ELECTROCATALYTIC REDUCTION OF PEROXODISULFATE ANION ON AU(111) IN ACIDIC AQUEOUS-SOLUTIONS

Cyclic and rotating disc electrode voltammetry were used to examine th e electrochemical reduction of peroxodisulfate at an Au(111) electrode in acidic aqueous solutions. As for a polycrystalline gold electrode, two well-distinguished parallel pathways were observed, i.e. an elect rocatalytic reduction prevailing at more positive potentials, and a di rect reduction of the solution species at more negative potentials. Ho wever, the rate of the former pathway at Au(111) is about two orders o f magnitude higher than at Au(poly). This enhancement is likely to be linked to an increased adsorption and/or the rate of the electron tran sfer to adsorbed species due to a better matching of the anion structu re with the trigonal structure of the Au(111) surface. Two novel featu res were revealed, namely the catalytic effect of protons, and the inh ibition of the reduction by other adsorbable species, e.g. the perchlo rate anion. Both effects can be treated within the framework of a simp le electrocatalytic kinetic model. In contrast, the direct reduction a t Au(111) proceeds with approximately the same rate as at Au(poly). Th e rate of this pathway depends strongly on the factors that influence the ion distribution on the solution side of the interface, such as th e excess charge on the metal or the specific ion adsorption and its hy steresis with respect to the electrode potential.