Abstract
The underpotential deposition (UPD) of Zn 2+ 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 Zn 2+ ion concentration, the shift being 85–95% of the equilibrium shift of the Nernst equation for Zn 2+ + 2e − = Zn. This suggests that the peak is due to UPD of Zn 2+ ions and is associated with electron charge transfer of ca. 2. With Au, the shift of UPD peak potential with change in Zn 2+ ion concentration varied with the change in pH and the electron transfer numbers were 1.5 and 2 at pH 5.0 and 6.0, respectively. The UPD shift for Zn 2+-Pt and Zn 2+-Pd systems was approximately the same, being ca. 1.0 V at pH 0.69–6.9, whereas that for Zn 2+-Au was ca. 0.6 V. The half-width of the UPD peak increased with increase in pH; the interaction parameter of the Temkin adsorption isotherm was estimated as being repulsive for UPD of Zn 2+ on Pt and Pd.
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