Electrochemical reactivity of aqueous SO2 on glassy carbon electrodes in acidic media

The electrochemical reactivity of dissolved SO2 on glassy carbon (GC) electrodes was studied in sulfuric and perchloric acid solutions. The surface changes accompanying voltammetric scans were analysed with the aid of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The influence of the GC pretreatment (polished versus electrochemically activated) on the oxidation of SO2 was examined. It was found that GC samples electrochemically treated so to develop a reduced graphite oxide film on the surface were more active for SO2 oxidation. The reduction of SO2 was observed to take place at potentials below 0.0 V to yield soluble sulfide species. This species was reoxidized on positive scans to form a sulfur deposit, consisting of an underlying layer of chemisorbed sulfur (161.9–162.3 eV) and an on-top layer of bulk elemental sulfur with S8-like structure (163.6–163.8 eV). Surface sulfur did not impart electrocatalytic activity for the oxidation of SO2.