Md. Quaiyyum et al., UNDERPOTENTIAL DEPOSITION OF ZN(2+) IONS ON PLATINUM, PALLADIUM AND GOLD AT VARIOUS PH VALUES, Journal of electroanalytical chemistry [1992], 373(1-2), 1994, pp. 61-66
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.