Surface electrochemistry of UO2 in dilute alkaline hydrogen peroxide solutions: Part II. Effects of carbonate ions

The electrochemical reduction of hydrogen peroxide has been studied on uranium dioxide electrodes. The reduction kinetics are found to be influenced by dissolved carbonate/bicarbonate ions. The formation of hydrated UVI species on the electrode surface is avoided in carbonate solutions, allowing H2O2 reduction to proceed at less cathodic potentials than in carbonate-free solutions. At more cathodic potentials, the adsorption of carbonate ions on the active reduction sites inhibits the H2O2 reduction reaction. Over a narrow potential region, the reduction of peroxide is catalyzed by coadsoption of H2O2 and HCO3−/CO32−. The pH dependence of the H2O2 reduction reaction appears to be stronger in carbonate solutions than in solutions that do not contain carbonate. This can be attributed to the displacement of inhibiting CO32−/HCO3− adsorbed ions by OH−.