The mechanisms of the copper-carbonate catalyzed oxygen evolution reaction

Copper carbonate/bicarbonate complexes are good catalysts of the oxygen evolution reaction, OER. Previous electro-catalytic studies suggested that at pH 10.8 the active intermediate is a Cu^III complex whereas at pH 6.8 the active intermediate is a Cu^IV complex. Previous pulse-radiolysis studies indicated that Cu^III complexes are the active intermediates at both pHs. To solve the source of this discrepancy, the copper carbonate/bicarbonate catalyzed OER using peroxy-mono-sulfate as the oxidant was studied. In this system Cu^IV complexes are the active intermediates. The result points out that two electron oxidants yield Cu^IV complexes and one electron oxidants yield Cu^III complexes; both types of complexes are water oxidation agents. Electrochemical processes might proceed via both mechanisms as the anode can act as a two-electron acceptor. Thus, pulse-radiolysis does not always yield the same intermediates as electrochemistry.