Improved Hydrogen Storage Properties and Air Stability of Metal Hydrides by Constructing Heterophase Composites

Hydrogen stored in metal hydrides is a promising solution for sustainable and clean energy carriers. While Mg 2 NiH 4 is regarded as a potential hydrogen storage medium due to its relatively low dehydrogenation temperature, severe surface passivation has hindered its practical application. In this work, a series of heterophase Mg–Ni-based composites are synthesized via the hydriding combustion synthesis (HCS) method. The in situ-formed MgNi 2 can serve as highly reactive and air-stable sites for hydrogen dissociation, leading to superior dehydrogenation kinetic properties of the heterophase composites. The dehydrogenation activation energy is sharply decreased from 130.7 kJ/mol H 2 (pure Mg 2 NiH 4 ) to 59.5 kJ/mol H 2 (Mg 1.9 NiH x, containing only 3.1 wt % MgNi 2 ). Surface characterization and density functional theory calculations reveal that the lower surface segregation and oxidation of MgNi 2 compared to Mg 2 NiH 4 is responsible for improving the dehydrogenation performance. Moreover, the heterophase composites can be preserved, transferred, and operated under environmental conditions without specific treatment or strict atmosphere, which is an essential feature in practical applications. This work proposes a new approach to simultaneously improve the kinetic property and air stability of metal-based hydrogen storage materials, thereby promoting the commercialization of hydrogen energy.