Renewed Insight into the Promoting Mechanism of Magnesium Hydride on Ammonia Borane

Our previous study found that mechanically milling with magnesium hydride (MgH 2 ) could dramatically improve the dehydrogenation property of ammonia borane (AB). Meanwhile, it appears that the MgH 2 additive maintains its phase stability in the milling and subsequent heating process. In an effort to further the mechanistic understanding of the AB/MgH 2 system, we reinvestigated the property and structure evolution in the hydrogen release process of the AB/0.5MgH 2 sample. Property examination using volumetric method and synchronous thermal analyses showed that the AB/0.5 MgH 2 sample releases ∼13.8 wt % hydrogen after being heated at 300 °C. This hydrogen amount is in excess of that available from AB, indicative of the participation of a faction of MgH 2 in the dehydrogenation process of AB. Structural and chemical state analyses using Fourier transformation infrared spectroscopy and solid‐state 11 B nuclear magnetic resonance techniques further showed that part of MgH 2 participates in the dehydrogenation process of AB from the first step, resulting in the formation of MgBNH intermediate species. The incorporation of Mg in AB is believed to be a crucial event leading to dehydrogenation property improvements, particularly for the release of the last equivalent of H 2 in AB at relatively moderate temperature. These findings have provided renewed insight into the promoting mechanism of MgH 2 on the hydrogen release from AB.