Synergistic hydrogen desorption behavior of magnesium aluminum hydride synthesized by mechano-chemical activation method

A mechano-chemical activation synthesis (MCAS) is employed to fabricate Mg(AlH4)2 via milling the precursors, specifically NaAlH4 and MgCl2. The corresponding dehydrogenation behavior of the synthesized powders is investigated. The experimental results showed that incomplete synthesis or premature dehydrogenation may occur if the milling process was not properly controlled. The hydrogen content of each synthesized powder is determined by using a thermal gravimetric analyzer (TGA). The dehydrogenation reactions of the synthesized powders are investigated by employing ex situ X-ray diffraction (XRD), in situ synchrotron XRD and differential thermal analysis (DTA). The results showed that the incompletely synthesized powder consisted of residual NaAlH4 in the synthesized Mg(AlH4)2, which demonstrated an initial dehydrogenation temperature as low as 100 °C and accompanied with a maximum amount (3.1 wt%) of H2 released below 350 °C. The mutual catalytic effect of both NaAlH4 and Mg(AlH4)2 on lowering their initial dehydrogenation temperature is confirmed.

► Mg(AlH4)2 could release 3.1 wt% H2 at initial temperature as low as 100 °C.
► The synergistic and mutual catalytic effects of NaAlH4 and Mg(AlH4)2 were noticed.
► In situ synchrotron XRD confirmed the two-step dehydrogenation process of Mg(AlH4)2.