UNDERPOTENTIAL DEPOSITION OF THALLIUM(I) ON ELECTROPOLISHED COPPER IN AQUEOUS-SOLUTIONS

The underpotential deposition (UPD) of thallium on electropolished copper electrodes was examined in aqueous solutions of chloride, perchlorate and sulphate base electrolytes. Two distinct UPD peaks were observed and their respective charges of formation are reported. The dependence of the peak potential E(p), the peak pseudocapacitance C(p) and the peak half-width DELTAE1/2 for the first monolayer UPD peak were analysed in detail according to the method proposed by Conway and coworkers. The role of different anionic effects on the adsorption mechanism of formation of the first monolayer is described. Analyses of cyclic voltammetry data and current-time transients obtained by potentiostatic pulse techniques suggest that the second UPD peak is formed by an instantaneous nucleation and growth mechanism. Results of the pH effects on the main UPD peak of Tl on Cu are presented and it is shown that, at high pH values, the formation of copper oxide/hydroxide does not hinder the full monolayer underpotential deposition of thallium.