Structural inhomogeneity: a potential strategy to improve the hydrogen storage performance of metal hydrides

Metal hydrides are prospective options for sustainable and clean energy carriers. Even though magnesium-based metal hydrides are considered potential hydrogen storage media, their sluggish dehydrogenation kinetics has limited their practical applications. In this study, Mg-Ni-based hydride with structural inhomogeneity was successfully prepared through a typical gas-solid reaction. The sample exhibited more remarkable hydrogen storage performance at relatively low temperatures compared to Mg₂NiH₄ prepared by the conventional method: it starts to release H₂ at ∼175 °C and completes under 250 °C with a saturated capacity of 3.55 wt%, and desorbs 3.09 wt% H₂ within 1200 s at 200 °C. As proved by density functional theory (DFT) calculations, MgNi₂ formed in situ during hydriding chemical vapor deposition can accelerate hydrogen release via the interfacial effect of Mg₂NiH₄/MgNi₂. Moreover, the nano-micro Mg-Ni-based hydride exhibited excellent stability in the cyclic test without kinetic decay and capacity loss, which can be attributed to the high reactivity of the surface layer. The results provide alternative insights into the energy storage properties of metal hydrides with structural inhomogeneity and a new vision for the design and synthesis of practical energy storage materials.