Interpretation of Potentiostatic Transient Behavior during the Underpotential Deposition of Silver on Gold Using the Rotating Ring-Disk Electrode

The ring-disk electrode current responses during the UPD of Ag on Au under potentiostatic conditions were analyzed in terms of the kinetics and mechanism of the process and concurrent dynamic double layer changes. The rate of UPD occurs under mixed control of solution mass transport, surface adsorption, and charge-transfer processes. The exchange current density, charge-transfer coefficient, and adsorption coefficient were determined for various applied potentials and silver-ion concentrations. We define a dynamic electrosorption valency γd that takes into account both charge separation and leakage processes across the interface. Various components determining γd and their estimation are outlined. Dynamic changes in the double layer capacity during the UPD process were evaluated. The kinetic parameters and double layer capacitance changes suggest the formation of ordered structures at higher coverages and randomly adsorbed structures at low coverages.