Electrochemical behaviour of benzoic acid on platinum and gold electrodes

A voltammetric and spectroscopic study of the adsorption and oxidation of benzoic acid on platinum and gold electrodes has been carried out in acid medium. The oxidation of benzoic acid depends on the surface structure of the platinum electrode. Benzoic acid is adsorbed through the carboxylate group in a twofold coordination at potentials above 0.4 V/RHE on platinum electrodes and above 0.5 V/RHE on a gold electrode. However, at lower potential it is adsorbed through the aromatic ring. The analysis of the potential dependent band center frequencies and integrated band intensities indicates that lateral interactions between adsorbed benzoate anions are responsible for the frequency shift observed with increasing potential. On platinum electrodes benzoic acid is reduced to cyclohexanecarboxylic acid at low potentials and is oxidized to CO2, quinones, and lactones, similarly to other aromatic compounds such as benzene. On gold electrodes, it is oxidized mainly to CO2.