Peroxodisulphate reduction as a novel probe for the study of platinum single crystal/solution interphases

The reduction of peroxodisulphate anion at platinum single crystal electrodes in HClO4 solutions has been studied by cyclic voltammetry under hanging meniscus configuration, either in quiescent solutions or under rotating disk regime. On the three platinum basal planes, the reaction only proceeds at a significant rate in a narrow potential range located around the potential of zero total charge. At higher potentials, the reaction is probably inhibited by the adsorption of intermediates produced in the stage of peroxodisulphate dissociative adsorption. At lower potentials, hydrogen adsorption or/and strong polarization of water molecules on the electrode surface is responsible for the inhibition of the reaction. A strong catalytic effect is observed when the electrode surface is modified with submonolayer amounts of bismuth, being the reduced form of bismuth the most catalytic for this reaction. The pronounced structural sensitivity of peroxodisulphate reduction on single crystalline surfaces makes it an attractive model reaction for probing the structural features of Pt/solution interface (like N2O reduction).