Preparation and characterization of nanocrystalline Mg2FeH6

We report on the preparation and characterization of nanocrystalline Mg2FeH6 that is prepared by ball milling of 3Mg + Fe mixture under relatively lower hydrogen pressure (5.5 bar) at room temperature. The phase, composition and morphology of the as-milled powders are characterized by X-ray diffraction (XRD), Transmission electron microscope (TEM) and high-resolution TEM (HRTEM). The results show that the optimum formation time of Mg2FeH6 phase is 100 h and the abundance is about 90.1 wt% deduced from Reitveld refinement. Together with Mg2FeH6, small amount of Fe and MgO are also present in the milled product. The as-prepared nanocrystalline Mg2FeH6, which exhibits a chrysanthemum-like spherical shape (Ø 100–200 nm) with aggregated nanoparticles (Ø 10–20 nm), starts to desorb hydrogen at 335 K and ends at 613 K with a total weight loss of 5.15 wt%. The desorption enthalpy and entropy for the as-prepared nanocrystalline Mg2FeH6 are −67.2 ± 8 kJ/mol H2 and −120.1 ± 15 J/K mol H2, respectively.

Research highlights▶ High proportion of nanocrystalline Mg2FeH6 (with the diameter of about 10 nm) was prepared by ball milling technique under relatively lower hydrogen pressure and room temperature. ▶ Furthermore, the as-prepared sample desorbs up to 5.15 wt% of hydrogen under vacuum from 335 to 613 K.