The kinetics of irreversible electrochemical oxidation and reduction processes

Abstract

I. The primary mechanism of the electrolytic oxidation of Sodium Sulphite appears to be due to a direct discharge, or partial discharge, of sulphite ions. Reaction with adsorbed oxygen may occur e.g. in sodium hydroxide solution where the two processes, electron transfer and formation of adsorbed oxygen, overlap. The occurrence of a secondary reaction with adsorbed oxygen would increase the yield of sulphate. A decrease in the yield of dithionate has been observed by Glasstone when the potential of the electrode rises. The deposition of a manganese oxide film may take place in the same region as the oxidation process, which would explain the suppression of the primary mechanism and the consequent decrease in current efficiency. The intermediate formation of hydrogen peroxide does not seem probable.II. The electrolytic reduction of acetone, formic acid and pyridine has been ascribed to a. secondary chemical reaction with atomic hydrogen. A peculiar adsorption effect appears to attend the reduction of pyridine at a platinum electrode.The reduction of nitrobenzene and benzaldehyde on the other hand appears to be due to a direct electron transfer between. the reducible substance and the electrode.In the cases where concentration polarisation effects have been observed, namely sodium sulphite, nitrobenzene and benzaldehyde, it has been shown that they obey the diffusion mechanism derived by Butler and Armstrong for reversible oxidation and reduction processes.