Tunable microstructure, de-/hydrogenation kinetics and thermodynamics performance of Mg–Ni–La–Ti–H systems

Abstract

In the light of positive effects of rare earth and transition metals on the hydrogen absorption/desorption properties of magnesium, the Mg20La–5TiH2, Mg20Ni–5TiH2 and Mg10Ni10La–5TiH2 composites have been prepared in this work to ameliorate the de-/hydrogenation kinetics and thermodynamic performance. The results indicate that the as-prepared composites are mainly composed of Mg, Mg2Ni/LaH3 and TiH2 phases after activation, and LaH3 and TiH2 are stable during de-/hydrogenation cycles. The morphology observations give evidences that LaH3 with size about ~20 nm and Mg2Ni with size about ~1 μm are uniformly distributed in the composites. It is noted that the de-/hydriding kinetics of the as-prepared composites are significantly improved after internal and surface modification, of which the Mg10Ni10La–5TiH2 composite can desorb as high as 5.66 wt% hydrogen within 3 min at 623 K. Moreover, the thermodynamic properties of the experimental composites have also been investigated and discussed according to the pressure-composition isothermal curves and corresponding calculation by Van't Hoff equation. The improved hydrogen storage properties of the as-prepared composites are mainly attributed to the uniformly distributed LaH3, Mg2Ni and TiH2 phases, which provide a large amount of phase boundaries, diffusion paths and nucleation sites for de-/hydrogenation reactions.