MECHANISM OF PEROXODISULFATE REDUCTION AT A POLYCRYSTALLINE GOLD ELECTRODE

The reduction of peroxodisulfate anions at a polycrystalline gold elec trode in various base electrolytes (NaF, HClO4, H2SO4) was studied by rotating disc voltammetry and the a.c. impedance technique. The reacti on proceeds via two parallel pathways: surface (catalytic) and direct charge transfer mechanisms, which involve chemically adsorbed and solu tion intermediates respectively. Specific adsorption of peroxodisulfat e, and/or of the sulfate anion produced, results in a negative shift o f the potential of zero charge E(pzc), and in suppression of the elect rostatic effect of the electrical double layer on the direct charge tr ansfer 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 f or quantitatively using the classical Frumkin correction. In both acid ic and neutral media, surface metal oxides play a minor role.