Synthesis of the hydride mixtures (1 − x)AlH3/xMgH2 (0 ≤ x ≤ 0.3) by ball milling and their hydrogen storage properties

In an effort to thermodynamically stabilize the alane (i.e., to increase the desorption enthalpy), partial substitution of Mg for Al was investigated by ball milling the mixtures (1 − x)AlH3/xMgH2 (x = 0.1, 0.2 and 0.3). Rietveld analysis of the XRD profiles showed that the cell volume of α-AlH3 increased with the Mg substitution rate, and thereby formation of solid solutions was assumed (x ≤ 0.05). In agreement with the experimental results, theoretical calculations indicated that a hypothetical supercell structure (MgAl15)H47 (x = 0.0625), which contained a hydrogen vacancy, was at least metastable. However, the effect of alane stabilization by Mg substitution for Al was not observed, either by experiment or by simulation, and only an increase in the activation energy was measured.