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Abstract

Cyclic and rotating disc electrode voltammetry were used to examine the 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 electrocatalytic reduction prevailing at more positive potentials, and a direct reduction of the solution species at more negative potentials. However, the rate of the former pathway at Au(111) is about two orders of magnitude higher than at Au(poly). This enhancement is likely to be linked to an increased adsorption and/or the rate of the electron transfer to adsorbed species due to a better matching of the anion structure with the trigonal structure of the Au(111) surface. Two novel features were revealed, namely the catalytic effect of protons, and the inhibition of the reduction by other adsorbable species, e.g. the perchlorate anion. Both effects can be treated within the framework of a simple electrocatalytic kinetic model. In contrast, the direct reduction at Au(111) proceeds with approximately the same rate as at Au(poly). The rate of this pathway depends strongly on the factors that influence the ion distribution on the solution side of the interface, such as the excess charge on the metal or the specific ion adsorption and its hysteresis with respect to the electrode potential.