Thermodynamic properties of monolayers of silver and lead deposited on polycrystalline gold in the underpotential region

Equilibrium properties of metal monolayers such as monolayer coverage, free energy and equilibrium potential and the electrosorption valency have been determined by the ring-disk method for underpotential deposits of silver and lead on polycrystalline gold. The concept of monolayer equilibrium potential is useful in distinguishing between underpotential deposition (UPD) reactions that occur by a Faradaic mechanism and those that occur by metal-ion adsorption processes. Both the dependence of the underpotential shift on UPD monolayer coverage and the effect of solution complexation to produce anionic metal species show that no partial charge exists on the silver or lead UPD species. Anomalous adsorption isotherm parameters are due to the gradual variation of the electron work function of the substrate with UPD coverage. Dynamic electrosorption valency measurements show that conditions for a priori separability do not exist either for the Faradaic and non-Faradaic components, or the adsorption and charge separation components accompanying the UPD process.