Reduction of peroxodisulfate on gold(111) covered by surface oxides: inhibition and coupling between two oxide reduction processes

Cyclic voltammetry and potentiostatic current transient measurements with t he rotating disc electrode are used to study the reduction of peroxodisulfa te (PDS) on Au(111) covered by surface oxides. A strong inhibition is obser ved, but the PDS reduction rate does not correlate with the oxide surface c overage through a simple geometric blocking factor. Evidence is provided th at the inhibition is related to the coverage of Au(111) by the more stable oxide, which blocks the PDS reaction sites located probably on the surface step edges. The difference between the kinetics of the reduction of the two main oxide species on Au(111) is ascribed to a coupling between the two pr ocesses. A model of the coupling based on the diffusion controlled proton c atalysis of the oxide reduction is proposed and verified by numerical simul ation. (C) 2001 Elsevier Science B.V. All rights reserved.