Mechanistic insight into the promoting effect of magnesium nickel hydride on the dehydrogenation of ammonia borane

In this paper, we report an in-depth study of the post-milled 4AB/Mg 2 NiH 4 sample, with a special focus on the promoting mechanism of Mg 2 NiH 4 on the dehydrogenation of AB. A combination of X-ray diffraction (XRD), Fourier transformation infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) characterizations, together with selective isotopic labelling and other designed experiments, revealed that AB and Mg 2 NiH 4 react with each other from the starting phase of the dehydrogenation process, which eventually results in the formation of Mg Ni B N H complexes. On the other hand, it was found that the reaction between AB and Mg 2 NiH 4 cannot proceed directly, but requires phase transition of normal AB to its mobile phase AB* to occur first. Hence, the promoting mechanism of Mg 2 NiH 4 on the dehydrogenation of AB is attributed to its promoting effect on phase transition of normal AB to AB* under mild conditions and in particular its chemical modification of AB with Mg and Ni.