ORIGIN OF ELECTROCATALYSIS IN THE REDUCTION OF PEROXODISULFATE ON GOLD ELECTRODES

Stationary and rotating disc electrode voltammetry are employed to stu dy the kinetics of the peroxodisulfate reduction to sulfate on Au(110) and Au(111) electrodes in the perchloric acid solution. The surface a nd the interfacial structure of these electrodes are examined by ex-si tu STM and impedance measurements, respectively. Strong adsorption of peroxodisulfate and/or sulfate on both surfaces is observed, which has the superequivalent character, and which is controlled mainly by the charge on the metal. The surface structure and symmetry of the Au(111) surface allows for a more effective overlap of the electronic wave fu nctions of the metal and the adsorbed peroxodisulfate, which results i n a two order of magnitude faster electron transfer than on Au(110). O n negatively charged surfaces, the rate of this electrocatalytic pathw ay is limited by the decreasing surface concentration of peroxodisulfa te, while the rate of the electron transfer to the solution species (t he direct pathway) can be measured. Its correction for the double laye r effect reveals that the true kinetic parameters of the direct pathwa y have essentially the same values for both electrodes. A comparison o f the kinetic behaviour of the flame-annealed and non-annealed Au(111) electrodes throws some light on the role of the steps on the metal su rface. (C) 1997 Elsevier Science S.A.