UNDERPOTENTIAL DEPOSITION OF ZN(2+) IONS ON PLATINUM, PALLADIUM AND GOLD AT VARIOUS PH VALUES

The underpotential deposition (UPI)) of Zn2+ ions on Pt, Pd and Au was observed in solutions at various pH values. The UPD peak potential on Pt and Pd shifted to more positive potentials with increase in Zn2+ i on concentration, the shift being 85-95% of the equilibrium shift of t he Nernst equation for Zn2+ + 2e- = ZD. This suggests that the peak is due to UPD of Zn2+ ions and is associated with electron charge transf er of ca. 2. With Au, the shift of UPD peak potential with change in Z n2+ ion concentration varied with the change in pH and the electron tr ansfer numbers were 1.5 and 2 at pH 5.0 and 6.0, respectively. The UPD shift for Zn2+-Pt and Zn2+-Pd systems was approximately the same, bei ng ca. 1.0 V at pH 0.69-6.9. whereas that for Zn2+-Au was ca. 0.6 V. T he half-width of the UPD peak increased with increase in pH: the inter action parameter of the Temkin adsorption isotherm was estimated as be ing repulsive for UPD of Zn2+ on Pt and Pd.