Hydrogen storage properties of destabilized MgH2–Li3AlH6 system

To improve the dehydrogenation properties of MgH2, a novel hydrogen storage system, MgH2–Li3AlH6, is prepared by mechanochemical milling. Three physical mixtures containing different mole ratios (1:4, 1:1 and 4:1) of MgH2 and Li3AlH6 are studied and there exists a mutual destabilization effect between the components. The last mixture shows a capacity of 6.5 wt% H2 with the lowest starting temperature of dehydrogenation (170 °C). First, Li3AlH6 decomposes into Al, LiH and H2, and then the as-formed Al can easily destabilize MgH2 to form the intermetallic compound Mg17Al12 at a temperature of 235 °C, which is about 180 °C lower than the decomposition temperature of pristine MgH2. Finally, the residual MgH2 undergoes a self-decomposition whose apparent activation energy has been reduced by about 22 kJ mol−1 compared with pristine MgH2. At a constant temperature of 250 °C, the mixture can dehydrogenate completely under an initial vacuum and rehydrogenate to form MgH2 under 2 MPa H2, showing good cycle stability after the first cycle with a capacity of 4.5 wt% H2. The comparison between 4 MgH2 + Li3AlH6 and 4 MgH2 + LiAlH4 mixtures is also investigated.