Hydrogen desorption behaviors of Γ-AlH₃: Diverse decomposition mechanisms for the outer layer and the inner part of Γ-AlH₃ particle

Aluminium hydride (AlH₃) is a promising hydrogen storage material because it possesses a high theoretical hydrogen capacity of 10.01 wt%. However, the stability and decomposition mechanism of some AlH₃ polymorphs (e.g., γ-AlH₃) still remain unclear. In this work, the hydrogen desorption behaviours of γ-AlH₃ with or without TiF₃ addition were investigated by hydrogen desorption measurement and thermal analysis. It was revealed that the decompositions of the outer layer and the inner part of γ-AlH₃ particle follow diverse decomposition mechanisms. The outer layer of γ-AlH₃ particle tends to decompose directly, while the inner part of γ-AlH₃ particle prefers to first transform to more stable α-AlH₃ and then decompose. TiF₃ addition significantly lowers the temperature for the direct decomposition of outer layer γ-AlH₃ by about 30 °C but scarcely impacts the decomposition of inner part γ-AlH₃, which further confirms the decomposition mechanism of γ-AlH₃. It was suggested that the particle size plays an important role in the thermal stability of γ-AlH₃. The results of this work will help understanding the decomposition mechanisms of other AlH₃ polymorphs for hydrogen storage.