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

Abstract

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.