Heterostructures Built in Metal Hydrides for Advanced Hydrogen Storage Reversibility

Abstract Hydrogen storage is a vital technology for developing on‐board hydrogen fuel cells. While Mg(BH₄)₂ is widely regarded as a promising hydrogen storage material owing to its extremely high gravimetric and volumetric capacity, its poor reversibility poses a major bottleneck inhibiting its practical applications. Herein, a facile strategy to effectively improve the reversible hydrogen storage performance of Mg(BH₄)₂ via building heterostructures uniformly inside MgH₂ nanoparticles is reported. The in situ reaction between MgH₂ nanoparticles and B₂H₆ not only forms homogeneous heterostructures with controllable particle size but also simultaneously decreases the particle size of the MgH₂ nanoparticles inside, which effectively reduces the kinetic barrier that inhibits the reversible hydrogen storage in both Mg(BH₄)₂ and MgH₂. More importantly, density functional theory coupled with ab initio molecular dynamics calculations clearly demonstrates that MgH₂ in this heterostructure can act as a hydrogen pump, which drastically changes the enthalpy for the initial formation of BH bonds by breaking stable BB bonds from endothermic to exothermic and hence thermodynamically improves the reversibility of Mg(BH₄)₂. It is believed that building heterostructures provides a window of opportunity for discovering high‐performance hydrogen storage materials for on‐board applications.