Interpretation of the potentiodynamic response during the underpotential deposition of silver on polycrystalline gold

A potentiodynamic study was made of the underpotential deposition (UPD) of silver on gold using the rotating ring-disk electrode technique. The implications of analyzing the potentiodynamic data without subtracting the residual charging currents are examined. Our interpretation of the dynamic electrosorption valency data is consistent with a simple relationship between the negative shift in point of zero charge, UPD coverage and the underpotential shift. Furthermore, under equilibrium conditions, the charging current accompanying potential scan can be related quantitatively to this predicted pze shift. The potentiodynamic disk current peak structure can be interpreted in terms of the adsorption isotherm by making use of concurrent mass flux data obtained from ring electrode shielding data. Generally, complicating factors such as deposition kinetics, double layer changes and parallel chemisorption processes prevent the analysis of current-potential data obtained at a single electrode in the absence of independently obtained mass flux data. Kinetic models that involve the coupling of mass transport, adsorption and charge transfer are analyzed. A mixed control model involving charge transfer, adsorption and mass transport agrees with experimental results.