Hydrogen in combination with a fuel cell is the most attractive option for a long-term sustainable energy development. Finding an efficient hydrogen storage material is one of the critical factors in realizing a hydrogen economy. Hydrazine borane (N2H4BH3, HB), with a 15.4 wt% of hydrogen content, has been viewed as a promising candicate for hydrogen storage. However, it decomposes to H2, N2H4 and (NHBH2)2 after pyrolysis. Hydrazinoboranes of various alkali metals, i.e., LiN2H3BH3, 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 hydrazinoboranes and their corresponding melting and dehydrogenation temperatures were observed. The dehydrogenation temperature was found dependent on the melting temperature. Upon approaching the melting points, alkali metal hydrazinoboranes dehydrogenate rapidly to release c.a 1 equiv. of H2 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 N2BH species. Compared to pristine N2H4BH3, the alkali-metal substituted hydrazinoboranes demonstrate significantly improved dehydrogenation behavior with no N2H4 emission and greatly suppressed NH3 release.

Alkali metal hydrazinoboranes for hydrogen storage

247th National Meeting (2014)

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