Hydrogen Storage Properties of Co-free La-Mg-Ni-Based Alloys

A series of Co-free La1.8Ti0.2MgNi9-xAlx (x=0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys were prepared by magnetic levitation melting under Ar atmosphere. The effects of partially substituting Al for Ni on the structure and hydrogen storage properties of the alloys were investigated. For the La1.8Ti0.2MgNi9-xAlx (x=0, 0.1, 0.2, 0.3, 0.4) alloys, LaMg2Ni9 phase is contained in all samples. when Al content x≥0.1, La(Ni, Al)5 phase replaces LaNi5 phase, LaNi3 phase disappears and LaNi2 phase appears. The enthalpies of the test alloys are close to −30.6 kJ/molH2 of the LaNi5 compound. Al substitution for Ni favors the improvement of discharge capacity, cycling stability and electrochemical kinetics. The optimum alloy is found to be La1.8Ti0.2MgNi8.7Al0.3 alloy, with the effective hydrogen storage capacity of 1.32 wt% (at 30 °C), the maximum discharge capacity of 340 mAh/g, the HRD1400 of 79.8% and the discharge capacity retention of 60% after 100 charging/discharging cycles.