Electrochemical study of cadmium in acidic zinc chloride-1-ethyl-3-methylimidazolium chloride ionic liquids

The electrochemistry of Cd(II) was studied with voltammetry and chronoamperometry at polycrystalline Pt, Ni, and W electrodes in the acidic zinc chloride-1-ethyl-3-methylimidazolium chloride (ZnCl2-EMIC) ionic liquid. Cd(II) could be reduced to cadmium metal via a single-step quasi-reversible electron-transfer process. The redox potential of the Cd(II)/Cd couple shifted negatively as the acidity of the ionic liquid decreased. In addition, underpotential deposition of Cd was observed at Pt and Ni electrodes. This was related to the work function of these metals. Analysis of the chronoamperometric transient behavior revealed a three-dimensional instantaneous nucleation/growth process for the electrodeposition of pure Cd at both Pt and W substrates. When the deposition potential was extended to the potential range where Zn(II) reduction occurred, codeposition of Zn with Cd became possible. The dependency of the Cd-Zn codeposits composition on the deposition potential, temperature, and Cd(II) concentration was investigated. (C) 2002 The Electrochemical Society.