An improved hydrogen storage performance of MgH2 enabled by core-shell structure Ni/Fe3O4@MIL

Abstract

Magnesium hydride (MgH2) with high gravimetric hydrogen storage capacity is considered as one of the most potential hydrogen storage materials; however, its development has been plagued by the high operating temperature and slow kinetics. In this study, we have design and synthesize a core-shell Ni/Fe3O4@MIL additive to aid the (de)hydrogenation of MgH2/Mg system via the co-catalytic effect of in-situ formed Mg2NiH4/Mg2Ni and Fe. The initial dehydrogenation temperature significantly reduces from 613 K to 517 K, and the MgH2-Ni/Fe3O4@MIL composite can reabsorb 4.17 wt% H2 within 3600 s under 3.0 MPa H2 at 373 K. Remarkably, the dehydrogenation activation energy of the composite decreases by 61.77 kJ/mol compared to the pure MgH2 (159.71 kJ/mol). Moreover, the composite also shows good cycling stability without distinct capacity decay after cycling twenty times. Studies show that during dehydrogenation and hydrogenation processes, the Mg2NiH4/Mg2Ni act as catalysts to induce hydrogen desorption/absorption of MgH2/Mg. Meanwhile, the unique core-shell structure of the Ni/Fe3O4@MIL not only provides reaction sites, but also prevents the agglomeration of nanoparticles and maintains stable catalytic activity. This study provides a new idea for designing stable transition metal heterogeneous catalytic system to improve hydrogen storage performance of MgH2.