Structural and electrochemical characteristics of Mg(55−x)TixNi(45−y)Pty metal hydride electrodes

In recent years, Mg–Ni-based metastable alloys have been attracting attention due to their large hydrogen sorption capacities, low weight, low cost, and high availability. Despite the large discharge capacity and high activity of these alloys, the accelerated degradation of the discharge capacity after only few cycles of charge and discharge is the main shortcoming against their commercial use in batteries. The addition of alloying elements showed to be an effective way of improving the electrode performance of Mg–Ni-based alloys. In the present work, the effect of Ti and Pt alloying elements on the structure and electrode performance of a binary Mg–Ni alloy was investigated. The XRD and HRTEM revealed that all the investigated alloy compositions had multi-phase nanostructures, with crystallite size in the range of 6 nm. Moreover, the investigated alloying elements demonstrated remarkable improvements of both maximum discharge capacity and cycling life. Simultaneous addition of Ti and Pd demonstrated a synergetic effect on the electrochemical properties of the alloy electrodes. Among the investigated alloys, the best electrochemical performance was obtained for the Mg51Ti4Ni43Pt2 composition (in at.%), which achieved 448 mAh g−1 of maximum discharge capacity and retained almost 66% of this capacity after 10 cycles. In contrast, the binary Mg55Ni45 alloy achieved only 248 mAh g−1 and retained 11% of this capacity after 10 cycles.