sodium oxalate and sodium carbonate in methanol. They were obtained by the electroreduction of oxalic acid and the alkalinization of CO2-saturated methanol respectively. It could be proved that the electroreduction of carboxylic acids to carboxylate anions in organic solvents does not require either a H-chemisorbing metal electrode, or the presence of water in the solvent.