Precipitation of nanocrystalline LaH3 and Mg2Ni and its effect on de-/hydrogenation thermodynamics of Mg-rich alloys

Abstract

Based on the catalytic effects of transition metals and rare earth metals on magnesium hydride, precipitation behavior of nanocrystalline LaH3 and Mg2Ni has been discussed and correlated with the de-/hydrogenation thermodynamic of Mg-rich alloys in this work. The results show that a significant enhancement of de-/hydrogenation properties has been achieved due to in-situ formed Mg–Mg2Ni–LaH3 nanocomposites. It is observed that the Mg2Ni-rich alloy exhibiting superior performance can desorb about 5.7 wt% hydrogen within 2.5 min at 623 K. The formation of LaH3 tends to promote the hydrogenation process and the Mg2Ni is beneficial for improving the dehydrogenation performance. Meanwhile, the phase boundaries between LaH3, Mg2Ni and Mg also play positive roles due to stored extra energy on the interface. Fitting kinetics model shows that rate-limiting steps of the as-prepared alloys have changed and the desorption activation energy significantly decreases due to precipitation of nanocrystalline LaH3 and Mg2Ni. It is worth noting that desorption activation energy of the preferable composite decreases to 94.03 kJ mol−1. Thermodynamic properties are also investigated and analyzed based on plateau pressure and van't Hoff equation. It is revealed that precipitation of nanocrystalline LaH3 and Mg2Ni significantly enhances the hydrogen storage kinetics of Mg-based alloys.