First-principles insights into hydrogen storage potentials of XAlH3 (X = Si, Ge) perovskite hydrides

In this work, the structural, mechanical, thermodynamic, electronic, and optical properties of SiAlH 3 and GeAlH 3 perovskite hydrides is systematically investigated using first-principles density functional theory for hydrogen storage applications. The structural optimization reveals stable cubic phases for both compounds, supported by negative formation energies of −0.65 eV for SiAlH 3 and −0.49 eV for GeAlH 3 , indicating their thermodynamic stability and potential synthesizability. Ab initio molecular dynamics simulations confirm thermal stability at 300 K and 500 K, while phonon dispersion calculations show the absence of imaginary frequencies, verifying dynamical stability. Elastic analysis demonstrates that both materials are mechanically stable and exhibit ductile behavior, which is essential for maintaining structural integrity during hydrogen cycling. Electronic band structure and density of states analyses reveal metallic characteristics, facilitating efficient charge transport and enhanced hydrogen diffusion. Bonding analysis, including electron localization and population studies, indicates a mixed ionic–covalent nature, with strong H–Si/Ge covalent interactions stabilized by ionic Al–H bonding, supporting reversible hydrogen adsorption and release. Hydrogen storage evaluation shows gravimetric capacities of 5.21 wt% for SiAlH 3 and 2.95 wt% for GeAlH 3 , along with volumetric capacities of 100.4 and 95.2 g H 2 /L, and desorption temperatures of 477.63 K and 363.21 K, respectively. While SiAlH 3 offers higher hydrogen density, GeAlH 3 exhibits greater lattice flexibility, which may facilitate hydrogen release. Overall, these results identify SiAlH 3 and GeAlH 3 as promising candidates for efficient and reversible solid-state hydrogen storage and provide valuable insights for the design of next-generation perovskite hydrides with optimized storage performance.