Solid state synthesis of nano-sized AlH3 and its dehydriding behaviour

Abstract

Aluminum hydride (AlH₃) has a high gravimetric hydrogen capacity (10.1 wt%) and has attracted considerable attention due to its potential application for hydrogen storage. Up to now, almost all the routes developed for the synthesis of AlH₃ are energy-consuming and economically impractical for mass production. In this study, a cost effective route of solid state reactive milling was proposed to synthesize AlH₃ using aluminum chloride and cheap metal hydrides as starting reagents, with the LiH/AlCl₃, MgH₂/AlCl₃, and CaH₂/AlCl₃ reaction systems being experimentally investigated. The reaction progress and products during reactive milling were characterized by XRD and ²⁷Al NMR, and the morphology as well as the microstructure of the as-milled samples by SEM and TEM, respectively. It was found that nano-sized γ-AlH₃ could be synthesized by reactive milling with commercial AlCl₃ and nanocrystalline MgH₂ as reagents. Based on the XRD and NMR analyses as well as the TEM observation, the average size of the γ-AlH₃ phase in the as-synthesized γ-AlH₃/MgCl₂ nanocomposite was estimated to be about 8.5 nm. By an isothermal dehydrogenation test, the as-synthesized γ-AlH₃ was found to have a quite high hydrogen desorption capacity and fast kinetics, with a hydrogen desorption amount of about 9.71 wt% within 9080 s at 220 °C.