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

This paper reports a comparative study of synthesizing Mg(BH 4) 2 by mechanically milling Mg + B, MgH 2 + B and MgB 2 powders following hydrogenation under hydrogen atmosphere. It has been shown that the milled Mg + B and MgH 2 + B powders consisted of magnesium hydride and boron, while the milled MgB 2 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 MgH 2 + B powders, which could be Mg(B x H y ) n moieties. The total hydrogen desorption amounts after 3 h were 3.7 wt.% and 3.9 wt.% for the milled Mg + B and MgH 2 + B powders respectively, whereas the milled MgB 2 showed little apparent hydrogen desorption. After a hydrogenation process was carried out, the further hydrogenated MgB 2 powder was found to contain the amorphous Mg–B–H compounds and could release 0.25 wt.% hydrogen. ► We compared the synthesis pathways of Mg(BH 4) 2 by mechanically milling Mg + B, MgH 2 + B and MgB 2 powders following hydrogenation processes. ► The formation of amorphous Mg–B–H compounds in the milled Mg + B and MgH 2 + B powders was confirmed, which could be Mg(B x H y ) n moieties. ► The hydrogenated MgB 2 powder contained the amorphous Mg–B–H compounds and could release 0.25 wt. % hydrogen after further hydrogen process.