Electrochemical hydrogen storage properties of non-equilibrium Ti_2-xMg_xNi alloys

Amorphous Ti_2-xMg_xNi (x=0-0.3) alloys were prepared by mechanical milling of elemental powders. Charge and discharge test, linear polarization (LP) and potential-step measurement were carried out to investigate the electrochemical hydrogen storage properties of the alloys before and after heat treatment. The results show that the maximum discharge capacity of heat-treated Ti_2-xMg_xNi alloy can reach 275.3 mA·h/g, which is 100 mA·h/g higher than that of the amorphous Ti_2-xMg_xNi alloy. The heat-treated Ti_1.9Mg_0.1Ni alloy presents the best cycling stability with a high discharge capacity of 210 mA·h/g after 30 cycles. The results of LP and potential-step measurement of the Ti_1.9Mg_0.1Ni alloy show that the exchange current density increases from 101.1 to 203.3 mA/g and the hydrogen diffusion coefficient increases from 3.20×10^-11 to 2.70×10^-10 cm²/s after the heat treatment, indicating that the heat treatment facilitates both the charge-transfer and hydrogen diffusion processes, resulting in an improvement in electrochemical hydrogen storage properties of Ti_2-xMg_xNi (x=0-0.3) alloys.