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

摘要

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_xH_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.