Heterostructures Built in Metal Hydrides for Advanced Hydrogen Storage Reversibility.

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 B2 H6 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.