Influence of the Electrode and Chaotropicity of the Electrolyte on the Oscillatory Behavior of the Electrocatalytic Oxidation of SO2

SO2 oxidation has been proposed as an alternative pathway for the electrochemical generation of H-2 because it requires lower potentials than water splitting and at the same time consumes an atmospheric pollutant. Theoretical predictions suggest that gold and platinum are the most active catalysts for this reaction. This work presents experimental evidence that, contrary to the predictions, SO2 oxidation starts at less positive potentials on Au electrodes (ca. 0.60 V (vs RHE)) than on Pt. It is found further that the observed current densities on Au are one order of magnitude higher than on Pt. In addition, the SO2 oxidation mechanism depends on the chemical nature of the electrolyte used: A kosmotropic anion (HSO4) results in lower currents than a chaotropic one (ClO4-), and the latter displays oscillatory reaction rates under both potentiostatic and galvanostatic regimes.