ELECTROCHEMICAL REDUCTION OF CARBON-DIOXIDE IN WATER - ANALYSIS OF REACTION-MECHANISM ON RUTHENIUM-TITANIUM-OXIDE

Mixed ruthenium/titanium oxide electrodes were prepared by thermal decomposition of the halides on titanium sheets. The electrocatalytic activity of the metallic conductive electrodes towards hydrogen evolution and carbon dioxide reduction was investigated in aqueous solutions with rotating-disk electrodes. Current-voltage curves at pH = 4 to 7 show a current-limiting behavior at small overpotentials for hydrogen evolution. In the presence of carbon dioxide, the current efficiency for CO2 reduction reaches a maximum under current-limiting conditions for hydrogen ion reduction, before a steep onset of hydrogen evolution takes place due to the reduction of water. An analysis of the electrode kinetics for the formation of reaction intermediates is given which suggests that the surface recombination of adsorbed hydrogen with CO2 is the rate-limiting step in the electrochemical reduction of CO2.