Influence of annealing treatment on the hydrogen storage properties of La 2− xTi xMgNi 9 ( x = 0.2, 0.3) alloys

Abstract

La 2− x Ti x MgNi 9 ( x = 0.2, 0.3) alloys have been prepared by magnetic levitation melting under an Argon atmosphere, and the as-cast alloys were annealed at 800 °C, 900 °C for 10 h under vacuum. The effects of annealing on the hydrogen storage properties of the alloys were investigated systematically by XRD, PCT and electrochemical measurements. For the La 2− x Ti x MgNi 9 ( x = 0.2, 0.3) alloys, LaNi 5, LaMg 2Ni 9 and LaNi 3 are the main phases and a Ti 2Ni phase appears at 900 °C. The effective hydrogen storage capacity increases from 1.10, 1.10 wt.% (as-cast) to 1.22, 1.16 wt.% (annealed 800 °C) and 1.31, 1.27 wt.% (annealed 900 °C), respectively. The annealing not only improves the hydrogen absorption/desorption kinetics but also increases the maximum discharge capacity and enhances the cycling stability. The La 1.8Ti 0.2MgNi 9 alloy annealed at 900 °C exhibits good electrochemical properties, and the discharge capacities decrease from 366.1 mA h/g to 219.6 mA h/g after 177 charge-discharge cycles.