Irreversible oxidation of hydroxide ion in the light of negative capacitance by fast scan voltammetry

Abstract

Intermediates associated with dioxygen generation by anodic decomposition of water were detected at a thin wire platinum electrode by fast scan cyclic voltammetry. Hydroxide ion was oxidized through the diffusion-controlled one-electron transfer reaction to immediately yield hydrogen peroxide, which was detected as adsorbed species on the electrode. The anodic peak potential was almost independent of the scan rates in spite of distinctive following chemical reactions. The anodic peak current at fast scans was observed to be smaller than the diffusion-controlled one. The lower deviation failed to be explained in terms of the heterogeneous electrode kinetics. It was ascribed to the negatively capacitive current which was caused by dipoles of hydroxide ion and the counter cation. The capacitance values were invariant to the concentrations of hydroxide ion. The invariance was explained in terms of destruction of dipoles by agitation of hydroxyl radicals.