Effect of partial substitution of Ti for Al on the phase structure and electrochemical hydrogen storage properties of Mg₃AlNi₂ alloy

Ti was introduced into Mg₃AlNi₂ to partly substitute Al to improve the electrochemical hydrogen storage properties. Several alloys, namely Mg₃Al_1-xTi_xNi₂ (x = 0, 0.2, 0.4, 0.6), were prepared by pretreatment of ultrasonic dispersion and high energy ball milling, followed by sintering. X-ray diffraction study indicates that all the alloys show multiphase structures. Galvanostatic charge and discharge experiments show that the maximun discharge capacity and the cycle stability of Mg₃AlNi₂ alloy electrode are significantly improved after partial substitution of Ti for Al. Field emission scanning electron microscopy was performed to directly observe the surface morphology evolution of the alloys before and after 50 charge-discharge cycles in electrolyte in order to investigate the anti-pulverization ability, while Tafel polarization was carried out to study the anti-corrosion ability. Our results show that the discharge capacity degradation of the Mg₃Al_1-xTi_xNi₂ (x = 0, 0.2, 0.4, 0.6) alloys is mainly attributed to the pulverization of alloy particles in electrolyte. The high rate discharge ability of the alloys can also be remarkably enhanced by proper substitution of Ti for Al. Potentiostatic discharge, linear polarization and electrochemical impedance spectra were carried out to further investigate the kinetic properties, and it was found that proper substitution of Ti for Al could greatly improve surface activity and hydrogen diffusion ability of the Mg₃AlNi₂ electrode alloy.