Synthesis of amorphous Mg(BH4)2 from MgB2 and H2 at room temperature

Abstract

Due to its high hydrogen content and its favourable overall thermodynamics magnesium tetrahydroborate has been considered interesting for hydrogen storage applications. In this work we show that unsolvated amorphous magnesium tetrahydroborate can be obtained by reactive ball milling of commercial MgB2 under 100 bar hydrogen atmosphere. The material was characterized by solid-state NMR which showed the characteristic features of Mg(BH4)2, together with those of higher borohydride species. High pressure DSC and TPD-MS showed thermal behaviour similar to that of Mg(BH4)2 but with broadened signals. In situ synchrotron X-ray powder diffraction confirmed the amorphous state of the material and showed the typical crystalline decomposition products of Mg(BH4)2 at elevated temperatures.