Insight to the Thermal Decomposition and Hydrogen Desorption Behaviors of NaNH₂-NaBH₄ 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, B₂H₆, and N₂ in the heating process from room temperature to 400 °C, and possibly the impurity gas B₆H₁₂ 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)₂BH₄ hydride decomposes into Na₃BN₂ and H₂ (200-350 °C); (2) remaining Na₃(NH₂)₂BH₄ reacts with NaBH₄ and Na₃BN₂, 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.