Item

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 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.