The synthesis, structure and dehydrogenation of calcium borohydride hydrazinates

Calcium borohydride hydrazinates, Ca(BH4)2-nN2H4 (n = 4/3, 1, 2, 3) have been synthesized successfully. In particular, Ca(BH4)2
- 2N2H4 crystallizes in a monoclinic space group of C2/m with the lattice parameters of a = 10.1385 Å, b = 8.6342 Å, c = 4.6384 Å, β = 106.467°. It can release 5.9 equiv. gas/Ca(BH4)2 (approximately 8.8 wt. % H2) at 240 °C. Ca(BH4)2-N2H4 and Ca(BH4)2-4/3N2H4, on the other hand, show superior dehydrogenation properties under the same condition, i.e., around 9.2 wt.% and 10.8 wt.% hydrogen can be released from these two samples, respectively. It is suggested that two dehydrogenation pathways, i.e., direct combination of Hδ−-Hδ+ and ammonia-intermediated mechanisms, are likely to be involved in the process of dehydrogenation. Furthermore, the dehydrogenation temperature can be reduced significantly from 240 °C to 140 °C by introducing a Fe-based catalyst.