Observed electrochemical oscillations during the oxidation of aqueous sulfur dioxide on a sulfur modified platinum electrode

► Mechanistic investigation of the catalytic oxidation of aqueous SO 2 on platinum. ► Current oscillation observed during oxidation in the potential region 0.7 < E < 1.2 V. ► Oscillation classified as electrochemical with interfacial potential essential. ► Dual pathway mechanism proposed including dithionate intermediate. ► Significant step in understanding catalytic oxidation mechanism of SO 2. The electrochemical oxidation of aqueous sulfur dioxide has been investigated on a sulfur modified polycrystalline platinum electrode. It has been found that time and potential-based current oscillations occur on a modified electrode in the oxidation region >0.7 V vs. SHE. The oscillation is specific to catalytic oxidation on sulfur modified platinum and is not observed on an unmodified electrode. Using i–R compensation techniques, the oscillation has been found to stem from electrochemical origins; the interfacial potential being an essential variable. The influence of other controllable variables including holding potential, sulfur dioxide concentration and sulfuric acid concentration have also been investigated for their effects on the oscillation. The electrochemical oscillation is explained here in part by the intermediate formation of dithionate. Two possible mechanisms, including a dual pathway mechanism, are explored.