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Abstract:
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 Epzc, and in suppression of the electrostatic effect of the electrical double layer on the direct charge transfer at E >Epzc. 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.
