Achieving controllable structure stability and enhanced hydrogen storage performance of LiGaH₄: A rational design...

Rational compositional engineering of complex hydrides emerges as an effective strategy to achieve high hydrogen storage capacity and enhanced thermodynamic stability. In this context, DFT simulations are employed to systematically explore the impact of Al substitution on the physical and hydrogen-storage properties of Li(Ga_1-xAl_x)H₄ (x = 0.25, 0.50, 0.75) hydrides. Phonon Dispersion analysis reveals a progressive improvement in the structural stability of the host compound with increasing Al concentration. It is worth mentioning that the Al-rich LiGa_0.25Al_0.75H₄ compound becomes dynamically stable over the entire Brillouin zone. The computed elastic constants for all Li(Ga_1-xAl_x)H₄ compositions fulfill the Born criteria, which confirm the elastic stability of the studied compounds. Interestingly, the Al-rich LiGa_0.25Al_0.75H₄ compound achieves the highest gravimetric hydrogen capacity (8.29 wt%) and volumetric capacity (∼97 gH₂L^-1), meeting US-DOE targets. Furthermore, the diffusion barrier of H^- ion has been computed along three different paths. This research work identifies LiGa_0.25Al_0.75H₄ as a particularly promising complex hydride and demonstrates that targeted Al substitution in LiGaH₄ is an effective strategy for engineering stable, high-capacity compounds for solid-state hydrogen storage.