Promoted hydrogen release from ammonia borane by mechanically milling with magnesium hydride: a new destabilizing approach

Ammonia borane (NH3BH3, 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 (MgH2) can dramatically improve the dehydrogenation properties of AB, on both the kinetic and thermochemical aspects. For the mechanically milled AB/0.5MgH2 material, over 8 wt% hydrogen can be released from AB within 4 h at around 100 °C without undesired volatile by-products. Moreover, the dehydrogenation reaction of the AB/0.5MgH2 sample becomes significantly less exothermic than that of neat AB. In situ X-ray diffraction results demonstrate that the MgH2 additive well maintains its phase stability during the ball-milling and the subsequent heating processes. Meanwhile, Raman spectroscopy and in situ11B NMR studies show that the MgH2 additive exerts considerable influence on the chemical bonding state and decomposition process/products of AB. Combined phase/structure analyses results suggest that MgH2 exerts effect via developing solid phase interaction with AB.