Mechanical alloying and electronic simulations of 2Mg–Fe mixture powders for hydrogen storage

2Mg–Fe powder mixture was milled in hydrogen atmosphere to prepare materials for hydrogen storage. The microstructure and dehydrogenating property of the milled system were examined. Then energy and electronic structure of the hydride phase were investigated by using a first-principles plane-wave pseudopotential method to explain the experimental results from XRD, DSC and TGA analysis. By calculating the heats of formation of MgH2, (MgFe)H2 solid solutions and Mg2FeH6 compound, the forming process of Mg2FeH6 was assumed as that magnesium was first dissolved in some H atoms to form MgH2, second, iron atom progressively dissolved into MgH2 lattice to form (MgFe)H2 solid solutions, finally the (MgFe)H2 solid solution can be changed into Mg2FeH6 phase. For DSC curves as a function of temperature for all the powders milled for different time, a drastic change of dissociation temperature is never found, this kind of relatively sluggish change can be explained using the idea on forming process of Mg2FeH6. Since MgH2 phase is still the major phase in the coexistence mixtures of two types of hydrides β-MgH2 and Mg2FeH6, Mg2FeH6 reduces the negative formation heat of the mixture compared with that of MgH2, which indicates that Mg2FeH6 lowers the desorption temperature of MgH2 through a catalytic effect and the milled powder containing duplex β-MgH2 + Mg2FeH6 exhibits the most rapid desorption rate among all the powders studied from TGA analysis.