Boosting the hydrogen storage performance of Mg-rich quaternary alloy hydrides via in-situ evolution of bidirectional catalytic phases

Abstract

Although Mg alloy-based hydrides have been considered as promising solid-state materials due to their high capacity and low cost, the high dehydrogenation temperature of ∼ 300℃ severely limited their practical application. Herein, a series of Mg-based quaternary alloys of Mg₈₅Ni₅Cu₅M₅ (M = Al, Zn, Co, La) hydrides were prepared by a combination of meltspinning and ball milling process, demonstrating an efficient approach to promoting the hydrogen storage properties. Among them, the Mg₈₅Ni₅Cu₅La₅ hydride (H-Mg₈₅Ni₅Cu₅La₅) as the most excellent one starts to release hydrogen from 175℃, 125℃ lower than that of MgH₂. Especially, the peak hydrogen release temperature of H-Mg₈₅Ni₅Cu₅La₅ was remarkedly reduced from 347℃ to 253℃, compared with MgH₂. Additionally, the H-Mg₈₅Ni₅Cu₅La₅ presented an impressive initial hydrogen capacity of 4.2 wt% with a high-capacity retention of 92.6 % over 10 dehydrogenation cycles. In/Ex-situ XRD analyses proved that the synergistic effects of in-situ formed metallic Ni and LaH₂ catalytic phases during the milling and ab/desorption processes can simultaneously enhance the ab/desorption kinetics of Mg/MgH₂. That is, the LaH₂ can act as a hydrogen pump to promote the dehydrogenation of hydrides, while the Ni is beneficial to accelerate the dissociation of metal-hydrogen atoms and the formation of hydrogen molecules on the surface of Mg alloy. These findings highlight the potential of multicomponent Mg-based alloys for practical use in solid-state hydrogen storage systems through in-situ formed catalytic phases.