Thermodynamics and kinetics of upd of lead on polycrystalline silver and gold

The formation of underpotential deposition (upd) layers of lead on polycrystalline gold and silver was reinvestigated. Two peaks are observed on gold and only one on silver. On gold, the formation and removal of the upd layers are reversible, up to sweep rates of 0.4 V s(-1), while on silver, the reversibility is limited to 0.04 V s(-1), The shapes of the peaks on both metals can be explained in the framework of the Frumkin isotherm, with different interaction parameters. The conditions for mass transport involvement have been derived. Measurements can be conducted up to sweep rates of 1.0 V s(-1) in 12 mM solutions without significant involvement of mass transport limitation. On the other hand, when deposition occurs under purely mass transport limitation, the surface responds as an ensemble of ultra microelectrodes. The shape of the anodic stripping peak is independent of the surface coverage reached during deposition, and the anodic peak potential always occurs when half of the atoms initially adsorbed have been dissolved during the positive sweep. (C) 2003 Elsevier Science B.V. All rights reserved.