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

Abstract

Promotion of dehydrogenation based on the interaction of [BH4]− and [NH2]− sources has been demonstrated to be one of the most effective approaches in developing an advanced borohydride/amide hydrogen storage combined system. The Ca(BH4)2–2Mg(NH2)2 and Ca(BH4)2–2Ca(NH2)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(BH4)2. The hydrogen release measurements for Ca(BH4)2–2Mg(NH2)2 and Ca(BH4)2–2Ca(NH2)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(BH4)2 + 2 Mg(NH2)2 → 1/3 [Ca3Mg6(BN2)6] + 8 H2 and Ca(BH4)2 + 2 Ca(NH2)2 → 1/3 Ca9(BN2)6 + 8 H2, respectively. Compared with pristine Ca(BH4)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.