Investigation on the structure and electrochemical properties of the rare-earth Mg-based hydrogen storage electrode alloys

XRD Rietveld analyses show that La0.7Mg0.3 (Ni0.85Co0.15)(x) (x = 2.5, 3.0, 3.5, 4.0, 4.5, 5.0) alloys are consisted of (La, Mg)Ni-3 phase and LaNi5 phase, and the (La, Mg)Ni3 phase content increases from 48.4% (x = 2.5) to 78.2% (x = 3.5) and then decreases to 12.2% (x = 5.0). The LaNi5 phase content maintains unchanged (about 20%) with increasing x from 2.5 to 3.5, and then increases to 71.9% with increasing x up to 4.0. The hydrogen storage capacity increases first and then decreases with increasing x, and the plateau becomes flatter and the plateau pressure first maintains almost unchanged and then increases with increasing x from 2.5 to 5.0. The electrochemical results show that the maximum discharge capacities of the alloy electrodes increase from 228.3 mA.h/g (x = 2.5) to 395.6 mA.h/g (x = 3.5), and then decrease to 226.8 mA.h/g (x = 5.0). Meanwhile, the high rate dischargeability (HRD) increases first and then decreases with increasing x from 2.5 to 4.5. Moreover, the electrochemical reaction kinetic of the alloy electrodes increases first to a maximum and then decreases with increasing x.