Mechanically Milling with Off-the-Shelf Magnesium Powder to Promote Hydrogen Release from Ammonia Borane

Mechanically milling with the off-the-shelf magnesium (Mg) powder can dramatically improve the dehydrogenation properties of ammonia borane (AB) on all key aspects: enhancing the dehydrogenation kinetics, reducing the induction period, suppressing the formation of volatile byproduct, and alleviating the sample foaming. The postmilled AB/0.5Mg sample can release 8.2 wt % of hydrogen at 100 degrees C within 4 h and deliver >2.5 equiv of hydrogen in AB upon elevating the dehydrogenation temperature to 300 degrees C, giving a material-based hydrogen capacity of 12 wt To. Additionally, the dehydrogenation reaction of the AB/0.5Mg sample becomes significantly less exothermic than that of pristine AB, and remarkably, the third dehydrogenation step is tailored to be endothermic. Combination of phase/structure/chemical state analyses suggest that a considerable amount of Mg participates in the dehydrogenation process, resulting in the formation of Mg-N-B-H product(s).