Improved Dehydrogenation Properties of Calcium Borohydride Combined with Alkaline-Earth Metal Amides

Promotion of dehydrogenation based on the interaction of [BH 4 ] − and [NH 2 ] − sources has been demonstrated to be one of the most effective approaches in developing an advanced borohydride/amide hydrogen storage combined system. The Ca(BH 4 ) 2 –2Mg(NH 2 ) 2 and Ca(BH 4 ) 2 –2Ca(NH 2 ) 2 composites are thereby synthesized in the present work. It is found that the binary combined systems exhibit an onset dehydrogenation temperature of ∼220 °C, which is ∼100 °C lower than that of pristine Ca(BH 4 ) 2 . The hydrogen release measurements for Ca(BH 4 ) 2 –2Mg(NH 2 ) 2 and Ca(BH 4 ) 2 –2Ca(NH 2 ) 2 samples below 480 °C show desorption amounts of 8.3 and 6.8 wt % hydrogen, respectively. The dehydrogenation of both samples is accompanied by an ammonia emission of <1.4 mol %. The characterizations such as X-ray diffraction and nuclear magnetic resonance on the postdehydrogenated samples indicate that the dehydrogenation reactions are in the pathways of Ca(BH 4 ) 2 + 2 Mg(NH 2 ) 2 → 1/3 [Ca 3 Mg 6 (BN 2 ) 6 ] + 8 H 2 and Ca(BH 4 ) 2 + 2 Ca(NH 2 ) 2 → 1/3 Ca 9 (BN 2 ) 6 + 8 H 2, respectively. Compared with pristine Ca(BH 4 ) 2 sample, both possess lower activation energy for dehydrogenation. Further investigation reveals that the interaction of B–H and N–H may be one of main driving forces for dehydrogenation of borohydride/amide combined system.