Magnesium borohydride hydrolysis with kinetics controlled by ammoniate formation

The possibility of hydrogen generation by hydrolysis of magnesium borohydride and its ammoniates was explored. Results show that catalyst-free Mg(BH4)2 can generate 1700 mL (H2)·g−1 in 1 min, 2760 mL (H2)·g−1 in 2 h, and 3004 mL (H2)·g−1 in 5 h without any diborane (B2H6) emission. Mg(BH4)2 presents the highest hydrogen yield reported to date. However, the hydrogen generation rate of Mg(BH4)2 may be too fast to be controllable in some hydrogen production cases. Therefore, NH3 was added to form ammoniates to further regulate the hydrogen supply kinetics of Mg(BH4)2. The hydrogen yields of Mg(BH4)2·0.5NH3, Mg(BH4)2·NH3, Mg(BH4)2·2NH3, Mg(BH4)2·3NH3 and Mg(BH4)2·6NH3 are 2376, 2029, 1780, 1665 and 1180 mL (H2) g−1, respectively, which demonstrates a well-controlled hydrogen supply rate. These results indicate that catalyst-free Mg(BH4)2 and its ammoniates have good hydrolysis performance and show promise as convenient high-density hydrogen generation materials.