Magnesium borohydride Mg(BH4)2 for energy applications:A review

Mg(BH4)2 with several polymorphs,known as a high capacity(14.9 wt.％)hydrogen storage material,has become more intriguing due to the recently found new functions of gas physisorption and ionic conduc-tivity.Here we review the state-of-the-art on the energy related functions of Mg(BH4)2.Mg(BH4)2 tends to form the stable intermediate[B12H12]2-when the dehydrogenation temperature is above 400 ℃,the strong B-B bonding of which makes the rehydrogenation condition very harsh.In contrast,lower borane intermediate[B3H8]2-facilitates the rehydrogenation even at a mild condition of 100 ℃,suggesting the possibility of reversible hydrogen storage in Mg(BH4)2.The porous polymorph y-Mg(BH4)2 shows attrac-tive gas adsorption properties in view of its unique hydridic surface and pore shape,and potentially can be applied in hydrogen adsorption and Kr/Xe selectivity.A new diffraction-based adsorption methodology was developed to characterize adsorption thermodynamics and kinetics of γ-Mg(BH4)2,providing a novel idea for the characterization of crystalline porous materials.Moreover,the potential of Mg(BH4)2 as an electrolyte is discussed in the last part.Mg(BH4)2·THF/DME acts as a liquid electrolyte in Mg-batteries,while anion substituted or neutral molecule derivatives of Mg(BH4)2 can act as solid-state electrolyte.