Study on the dehydrogenation properties and reversibility of Mg(BH4)2[sbnd]AlH3 composite under moderate conditions

Abstract

Mg(BH4)2 has been considered as one of the promising light metal complex hydrides due to its high hydrogen capacity and low cost. But its higher thermal stability (dehydrogenation at above 300 °C) needs to be improved for the practical application. In this study, the aluminum hydride AlH3 was introduced into complex borohydride Mg(BH4)2 to synthesize a new Mg(BH4)2AlH3 composite by ball milling method. It is found that the active Al∗ formed from the self-decomposition of AlH3 can effectively improve the dehydrogenation properties of Mg(BH4)2, the Mg(BH4)2AlH3 composite starts to release hydrogen at 130.8 °C with a total hydrogen capacity of 11.9 wt.%. The dehydrogenated products of the composite is composed of Mg2Al3 and B at 350 °C, resulting in the improved hydrogen desorption properties of Mg(BH4)2AlH3 composite. The Mg2Al3 and B products would be further transformed into MgAlB4 and Al at 500 °C. Moreover, the Mg2Al3 and B dehydrogenated products show better reversible hydrogen storage property than that of the MgAlB4 and Al products. This research shows a way to alter hydrogen de/hydrogenation route and reversibility of Mg(BH4)2 complex hydride by compositing with AlH3 and controlling the dehydrogenation temperature.