Annealing effect on hydrogen storage property of Co-free La1.8Ti0.2MgNi8.7Al0.3 alloy

•As-cast and annealed La1.8Ti0.2MgNi8.7Al0.3 alloys are prepared.•The enthalpies of the alloys are close to −30.6 kJ/mol H2 of LaNi5 compound.•Annealed alloys exhibit higher hydrogen capacity and lower plateau pressure.•The cycle life and high rate dischargeability are improved markedly by annealing.•The appropriate annealing temperature for the alloy studied is 900 °C.

A series of Co-free La1.8Ti0.2MgNi8.7Al0.3 alloys are prepared by magnetic levitation melting followed by annealing treatment. The hydrogen storage properties of as-cast and annealed La1.8Ti0.2MgNi8.7Al0.3 alloys are investigated systematically. The results show that La(Ni,Al)5 and LaMg2Ni9 are the main phases and a LaNi2 phase disappears at 900 °C. The enthalpies of the experimental alloys are close to −30.6 kJ/mol H2 of LaNi5 compound. Comparing with as-cast alloy, annealed alloys exhibit larger hydrogen storage capacity, lower hydrogen absorption/desorption plateau pressure and longer cycle life. At 60% discharge capacity retention, the maximum charge–discharge cycles, 205 cycles (annealed 900 °C), are two times the minimum, 102 cycles (as-cast). The positive impact of annealing on the charge transfer rate at surface and the hydrogen diffusion rate in bulk enhances the high rate dischargeability. Annealed alloy (900 °C) shows good overall hydrogen storage properties.

Graphical abstractDischarge cycling performance of as-cast and annealed La1.8Ti0.2MgNi8.7Al0.3 alloy electrodes.Figure optionsDownload full-size imageDownload as PowerPoint slide