Effect of cadmium and lead adatoms on the reduction kinetics of peroxodisulfate anions at platinized platinum in acid solutions

The reduction of peroxodisulfate anions on a rotating Pt/Pt disk electrode in solutions of sulfuric and perchloric acids with or without cadmium and lead salts is studied. At Er > 0.2V (RHE) the reduction rate in HClO4 exceeds that in H2SO4, but at Er < 0.2V, the process in HClO4 is strongly inhibited upon approaching Er = 0. Lead adatoms catalyze the process, while cadmium adatoms inhibit it in H2SO4 and accelerate it at Er < 0.2V in HClO4. The results are interpreted by taking account of the specific adsorption of sulfuric-acid anions and their co-adsorption with cadmium cations, as well as the adsorption of peroxodisulfate anions on the Pt surface modified by lead and cadmium ions in perchlorate solutions.