Use of Underpotential Deposition for Evaluation of Overpotential Deposition Kinetics of Reactive Metals

Abstract

The underpotential deposition (UPD) of Zn onto Pt is shown to produce an electrode surface which is suitable for the evaluation of Zn overpotential kinetics. The UPD of Zn onto polycrystalline Pt was characterized in acidic and neutral sulfate solutions using voltammetric charge measurements and X-ray photoelectron spectroscopy. The charge density for UPD Zn deposition on platinum from neutral sulfate solution was estimated to be consistent with a monolayer. The decrease in evolution rates provided further evidence of the formation of Zn UPD layer. Evidence for the formation of a Zn-Pt alloy, resulting from polarization of the Pt electrode at a potential between the Zn UPD and overpotential deposition potentials is also presented. The alloy was oxidized at the same potential as the Pt substrate, illustrating the large interaction between Zn and Pt due to the small crystallographic misfit. The alloy also decreased evolution rates, relative to the Pt substrate. The use of such a modified substrate for measurement of kinetic parameters for metal deposition is described and the results obtained are shown to compare favorably with the literature values. © 2003 The Electrochemical Society. All rights reserved.