UPD of zinc on polycrystalline platinum in various pH solutions

Abstract

Underpotential deposition (UPD) of metal ions has been studied extensively over recent decades, since it can give wide changes in the electronic and electrocatalytic properties of the metal surface. Kolb summarized UPD phenomena up until 1978 [l], including Zn*+/Au and Zn*+/Ag, but not Zn*+/Pt (where Zn*+/M defines Zn*+ ion UPD on a substrate metal M). The UPD of metal ions on Pt has received much attention in view of an enhancement of electrocatalytic activity. In 1970, Mikuni and Takamura 121, who observed the cyclic voltammogram (CV) on Pt in the presence of Zn*+ ions, recognized an increase of the current due to the addition of Zn*+ ions in the hydrogen adsorption region in acidic solution. In the course of a study of multivalent cation adsorption on Pt [3], we found an increase of the current in the CV on Pt at the hydrogen adsorption region by the addition of Zn*+ ions in acidic solution, in agreement with ref. 2. Therefore, in this report we investigated, under various conditions, whether Zn*+ ion UPD occurs on Pt at potentials about 1 V more positive than the equilibrium potential of Zn*+/Zn.