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.

Discharge cycling performance of as-cast and annealed La1.8Ti0.2MgNi8.7Al0.3 alloy electrodes.Figure optionsDownload as PowerPoint slide