Insight to the Thermal Decomposition and Hydrogen Desorption Behaviors of NaNH 2 -NaBH 4 Hydrogen Storage Composite.

The lightweight compound material NaNH2 -NaBH4 is regarded as a promising hydrogen storage composite due to the high hydrogen density. Mechanical ball milling was employed to synthesize the composite NaNH2 -NaBH4 (2/1 molar ratio), and the samples were investigated utilizing thermogravimetric-differential thermal analysis-mass spectroscopy (TG-DTA-MS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) analyses. The full-spectrum test (range of the ratio of mass to charge: 0-200) shows that the released gaseous species contain H2 , NH3 , B2 H6 , and N2 in the heating process from room temperature to 400 °C, and possibly the impurity gas B6 H12 also exists. The TG/DTA analyses show that the composite NaNH2 -NaBH4 (2/1 molar ratio) is conductive to generate hydrogen so that the dehydrogenation process can be finished before 400 °C. Moreover, the thermal decomposition process from 200 to 400 °C involves two-step dehydrogenation reactions: (1) Na3 (NH2 )2 BH4 hydride decomposes into Na3 BN2 and H2 (200-350 °C); (2) remaining Na3 (NH2 )2 BH4 reacts with NaBH4 and Na3 BN2 , generating Na, BN, NH3 , N2 , and H2 (350-400 °C). The better mechanism understanding of the thermal decomposition pathway lays a foundation for tailoring the hydrogen storage performance of the composite complex hydrides system.