Synthesis, structures and dehydrogenation of magnesium borohydride-ethylenediamine composites

Magnesium borohydride−ethylenediamine composites (Mg(BH4)2−nEDA, n = 2, 3, 4), a new type of hydrogen storage material, were synthesized by ball milling magnesium borohydride and ethylenediamine (EDA). In particular, Mg(BH4)2∙3EDA and Mg(BH4)2∙4EDA can be well defined by a orthorhombic Pbca cell and a triclinic P1 cell, respectively. Hydrogen releasing from the Mg(BH4)2−nEDA composites was observed at elevated temperatures. Detailed dehydrogenation properties and mechanism of Mg(BH4)2-2EDA composite in which there are equivalent Hδ+(N) and Hδ−(B) were systematically investigated. Ca. 8 wt% hydrogen can be evolved from Mg(BH4)2-2EDA in one step upon holding it at 260 °C for 12 h. Mechanistic studies using phased dehydrogenation and isotopic labelling experiments show that hydrogen was released via the establishment of -NBN- bond as well as the combination of Hδ+ (N) and Hδ− (B).