Nanoparticulate ZrNi: In Situ Disproportionation Effectively Enhances Hydrogen Cycling of MgH2

High thermal stability and sluggish absorption/desorption kinetics are still important limitations for using magnesium hydride (MgH₂) as a solid-state hydrogen storage medium. One of the most effective solutions in improving hydrogen storage properties of MgH₂ is to introduce a suitable catalyst. Herein, a novel nanoparticulate ZrNi with 10-60 nm in size was successfully prepared by co-precipitation followed by a molten-salt reduction process. The 7 wt % nano-ZrNi-catalyzed MgH₂ composite desorbs 6.1 wt % hydrogen starting from ∼178 °C after activation, lowered by 99 °C relative to the pristine MgH₂ (∼277 °C). The dehydrided sample rapidly absorbs ∼5.5 wt % H₂ when operating at 150 °C for 8 min. The remarkably improved hydrogen storage properties are reasonably ascribed to the in situ formation of ZrH₂, ZrNi₂, and Mg₂NiH₄ caused by the disproportionation reaction of nano-ZrNi during the first de-/hydrogenation cycle. These catalytic active species are uniformly dispersed in the MgH₂ matrix, thus creating a multielement, multiphase, and multivalent environment, which not only largely favors the breaking and rebonding of H-H bonds and the transfer of electrons between H^- and Mg²⁺ but also provides multiple hydrogen diffusion channels. These findings are of particularly scientific importance for the design and preparation of highly active catalysts for hydrogen storage in light-metal hydrides.