Surface electrochemistry of UO 2 in dilute alkaline hydrogen peroxide solutions

Abstract

The reaction of H 2O 2 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 UO 2 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 (UO 2 2+) species on the electrode surface. The formation of this U VI layer blocks both H 2O 2 reduction and oxidation, thereby inhibiting the potentially rapid H 2O 2 decomposition process to H 2O and O 2. Decomposition is found to proceed at a rate controlled by desorption or reduction of the adsorbed O 2 species. Reduction of O 2 is coupled to the slow oxidative dissolution of UO 2 and formation of a corrosion product deposit of UO 3· yH 2O.