Mg/MgH2 hydrogen storage system destabilized by recyclable AlH3–NaBH4 composite

While borohydrides , such as NaBH 4 , were often used as supplements to improve hydrogen storage properties of Mg/MgH 2 systems, they have long suffered from high decomposition temperature and irreversible dehydrogenation process. Here, we report that NaBH 4 can reversibly serve as a hydrogen storage host and reactant for Mg/MgH 2 systems under mild reaction conditions with the help of Al/AlH 3 . 90 wt%MgH 2 –5 wt.%AlH 3 –5 wt.%NaBH 4 (M-5AB) has been successfully synthesized using the conventional mechanical alloying technique. The dehydrogenation activation energy and enthalpy are 20% and 9% reduced than those of pure Mg/MgH 2 . After 10 hydrogen absorption and desorption cycles, the hydrogen storage capacity of M-5AB can reach 6.35 wt%. The X-ray diffraction (XRD) and the transmission electron microscope (TEM) measurements revealed that the interface of additives and Mg/MgH 2 decompose to Mg 17 Al 12 , MgAlB 4 and NaH phases. The Mg 17 Al 12 and MgAlB 4 phases reduces the barrier of free energies of hydrogenated and dehydrogenated states, helping NaBH 4 to recover after rehydrogenation. These discoveries indicate that Al species can boost the decomposition and reformation of NaBH 4 , providing a wider degree of freedom for the material design of Mg-based hydrogen storage materials .