Surface electrochemistry of UO2 in dilute alkaline hydrogen peroxide solutions

The reaction of H₂O₂ on SIMFUEL electrodes has been studied electrochemically and under open circuit conditions in 0.1 mol l⁻¹ NaCl (pH 9.8). The composition of the oxidized UO₂ surface was determined by X-ray photoelectron spectroscopy (XPS). Peroxide reduction was found to be catalyzed by the formation of a mixed U^IV/U^V (UO_2+x) surface layer, but to be blocked by the formation of U^VI (UO₂²⁺) species on the electrode surface. The formation of this U^VI layer blocks both H₂O₂ reduction and oxidation, thereby inhibiting the potentially rapid H₂O₂ decomposition process to H₂O and O₂. Decomposition is found to proceed at a rate controlled by desorption or reduction of the adsorbed O₂ species. Reduction of O₂ is coupled to the slow oxidative dissolution of UO₂ and formation of a corrosion product deposit of UO₃·yH₂O.