Synthesis and hydrogen storage thermodynamics and kinetics of Mg(AlH4)2 submicron rods

Mg(AlH4)2 submicron rods with 96.1% purity have been successfully synthesized in a modified mechanochemical reaction process followed by Soxhlet extraction. ∼9.0 wt% of hydrogen is released from the as-prepared Mg(AlH4)2 at 125–440 °C through a stepwise reaction. Upon dehydriding, Mg(AlH4)2 decomposes first to generate MgH2 and Al. Subsequently, the newly produced MgH2 reacts with Al to form a Al0.9Mg0.1 solid solution. Finally, further reaction between the Al0.9Mg0.1 solid solution and the remaining MgH2 gives rise to the formation of Al3Mg2. The first step dehydrogenation is a diffusion-controlled reaction with an apparent activation energy of ∼123.0 kJ/mol. Therefore, increasing the mobility of the species involved in Mg(AlH4)2 will be very helpful for improving its dehydrogenation kinetics.

► Mg(AlH4)2 submicron rods with high purity are successfully synthesized.
► ∼9.0 wt% of hydrogen is released from Mg(AlH4)2 with a three-step reaction.
► The resultant product is composed of Al3Mg2 and Al0.9Mg0.1.
► A diffusion-controlled kinetics is determined for the 1st step dehydrogenation.