An approach towards next-generation hydrogen storage: a DFT study on A₂LiTiH₆ (A = K, Ca) perovskite hydrides

This study explores the structural, mechanical, hydrogen storage, optical and thermodynamic properties of the double perovskite hydride A₂LiTiH₆ (A = K, Ca) by means of density functional theory (DFT). With tolerance factors of 0.997 for K₂LiTiH₆ and 0.903 for Ca₂LiTiH₆, both compounds have a stable cubic Fm-3m symmetry. K₂LiTiH₆ and Ca₂LiTiH₆ have calculated formation energies of -1.182 eV and -1.037 eV, respectively, suggesting a favorable thermodynamic stability. K₂LiTiH₆ exhibits a gravimetric capacity of 4.38 wt% and a volumetric capacity of 19.12 g L^-1, while Ca₂LiTiH₆ exhibits a gravimetric capacity of 4.29 wt% and a volumetric capacity of 23.41 g L^-1. The desorption temperatures for K₂LiTiH₆ are 435.8 K and 380.4 K for Ca₂LiTiH₆, making both materials suitable for hydrogen release at moderately high temperatures. The mechanical analysis of both compounds showed that they are both mechanically stable, with moderate hardness (9.64-17.10 GPa) and brittleness (B/G ratios of 1.29 for K₂LiTiH₆ and 1.37 for Ca₂LiTiH₆). Electronic properties of both materials display metallic behavior, suggesting potential applications in optoelectronics. Furthermore, thermodynamic properties, such as Debye temperatures (447.2 K for K₂LiTiH₆ and 584.0 K for Ca₂LiTiH₆) and melting points (811.2 K for K₂LiTiH₆ and 1195.2 K for Ca₂LiTiH₆), indicate the robustness of these materials for practical hydrogen storage applications. In this comprehensive study, A₂LiTiH₆ (A = K, Ca) perovskite hydrides are identified as potentially viable candidates for hydrogen storage systems and energy harvesting technologies.