The Kinetics of Indium Electroreduction from Chloride Solutions

The electroreduction of indium on indium electrode (99.98%) in perchlorate-containing chloride electrolytes is studied by the methods of linear sweep and cyclic voltammetry, impedance spectroscopy, and chronoamperometry. The indium electroreduction is limited by diffusion, the reaction rate constant is 1.3 10^–4 cm/s at the indium salt concentration of 0.1 M. The values of the apparent rate constant for the charge transfer stage found by linear sweep and cyclic voltammetry and also by impedance spectroscopy are 2.37 × 10^–3, 3.62 × 10^–3, 3.06 × 10^–3 cm/s, respectively. The values of diffusion coefficient of indium(III) ions calculated according to the Cottrell equation based on chronoamperametric measurements and from the Warburg impedance found by impedance spectroscopy are in good agreement. The presence of the Gerischer impedance is stated, which suggests that a homogeneous reaction of formation of indium chloride complexes proceeds and its mechanism is chemical-electrochemical.

     

Electrochemical deposition of indium: nucleation mode and diffusional limitation

the electrochemical deposition of indium metal from InCl₃ solutions was investigated. Cyclovoltammetric experiments showed that the initial hydrogen evolution reaction, observed together with the metal deposition on Pt surface, is blocked when the surface is covered by In. At large cathodic potentials, the current is diffusion-limited. The scan rate dependence of cyclovoltammograms allowed the determination of the diffusion coefficient of In³⁺ ions, 8.18 × 10^–6 cm²/s, using the Delahay equation. The activation energy of diffusion, determined from the temperature dependence of cyclovoltammograms, is about 0.3 eV (23 kJ/mol). Chrono-amperometric experiments are consistent with the cyclovoltammetry; the In³⁺ diffusion coefficient determined using the Cottrell law is in good agreement with the value determined by the Randles-?ev?ik equation. Moreover the use of the nucleation models developed by Scharifker and Hills showed a progressive nucleation mode. Electron microscopy observations and X-ray diffraction patterns confirmed the formation of crystalline indium deposits.