A Ring−Disk Study of the Competition between Anodic Oxygen-Transfer and Dioxygen-Evolution Reactions

Voltammetric data obtained at a rotated ring-disk electrode for oxidation of dimethyl sulfoxide (DMSO) to dimethyl sulfone support the conclusion that anodic O-transfer and O(2)(aq)-evolution reactions are in competition for a common reaction precursor. That species is concluded to be the adsorbed OH radical generated by anodic discharge of H(2)O. Because of this competition, an increase in the flux of the reactant in the O-transfer reaction causes a decrease in the rate of O(2)(aq) evolution. Therefore, difference voltammetry and hydrodynamically modulated voltammetry cannot be considered reliable for accurate deconvolution of the total electrode current resulting from these concomitant processes. A simple mathematical model is developed to describe the total current resulting from these simultaneous processes, and results of preliminary tests of this model are in good agreement with experimental data for DMSO oxidation.