Alkali Metal Hydride Modification on Hydrazine Borane for Improved Dehydrogenation

Hydrazidotrihydridoborates of various
alkali metals, i.e., NaN2H3BH3 and
KN2H3BH3, were synthesized successfully
via a liquid approach.
The crystal structures of NaN2H3BH3 and KN2H3BH3 were determined, and
their dehydrogenation properties were compared with LiN2H3BH3 and N2H4BH3. A clear correlation between sizes of metal cations in hydrazidotrihydridoborates
and their corresponding melting and dehydrogenation temperatures was
observed. The dehydrogenation temperature was found dependent on the
melting temperature. Upon approaching the melting points, alkali metal
hydrazidotrihydridoborates dehydrogenate rapidly in the first step,
giving rise to the formation of intermediates that possess N2BH2, N2BH, and NBH3 species. Further
increasing temperature leads to the release of additional H2 and the formation of N2BH species. Compared to pristine
N2H4BH3, the alkali-metal-substituted
hydrazidotrihydridoborates demonstrate significantly improved dehydrogenation
behavior with no N2H4 emission and greatly suppressed
NH3 release.