Study On Electrodeposition Of Ni-La Alloy In Ionic Liquids

Lanthanum and its alloys films have unique features due to the Lanthanum element has a unique electronic structure of 4f layer. For example, Ni-La alloy having great corrosion resistance, and when the composition of Ni-La reaches LaNis, it is a typical hydrogen storage alloy. LaNis has higher hydrogen-absorbing capacity, good cycle hydrogen absorption, desorption performance and without pollution etc. In this paper, the EMIC-EG ionic liquid is used as the electrolyte for the electrodeposition of Ni and Ni-La alloy. The mechanism of electrodeposition of Ni and Ni-La alloy has been investigated systematically by cyclic voltammetry, chronamperometry measurements, etc. The composition and morphology of the coatings were analysed by XRF, XRD, SEM, XPS ect.Electrochemical analysis shows that the process of Ni deposition is mainly controlled by diffusion in the EMIC-EG-NiCl2 electrolyte. The diffusion coefficient is 4.6x10-7 cm2/s and the diffusion activation energy is 21.75 kJ/mol. The increase of temperature and concentration are conducive to the reduction of Ni. When useing glassy carbon electrode or platinum electrode as working electrode, the deposition of Ni follows the three-dimensional instantaneous nucleation/growth process which controlled by diffusion.Electrochemical analysis shows that the oxidation-reduction reaction of La occurs in the EMIC-EG-NiCl2-LaCl3 electrolyte and the electrodeposition of Ni-La compliance the mechanism of induce codeposition. The codeposition of Ni-La occurs at a potential more positive when the temperature becomes higher. But when increasing the concentration of LaCl3, the codeposition of Ni-La occurs at a potential more negative. The codeposition of Ni-La at glassy carbon electrode follows the three-dimensional instantaneous nucleation/growth process which controlled by diffusion.When the current density is 1 mA/cm2, stainless steel as the cathode, smooth and slight brightness layer can be deposited in the EMIC-EG electrolyte which containing 0.1 mol/L Ni (II). And the layer is dense which the grains diameter is less than 100 nm. Ni-La alloy can be electrodeposited when copper as the cathode, graphite as the anode, in the EMIC-EG-NiCl2-LaCl3 electrolyte. The content of La increases in the alloy when the temperature and current density increase. But the content of La decreases in the alloy with the increases of the La (III) concentration. When the temperature is 373 K, the concentration of Ni (II) is 0.1 mol/L, the concentration of La (III) is 0.2 mol/L, current density is 5 mA/cm2, the highest content of La (7.3 at%) can be obtained. Isomorphous substitution appears in the Ni-La alloy, the large radius of La atoms substituted the small radius of Ni atoms. The alloy lattice constant is larger than the Ni. SEM micrographs show that increase the temperature and current density, the size of particles becomes large, and the alloy surface becomes rough. The surface morphology of Ni-La alloy from spherical clusters into dendritic structure when the concentration of La (III) increases.Corrosion resistance experiments prove that with the increase of the La content in the Ni-La alloy, the corrosion resistance of the alloy shows a trend that becomes good and then bad. The corrosion resistance of Ni-La alloy is best when the content of La is about 1.00 at.%.