Electrochemical studies of tin in zinc chloride-1-ethyl-3-methylimidazolium chloride ionic liquids

The electrochemistry of tin at polycrystalline tungsten and at glassy carbon (GC) electrodes was investigated in acidic and basic zinc chloride-1-ethyl-3-methyl-imidazolium chloride (ZnCl2-EMIC) ionic liquids at 90 degreesC. The electrodissolution of Sn produces a Sn(II) solution, which can be either oxidized to Sn(IV) or reduced to Sn metal. The formal potentials of the Sn(II)/Sn(0) couple in the 40.0-60.0 and 25.0-75.0 mol % ionic liquids are 0.25 and -0.24 V, respectively, vs. Zn(II)/Zn in a 50.0-50.0 mol % ionic liquid. The formal potentials of the Sn(IV)/Sn(II) couple in the 40.0-60.0 and 25.0-75.0 mol % ionic liquids are 0.78 and 0.29 V, respectively. The electrodeposition of Sn from Sn(II) at both electrodes is complicated by nucleation. Experimental current-time transients recorded at these electrodes are in good agreement with the theoretical model based on 3D nucleation. Sampled-current voltammograms constructed from chronoamperometric experiments indicated that the reduction of Sn(II) to Sn metal in the acidic ionic liquid is hindered by the adsorption of Sn(II) at tungsten, nickel, and GC electrodes. In the acidic ionic liquid, the adsorption of Sn(II) also hindered the voltammetric oxidation of Sn(II) to Sn(IV) at the tungsten electrode but not at the GC electrode. In the basic ionic liquid, however, the adsorption of Sn(II) at these electrodes is not observed. When the deposition potential was extended to the range where Zn(II) reduction occurred, coatings of Sn-Zn codeposits could be obtained. The Sn-Zn codeposits consist of a two-phase mixture of Sn and Zn. The effects of deposition potential and Sn(II) concentration on the Sn-Zn codeposits composition were investigated. (C) 2003 The Electrochemical Society.