The electrochemical reduction of oxygen on zinc corrosion films in alkaline solutions

Kinetics of the O-2 reduction has been characterized on Zn corrosion films by Pt/Zn rotating ring-disc electrode (RRDE) and EIS methods. On zinc-oxide films a two-step reduction was identified in various buffer solutions of pH 10.5, while a small quantity of H2O2 intermediate could be detected. On the basis of results obtained from Pt/Zn and Pt/Pt RRDE experiments in solutions containing H2O2, it was further confirmed that the HO2- was reduced to OH- through the zinc-oxide corrosion layer. Capacitance data of the zinc-oxide/electrolyte interface calculated from steady-state impedance diagrams measured at various cathodic potentials indicate the presence of a space charge layer of the semi-metallic ZnO. The solid-state reaction mechanism of HO2- disproportion with participation of Zn-i(+) interstitials, oxygen ion vacancies of the non-stoichiometric Zn-oxide, and chemisorbed HO2- is discussed. (C) 2007 Elsevier Ltd. All rights reserved.