Improved hydrogen storage properties of Mg-based nanocomposite by addition of LaNi₅ nanoparticles

Mg (200 nm) and LaNi₅ (25 nm) nanoparticles were produced by the hydrogen plasma-metal reaction (HPMR) method, respectively. Mg-5 wt.% LaNi₅ nanocomposite was prepared by mixing these nanoparticles ultrasonically. During the hydrogenation/dehydrogenation cycle, Mg-LaNi₅ transformed into Mg-Mg₂Ni-LaH₃ nanocomposite. Mg particles broke into smaller particles of about 80 nm due to the formation of Mg₂Ni. The nanocomposite showed superior hydrogen sorption kinetics. It could absorb 3.5 wt.% H₂ in less than 5 min at 473 K, and the storage capacity was as high as 6.7 wt.% at 673 K. The nanocomposite could release 5.8 wt.% H₂ in less than 10 min at 623 K and 3.0 wt.% H₂ in 16 min at 573 K. The apparent activation energy for hydrogenation was calculated to be 26.3 kJ mol^-1. The high sorption kinetics was explained by the nanostructure, catalysis of Mg₂Ni and LaH₃ nanoparticles, and the size reduction effect of Mg₂Ni formation.