Wet Chemical Synthesis of Non-solvated Rod-Like α'-AlH₃ as a Hydrogen Storage Material

Aluminum hydride (AlH₃) is a promising candidate for hydrogen storage due to its high hydrogen density of 10 wt%. Several polymorphs of AlH₃ (e.g., α, β, and γ) have been successfully synthesized by wet chemical reaction of LiAlH₄ and AlCl₃ in ether solution followed by desolvation. However, the synthesis process of α'-AlH₃ from wet chemicals still remains unclear. In the present work, α'-AlH₃ was synthesized first by the formation of the etherate AlH₃ through a reaction of LiAlH₄ and AlCl₃ in ether solution. Then, the etherate AlH₃ was heated at 60°C under an ether gas atmosphere and in the presence of excess LiAlH₄ to remove the ether ligand. Finally, α'-AlH₃ was obtained by ether washing to remove the excess LiAlH₄. It is suggested that the desolvation of the etherate AlH₃ under an ether gas atmosphere is essential for the formation of α'-AlH₃ from the etherate AlH₃. The as-synthesized α'-AlH₃ takes the form of rod-like particles and can release 7.7 wt% hydrogen in the temperature range 120-200°C.