Kinetic studies of the oxygen—peroxide couple on pyrolytic graphite

The cathodic and anodic properties of the oxygen—peroxide couple have been studied on ordinary pyrolytic graphite, high-pressure annealed pyrolytic graphite and single crystal graphite in alkaline solutions using the rotating disk technique. Both the reduction of O2 and oxidation of peroxide are inhibited on the cleavage surface of the oriented graphite relative to the edge surface. This difference in behaviour is attributed to the lack of suitable adsorption sites on the cleavage surface for the reacting species and/or intermediates. The current/potential data, reaction orders, and stoichiometric number support the following mechanism: O2 → O2(ads); O2(ads) + HOH + e → HO2(ads) + OH−; 2HO2(ads) + OH− → HO2− + O2 + HOH, with the first and second steps rate-controlling for the cathodic reduction.