Rerouting Pathways of Solid-State Ammonia Borane Energy Release

Ammonia borane (NH3BH3, AB) represents a promising energy-dense material for hydrogen storage and propulsion; however, its energy release mechanisms on oxidation by solid-state oxidizers are not well understood. In this study, through in situ time-of-flight mass spectrometry supported by attenuated total reflection-Fourier transform infrared spectroscopy and density functional theory calculations, we investigate the fundamental reaction mechanisms involved in the energy release from solid-state AB with different chemical oxidizers. We show that the reaction of AB with oxidizers like KClO4 is mediated by [NH3BH2NH3](+)[BH4](-) (DADB) formation, resulting in its kinetic entrapment into low-energy BNHx clusters that are resistant to further oxidation, thus limiting complete energy extraction. In contrast, with an ammonium-based oxidizer such as NH4ClO4, the presence of NH4+ ions enables AB to follow an alternative reaction pathway forming [NH3BH2NH3](+)[ClO4](-) rather than DADB, thus inhibiting the formation of BNHx species and facilitating its complete oxidation. This alternative reaction route causes the AB/NH4ClO4 system to exhibit remarkably higher energy release rates over that of AB/KClO4 (similar to 27x) and the standard Al/NH4ClO4 propellant (similar to 7x).

Automated summary

By combining experimental analysis and computational calculations, this study investigates the energy release mechanisms of ammonia borane with different chemical oxidizers. The results show that the ammonia borane/NH4ClO4 system exhibits significantly higher energy release rates compared to ammonia borane/KClO4.