This work uses density functional theory (DFT) computations to investigate the structural, electronic, optical, mechanical, thermodynamic, and hydrogen storage features of the novel ZBaGaH6 (Z =K, Rb, Cs) complex hydrides. All hydrides are dynamically stable, according to phonon dispersion studies, and crystallize in the cubic F4‾3m space group. Additionally, AIMD simulations at room temperature verify thermal robustness without structural deterioration. The impact of alkali metal substitution on band alignment and semiconducting character is shown by the electronic band structures, which display indirect band gaps. The VBM in ZBaGaH6 (Z =K, Rb, Cs) shows flat bands with heavy holes (-2.6 to -3.0 mₑ) from H-localization, while the CBM displays dispersive Ba-d/Ga-s hybridization (44-58% d-orbital). Alkali metals tune properties: Cs widens the gap most (2.4-3.6 eV) via relativistic effects, whereas K minimizes distortion. These materials combine stable H-bonding (VBM) with mobile electrons (CBM), making Cs variants ideal for storage and K versions better for fast cycling, outperforming traditional hydrides in tunability and band separation. The mechanical analysis confirms that all the compounds adhere to the Born stability criteria, indicating a reduction in stiffness as one moves from K to Cs. The evaluation of optical properties reveals high dielectric constants, strong absorption in the UV range, and tunable refractive indices; among the studied compounds, KBaGaH6 exhibits the highest optical activity. Based on the calculations, the hydrogen storage capacities are determined to be 2.40 wt% for KBaGaH6, 2.03 wt% for RbBaGaH6, and 1.75 wt% for CsBaGaH6. Our computational study demonstrates that ZBaGaH6 hydrides are thermally robust, with decomposition enthalpies of ~75 kJ/mol H2 yielding desorption temperatures of 302–309◦C. This stability is a key asset for their potential use in safe, solid-state hydrogen storage systems.

Title

ELECTROCHIMICA ACTA

Publisher

ELSEVIER

Publisher Country

United Kingdom

Indexing

Thomson Reuters

Impact Factor

5.6

Publication Type

Both (Printed and Online)

Volume

542

Year

2025

Pages

12