Synergetic Effects of In Situ Formed CaH 2 and LiBH 4 on Hydrogen Storage Properties of the Li–Mg–N–H System

Hydrogen storage properties and mechanisms of the Ca(BH 4 ) 2 ‐doped Mg(NH 2 ) 2 –2 LiH system are systematically investigated. It is found that a metathesis reaction between Ca(BH 4 ) 2 and LiH readily occurs to yield CaH 2 and LiBH 4 during ball milling. The Mg(NH 2 ) 2 –2 LiH–0.1 Ca(BH 4 ) 2 composite exhibits optimal hydrogen storage properties as it can reversibly store more than 4.5 wt % of H 2 with an onset temperature of about 90 °C for dehydrogenation and 60 °C for rehydrogenation. Isothermal measurements show that approximately 4.0 wt % of H 2 is rapidly desorbed from the Mg(NH 2 ) 2 –2 LiH–0.1 Ca(BH 4 ) 2 composite within 100 minutes at 140 °C, and rehydrogenation can be completed within 140 minutes at 105 °C and 100 bar H 2 . In comparison with the pristine sample, the apparent activation energy and the reaction enthalpy change for dehydrogenation of the Mg(NH 2 ) 2 –2 LiH–0.1 Ca(BH 4 ) 2 composite are decreased by about 16.5 % and 28.1 %, respectively, and thus are responsible for the lower operating temperature and the faster dehydrogenation/hydrogenation kinetics. The fact that the hydrogen storage performances of the Ca(BH 4 ) 2 ‐doped sample are superior to the individually CaH 2 ‐ or LiBH 4 ‐doped samples suggests that the in situ formed CaH 2 and LiBH 4 provide a synergetic effect on improving the hydrogen storage properties of the Mg(NH 2 ) 2 –2 LiH system.