The silver upd on gold(111) revisited

The adsorption of silver onto Au(111) and stepped Au(111) in sulphuric acid has been investigated in the underpotential deposition (upd) region using cyclic voltammetry in combination with UHV-based methodologies. We report data showing that the first stage of silver upd is strongly dependent on the superficial state of the substrate and on the formation of a Ag–Au surface alloy. In the absence of the surface alloy, the sharp intense upd peak obtained at 0.53 V (vs. Ag+ | Ag) is associated with the deposition of Ag on Au terraces. Potential cycling in the upd region introduces some surface defects and gradually transforms the surface into a surface alloy phase leading to the appearance of a silver upd peak at 0.61 V (vs. Ag+ | Ag). An unusual temperature dependence of the kinetics of surface alloy formation is reported and explained by considering that the rate of surface alloying depends strongly on the concentration of the surface defects and that self-annealing of surface defects takes place. In the light of these findings, voltammetric data from previous studies of silver on Au(111) are discussed.