The authors have studied the electrochem. oxidn. of H2SO4 on B-doped synthetic diamond electrodes (BDD) obtained by hot filament CVD on p-Si. High current efficiency for H2SO4 oxidn. to peroxodisulfuric acid can be achieved in concd. H2SO4 (>2M) at moderate temps. (8-10 Deg). The main side reaction is oxygen evolution. Small amts. of peroxomonosulfuric acid (Caro's acid) also were detected. A reaction mechanism involving hydroxyl radicals, HSO4- and undissociated H2SO4 is proposed. According to this mechanism electrogenerated hydroxyl radicals at the BDD anode react with HSO4- and H2SO4 giving peroxodisulfate. [on SciFinder (R)]