Multi-hydride systems with enhanced hydrogen storage properties derived from Mg(BH<inf>4</inf>)<inf>2</inf> and LiAlH<inf>4</inf>

Abstract

A two-step ball-milling method has been provided to synthesize Mg(BH4)2using NaBH4and MgCl2as starting materials. The method offers high yield and high purity (96%) of the compound. The as-synthesized Mg(BH4)2is then combined with LiAlH4by ball-milling in order to form new multi-hydride systems with high hydrogen storage properties. The structure, the dehydrogenation and the reversibility of the combined systems are studied. Analyses show that a metathesis reaction takes place between Mg(BH4)2and LiAlH4during milling, forming Mg(AlH4)2and LiBH4. Mg(BH4)2is excessive and remains in the ball-milled product when the molar ratio of Mg(BH4)2to LiAlH4is over 0.5. The onset dehydrogenation temperature of the combined systems is lowered to ca. 120 °C, which is much lower than that of either Mg(BH4)2or LiAlH4. The dehydrogenation capacities of the combined systems below 300 °C are all higher than that of both Mg(BH4)2and LiAlH4. The combined systems are reversible for hydrogen storage at moderate hydrogenation condition, and rapid hydrogenation occurred within the initial 30 min. Moreover, the remained Mg(BH4)2in the combined systems is found also partially reversible. The mechanism of the enhancement of the hydrogen storage properties and the dehydrogenation/ hydrogenation process of the combined systems were discussed. © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.