The oxidn. of benzoic acid has been performed on boron doped diamond electrodes supported on silicon substrate. The voltammetric behavior has shown that during the oxidn. of benzoic acid at 2.7V (RHE), a polymeric film is formed on the electrode surface that is oxidized at higher potential values. Bulk electrolysis of benzoic acid in HClO4, under galvanostatic conditions results in an instantaneous current efficiency(ICE) near 100% at low current densities and high benzoic acid concns. Electrolysis at high current densities and low benzoic acid concns. results in a decrease of ICE due to mass transport limitations. [on SciFinder (R)]