The electrochemical reduction of hydrogen peroxide on uranium dioxide under intermediate pH to acidic conditions

• Published in: Electrochimica acta 2008-07, Vol.53 (18), p.5675-5683
• Main Authors: Keech, P.G., Noël, J.J., Shoesmith, D.W.
• Format: Article
• Language: English
• Subjects: Applied sciences; Corrosion; Exact sciences and technology; Hydrogen peroxide reduction; Nuclear waste disposal; pH effect; Pollution; Radioactive wastes; Uranium dioxide; Wastes
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2008.03.008

The cathodic reduction of H 2O 2 has been studied at rotating SIMFUEL disc electrodes in sodium chloride solutions over the pH range 1–9. The surfaces were analyzed by X-ray photoelectron spectroscopy. The mechanism and rate of reduction did not change over the pH range 4–9. Within this pH range, H 2O 2 chemically oxidizes the UO 2 surface to U V which is subsequently electrochemically reduced. The U V state is incorporated into a surface layer of UO 2+ x . For pH values below 3, reduction is catalyzed by the chemical creation of an adsorbed U V state. For solutions from pH 3 to 9, currents rise to the diffusion-limited value at sufficiently negative potentials since the rate of formation of U V (in UO 2+ x ) is sufficiently rapid, and the U V state formed is sufficiently stable, that reduction is never limited by the availability of this state. However, the U V state formed in acidic solutions (pH 1, 2) is less stable and can be further oxidized to the insulating U VI state prior to its dissolution as UO 2 2+, or cathodically reduced at less negative potentials than required in neutral solutions. This instability limits the availability of the catalytic state and the currents are always well below the diffusion-limited value.