• DFT predicts stable tetragonal LiFeH 4 and LiCoH 4 complex hydrides with favorable structural and mechanical properties. • Both materials exhibit metallic, non-magnetic behavior with mixed ionic–covalent bonding. • Gravimetric and volumetric hydrogen capacities exceed U.S. DOE 2025 targets. • Low desorption temperatures suggest favorable hydrogen release characteristics. • Fe/Co substitution effectively tunes hydrogen storage and thermomechanical performance. The development of efficient, safe, and high-capacity solid-state hydrogen storage materials remains a major challenge for the realization of a sustainable hydrogen-based energy economy. This work reports a comprehensive first-principles DFT investigation of previously unexplored Li-based tetragonal complex hydrides, LiFeH 4 and LiCoH 4 , aimed at assessing their stability and multifunctional properties relevant to next-generation hydrogen storage technologies. Structural optimization and energetic analyses confirm the dynamical and mechanical stability of both hydrides. Electronic band structure and density of states calculations reveal a metallic character with finite electronic states at the Fermi level and non-magnetic ground states. Detailed charge density analysis indicates mixed ionic–covalent bonding, with strong metal–hydrogen interactions playing a key role in lattice stabilization. LiFeH 4 exhibits a high gravimetric hydrogen storage capacity of 6.03 wt% and a volumetric density of 194.91 kg/m 3 , while LiCoH 4 delivers 5.77 wt% and 186.77 kg/m 3 , respectively, both exceeding the U.S. Department of Energy 2025 targets. Notably, the hydrides show low hydrogen desorption temperatures, with LiCoH 4 desorbing at 203 K and LiFeH 4 at 285 K, indicating favorable hydrogen release behavior. Thermodynamic analysis, including zero-point energy corrections (0.9692 eV for LiFeH 4 and 0.8771 eV for LiCoH 4 ), Debye temperature, free energy, entropy, and heat capacity, further supports their stability over a wide temperature range. Mechanical and thermal assessments reveal higher hardness (19.27 GPa) and lattice thermal conductivity at 300 K (40.83 Wm −1 K −1 ) for anisotropic LiFeH 4 , whereas anisotropic LiCoH 4 exhibits improved ductility and lower thermal conductivity (17.74 Wm −1 K −1 ). These results demonstrate that LiFeH 4 and LiCoH 4 possess complementary hydrogen storage characteristics and highlights transition-metal substitution as an effective strategy for tuning material performance, providing valuable guidance for future experimental synthesis and practical application of Li-based complex hydrides.
Minhajul Islam (Sun,) studied this question.