Fundamental Study on Mechanisms of Thermal Decomposition and Oxidation of Aluminum Hydride

Aluminum hydride (AlH₃) has great potential for a variety of propulsion and energy-storage applications. In this study, the ReaxFF reactive force field molecular dynamics simulation is employed to investigate the fundamental reaction mechanisms of thermal decomposition and oxidation of AlH₃. The effects of an oxide layer and/or defect are examined, and the detailed process and mechanism of H₂ and H₂O formation are illustrated. With the presence of an oxide layer, H₂ production of core-shell AlH₃ during the thermal decomposition is slower than that of bare AlH₃. As far as oxidation is concerned, any defect enhances the initiation of core-shell AlH₃ oxidation and accelerates the oxidation at the early stage of the reaction. Additionally, the presence of O₂ promotes the production of OH. Both thermal decomposition and oxidation of core-shell AlH₃ show significant H₂O production, and H₂O is preferentially formed compared with H₂ at the beginning of the reaction. The results reveal that the structural evolution of core-shell AlH₃ during the thermal decomposition and oxidation proceeds in three distinctive stages, respectively. It is found that during the oxidation, dehydrogenation and oxidation proceed simultaneously although the oxidation rate is limited during the dehydrogenation period.