Electrochemical Studies On BMIC - GL Ionic Liquid Electrodeposition Of Magnesium - Nickel Alloy

Owing to higher hydrogen-absorbing capacity, better cycle hydrogen absorption and desorption performance, lower environmental loading, without pollution etc., Mg-Ni hydrogen storage alloy is considered one of the most promising hydrogen storage material. Electrodeposition was a potential method for preparing Mg-Ni alloy due to easily operate, simple device, and controling the composition and structure of the alloy by adjusting electrodeposition parameters. The standard electrode potential of magnesium was more negative than nickle, so difficult to electrodeposit Mg-Ni alloy from aqueous solution.Room temperature ionic liquids with a series of advantage for wide electrochemical window, large liquid temperature range, without hydrogen evolution reaction, etc., could be as an excellent alternative solvent to electrodeposite Mg-Ni alloy. In this paper, the BMIC-GL (1-butyl-3-methylimidazolium chloride-glycerin) ionic liquids as solvents to electrodeposite Mg-Ni alloys due to simplely synthesized process and high conductivity. The contents were as follows:The ionic liquid BMIC-GL was synthesized, and the analysis of IR(infrared spectrum) showed that it was the target ionic liquid, and conductivity of solution may changed when changed the molar ratio of BMIC and GL,when the molar ratio of BMIC and GL was1/2, the conductivity of the system was largest.Potentiodynamic polarization curve were adopt to explore the dissolution process of a nickel electrode in ionic liquid BMIC-GL polarization curve. The results indicate that the anodic dissolution process of nickel can be divided into electrochemically-controlled, hybrid-controlled and diffusion-controlled regimes. The anodic limiting current density increased and the dissolution,of nickel accelerated with the agitation, increasing temperature and increasing concentration of Ni2+in the ionic liquid.Tafel curves were adopt to measure the equilibrium potential of Mg and Ni in ionic liquid BMIC-GL. The results indicate that the equilibrium potential of Ni/Ni2+would be noble with increasing the molar concentration of Ni2+, the equilibrium potential of Mg/Mg2+would negative shift with increasing the molar concentration of Mg2+. Results:when the molar ratio were (0.05～0.1mol·L-1), the different value about the equilibrium potential of Mg and Ni in ionic liquid was least, therefore,we chosed that molarity range to experiment; Increasing temperature could make the equilibrium potential of Mg and Ni positive shift, when the temperature was353K, the difference value of the balance potential was least and be good for Mg-Ni alloy codeposition.We explored the electrochemical properties of ionic liquid electrolyte by measuring the CV curve of BMIC-GL, BMIC-GL-NiCl2, BMIC-GL-NiCl2-MgCl2ionic liquids.The results showed that the addition of Mg2+in ionic liquid, the CV curve appeared the magnesium reduction peak, could realize the Mg-Ni alloy codeposition, but the ionic liquid resolved with electro-deposition. The dissolution process of nickel was diffusion-controlled, and the diffusion coefficient of Ni2+was7.633×10-7cm-2·s-1. We explored the effect of the concentration of Mg2+, the concentration of Ni2+and cell voltage on the deposit morphology and the concent of magnesium with the copper substrate. The results showed that the morphology of sedimentary sequences and the concent of magnesium were affected by the concentration of Mg2+, the concentration of Ni2+and the cell voltage.when the concentration of Mg2+, the concentration of Ni2+were0.1mol·L-1, the cell voltage was1.4V, the content of magnesium in Mg-Ni alloy reached to4.14%.