As a consequence of the combination of the formation and decomposition reactions of NaMg(NH(2)BH(3))(3), the 3NH(3)BH(3)/NaMgH(3) mixture can rapidly release ca. 10 wt.% of hydrogen at 80 °C within 2 min.
Ammonia borane (NH(3)BH(3), AB) is an intriguing molecular crystal with an extremely high hydrogen capacity and moderate thermal stability. In the present study, we show a simple but effective approach for destabilizing AB for promoted hydrogen release at moderate temperatures. It is found that mechanically milling with magnesium hydride (MgH(2)) can dramatically improve the dehydrogenation properties of AB, on both the kinetic and thermochemical aspects. For the mechanically milled AB/0.5MgH(2) material, over 8 wt% hydrogen can be released from AB within 4 h at around 100 degrees C without undesired volatile by-products. Moreover, the dehydrogenation reaction of the AB/0.5MgH(2) sample becomes significantly less exothermic than that of neat AB. In situ X-ray diffraction results demonstrate that the MgH(2) additive well maintains its phase stability during the ball-milling and the subsequent heating processes. Meanwhile, Raman spectroscopy and in situ(11)B NMR studies show that the MgH(2) additive exerts considerable influence on the chemical bonding state and decomposition process/products of AB. Combined phase/structure analyses results suggest that MgH(2) exerts effect via developing solid phase interaction with AB.
Lithium borohydride, LiBH 4 , possesses high hydrogen capacity, but cannot be used for hydrogen storage owing to the problematic H-exchange kinetics and thermodynamics. In the present study, we employed the Li + -Ca 2+ combination strategy to improve the de/rehydrogenation properties of LiBH 4 . Our study found that mechanically milling 1:1 LiBH 4 /Ca(BH 4 ) 2 mixture formed a dual-cation borohydride, Li 0.9 Ca(BH 4 ) 2.9 , which then transformed to stoichiometric LiCa(BH 4 ) 3 in the heating process. The formation and decomposition behaviors of LiCa(BH 4 ) 3 were studied using X-ray diffraction and thermogravimetry/differential scanning calorimetry/mass spectroscopy techniques. It was found that LiCa(BH 4 ) 3 differs significantly from the component phases in terms of physical properties, decomposition behaviors, and mechanistic pathway. In particular, LiCa(BH 4 ) 3 exhibits improved de/rehydrogenation properties relative to the component phases. These experimental findings exemplified the effectiveness of manipulation of dual-cation combination in tuning the de/rehydrogenation properties of the ionic light-metal borohydrides.
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