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 the rotating disc electrode are used to study the reduction of peroxodisulfate (PDS) on Au(111) covered by surface oxides. A strong inhibition is observed, but the PDS reduction rate does not correlate with the oxide surface coverage through a simple geometric blocking factor. Evidence is provided that 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 processes. A model of the coupling based on the diffusion controlled proton catalysis of the oxide reduction is proposed and verified by numerical simulation.