MECHANISM OF PEROXODISULFATE REDUCTION AT A POLYCRYSTALLINE GOLD ELECTRODE

The reduction of peroxodisulfate anions at a polycrystalline gold electrode in various base electrolytes (NaF, HClO4, H2SO4) was studied by rotating disc voltammetry and the a.c. impedance technique. The reaction proceeds via two parallel pathways: surface (catalytic) and direct charge transfer mechanisms, which involve chemically adsorbed and solution intermediates respectively. Specific adsorption of peroxodisulfate, and/or of the sulfate anion produced, results in a negative shift of the potential of zero charge E(pzc), and in suppression of the electrostatic effect of the electrical double layer on the direct charge transfer at E > E(pzc). On the negatively charged electrode surface, the electrostatic repulsion of peroxodisulfate anions from the electrical double layer is a significant kinetic factor which can be accounted for quantitatively using the classical Frumkin correction. In both acidic and neutral media, surface metal oxides play a minor role.