Direct synthesis and hydrogen storage characteristics of Mg–B–H compounds

This paper reports a comparative study of synthesizing Mg(BH4)2 by mechanically milling Mg + B, MgH2 + B and MgB2 powders following hydrogenation under hydrogen atmosphere. It has been shown that the milled Mg + B and MgH2 + B powders consisted of magnesium hydride and boron, while the milled MgB2 powder remained unchanged during the milling process. TEM, Raman spectra and TPD measurements confirmed the formation of amorphous Mg–B–H compounds in the milled Mg + B and MgH2 + B powders, which could be Mg(BxHy)n moieties. The total hydrogen desorption amounts after 3 h were 3.7 wt.% and 3.9 wt.% for the milled Mg + B and MgH2 + B powders respectively, whereas the milled MgB2 showed little apparent hydrogen desorption. After a hydrogenation process was carried out, the further hydrogenated MgB2 powder was found to contain the amorphous Mg–B–H compounds and could release 0.25 wt.% hydrogen.