Nickel Electrodeposition on a Gold Polycrystalline Foil: A Combined Voltammetric and Photoelectron Spectroscopy Study

Abstract

Cyclic voltammetry (CV) and X-ray and UV photoelectron spectroscopy (XPS, UPS) were employed to study the electrochemical deposition and dissolution of nickel on a polycrystalline gold electrode, in a 0.1 M NiSO4 electrolyte. The modification of the Ni/Au interface upon thermal treatment in ultrahigh vacuum was also investigated. Depending on the applied potential, two distinct Ni chemical states were observed. At −0.5 V versus SCE an oxidized Ni phase, mainly Ni(OH)2, was formed, whereas at potentials lower than −0.8 V nucleation of reduced Ni species surrounded by hydroxidized nickel occurred. The systematic investigation of the adsorbate species binding energies as a function of the applied potential revealed that hydroxidized nickel precipitates on the gold electrode, while reduced nickel species directly deposit on the electrode surface via the reduction of Ni2+ ions. Heating the Ni/Au interface to 650 K decomposes the adsorbed nickel film forming a new compound containing a Au−Ni intermetallic component.