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Ammine metal borohydrides (AMBs), with high hydrogen contents and favorable dehydrogenation properties, are receiving intensive research efforts for their potential as hydrogen storage materials. In this work, we report the successful synthesis of three ammine titanium borohydrides (denoted as ATBs), Ti(BH 4 ) 3 •5NH 3 , Li 2 Ti-(BH 4 ) 5 •5NH 3 , and Ti(BH 4 ) 3 •3NH 3 via metathesis reaction of metal chloride ammoniates (TiCl 3 •5NH 3 and TiCl 3 •3NH 3 ) and lithium borohydride. These ATBs present favorable stability, owing to the coordination with NH 3 groups, compared to the unstable Ti(BH 4 ) 3 at room temperature. Dehydrogenation results revealed that Ti(BH 4 ) 3 •5NH 3 , which theoretically contains 15.1 wt % hydrogen, is able to release ∼13.4 wt % H 2 plus a small amount of ammonia. This occurred via a single-stage decomposition process with a dehydrogenation peak at 130 °C upon heating to 200 °C. For Li 2 Ti(BH 4 ) 5 •5NH 3 , a three-step decomposition process with a total of 15.8 wt % pure hydrogen evolution peaked at 105, 120, and 215 °C was observed until 300 °C. In the case of Ti(BH 4 ) 3 •3NH 3 , a release of 14 wt % pure hydrogen via a two-step decomposition process with peaks at 109 and 152 °C can be achieved in the temperature range of 60−300 °C. Isothermal TPD results showed that over 9 wt % pure hydrogen was liberated from Ti(BH 4 ) 3 •3NH 3 and Li 2 Ti(BH 4 ) 5 •5NH 3 within 400 min at 100 °C. Preliminary research on the reversibility of this process showed that dehydrogenated ATBs could be partly recharged by reacting with N 2 H 4 in liquid ammonia. These aforementioned preeminent dehydrogenation performances make ATBs very promising candidates as solid hydrogen storage materials. Finally, analysis of the decomposition mechanism demonstrated that the hydrogen emission from ATBs is based on the combination reaction of B−H and N−H groups as in other reported AMBs.

The synthesis, crystal structure and dehydrogenation performances of two new H-enriched compounds, Mg(BH4)2(NH3BH3)2 and Mg(BH4)2·(NH3)2(NH3BH3), are reported. Due to the introduction of ammonia ligands, the Mg(BH4)2·(NH3)2(NH3BH3) exhibits dramatically improved dehydrogenation properties over its parent compound.

The structural stability and hydrogen adsorption capacity of an alkali (Li, Na and K) and alkali earth (Mg and Ca) metal atom decorated covalent triazine-based framework (CTF-1) are studied using ab initio density functional calculations. The calculation results revealed that Li, Na, K and Ca atoms can be adsorbed on the CTF-1 with the formation of a uniform and stable coverage due to the charge transfer between the metal atoms and the CTF-1 substrate, thus avoiding the clustering problem that occurs for the decoration of metal atoms on other substrates. The metal decorated CTF-1 could adsorb up to 30 hydrogen molecules with an average binding energy of $0.16-0.26 eV/H 2 , corresponding to a gravimetric density of 12.3, 10.3 and 8.8 wt% for the CTF-Li 6 , CTF-Na 6 and CTF-Ca 6 complexes, respectively, thereby enabling the Li, Na and Ca decorated covalent triazine-based frameworks to be very promising materials for effective reversible hydrogen storage at near ambient conditions. † Electronic supplementary information (ESI) available: Details of the optimized atomic structure, density of states (DOS), binding energies and Bader charges, including Fig. S1-S5 and Tables S1 and S2. See

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