The anodic oxidations of SO32-, S2O32-, and S2O42- Were examined at pure and doped PbO2-film electrodes at 25 and 65-degrees-C in a NaHCO3/Na2CO3 buffer (pH 10). Values of half-wave potentials (E1/2) vary only slightly with the identity of dopant. The numbers of electrons transferred in the electrochemical processes (n, eq mol-1), as determined by coulometry and hydrodynamic amperometry, are consistently less than expected for complete oxidation to sulfate (SO42-). Estimated values of heterogeneous rate constants and reaction orders are also compared. Results of wet-chemical analyses are interpreted to indicate that some dithionate (S2O62-) is formed during the anodic reactions. A possible mechanistic scheme based on anodic transfer of oxygen is considered.
