Oxidation of Sulfur Dioxide in Sulfur‐Modified Platinum‐Graphite Packed Bed Electrodes

Abstract

The oxidation of dissolved sulfur dioxide at platinum supported in porous graphite sheet electrodes was investigated between 450 and 750 mV (RHE) using a variety of platinum loadings and SO2 concentrations. Controlled reductive pre-treatment of these porous electrodes in the presence of SO2 was found to produce catalytic effects which resulted in en-hanced steady-state oxidation currents due to formation of a sulfur-modified platinum surface. In hybrid cells with fuel cell-type oxygen gas diffusion cathodes operating in the electrogenerative (galvanic) mode, the pretreated platinum-graphite anodes were used to oxidize 3-500 mM SO2 in 3M H2SO4. Performance of the anodes, which contained 0.3-18 mg Pt/cm 2, was shown to be consistent with kinetic control by a mechanism similar to those postulated from earlier studies of the reaction at bulk platinum. Pretreatment appears to enhance the rate of the electron transfer steps without affecting that of a preceding chemical step. The pretreatment effect is not limited to graphite-supported platinum electrodes and seems to be general for SO2 oxidation at high surface area platinum anodes. The electrochemical oxidation of sulfur dioxide is of practical interest because of potential applications such as waste gas clean-up with sulfuric acid recovery (1-4) and possible use in energy conversion cycles (5, 6). Work here