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

The underpotential deposition (UPD) of thallium on electropolished cop per electrodes was examined in aqueous solutions of chloride, perchlor ate and sulphate base electrolytes. Two distinct UPD peaks were observ ed and their respective charges of formation are reported. The depende nce of the peak potential E(p), the peak pseudocapacitance C(p) and th e peak half-width DELTAE1/2 for the first monolayer UPD peak were anal ysed in detail according to the method proposed by Conway and coworker s. The role of different anionic effects on the adsorption mechanism o f formation of the first monolayer is described. Analyses of cyclic vo ltammetry data and current-time transients obtained by potentiostatic pulse techniques suggest that the second UPD peak is formed by an inst antaneous nucleation and growth mechanism. Results of the pH effects o n 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 hind er the full monolayer underpotential deposition of thallium.