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

Kinetics of the O₂ 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.