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Abstract: The effect of Mn2+ ions on current efficiency (CE), deposit morphology and polarization behaviour during electrodeposition of zinc from acidic sulphate solutions was investigated. In the conditions studied, Mn2+ ions had no significant effect on CE over the concentration range of 1–10gdm−3. However, a decrease in CE of more than 35% was obtained at 50gdm−3. The cathodic polarization curves and the corresponding kinetics analysis demonstrated that this decrease in CE at higher concentrations of Mn2+ ions was due to the strong depolarizing effect of MnO4 − ions and other oxidized products of manganese. Moreover, the kinetics analysis of anodic polarization suggested that the presence of Mn2+ ions catalyzed the oxygen evolution reaction. The addition of Mn2+ ions was also observed to change the surface morphology and deposit quality of the electrodeposited zinc, affecting the crystallographic orientation by significantly inhibiting the growth of (002) and (100) planes. [Copyright &y& Elsevier]

The effects of temperature and current density on cathodic current efficiency, specific energy consumption, and zinc deposit morphology during zinc electrodeposition from sulfate electrolyte in the presence of 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM]HSO4) as additive were investigated. The highest current efficiency (93.7%) and lowest specific energy consumption (2,486 kWh t−1) were achieved at 400 A m−2 and 313 K with addition of 5 mg dm−3 [BMIM]HSO4. In addition, the temperature dependence of some kinetic parameters for the zinc electrodeposition reaction was experimentally determined. Potentiodynamic polarization sweeps were carried out to obtain the expression for each parameter as a function of temperature. In the condition studied, the exchange current density depended on temperature as ln( i0) = − a/ T + b and the charge transfer coefficient was constant. Moreover, the adsorption of the additive on cathodic surface obeyed the Langmuir adsorption isotherm. The associated thermodynamic parameters indicated the adsorption to be chemical. [ABSTRACT FROM AUTHOR]

Abstract: The direct electrochemical reduction of titanium dioxide (TiO2) to metallic titanium at room temperature is firstly studied in Lewis basic AlCl3–1-butyl-3-methylimidizolium (AlCl3–BMIC) ionic liquid. In this study, cyclic voltammetry, potentiodynamic polarization, sampled current voltammetry and X-ray photoelectron spectroscopy (XPS) techniques were utilized. Analysis of the cyclic voltammetry suggested that TiO2 film can be reduced to metallic Ti. The sampled current voltammetry was applied to elaborate the reduction mechanism and the results showed that this reduction process may include two steps. When the output potential difference of 2.8V was applied, a TiO2 cylindrical pellet was partly reduced to metallic Ti. However, due to the very slow reaction rate, there was only about 12wt% of TiO2 was reduced during the electrolysis time of 48h. It was predicted that the process for the direct reduction of solid TiO2 would be explained as follows: given enough cathode potential, the reduction happened at the cathode/ionic liquids interface, where the oxygen was ionized, then dissolved in the ionic liquid and discharged at the anode, with the metallic Ti left at the cathode. [Copyright &y& Elsevier]