High-Capacity Novel XLi 3 H 9 (X = Ti, V, Cr) Hydrides for Hydrogen Storage: A First-Principles Study

The development of lightweight complex hydrides with high hydrogen-storage capacities and tunable desorption thermodynamics is crucial for advancing solid-state hydrogen-storage technologies. In this study, the structural, mechanical, electronic, magnetic, optical, thermodynamic, and hydrogen-storage properties of novel cubic XLi 3 H 9 (X = Ti, V, Cr) hydrides were systematically investigated using first-principles density functional theory (DFT) calculations. The optimized compounds exhibit negative formation energies of –0.77, –0.74, and –0.64 eV/atom, respectively, indicating energetically favorable formation relative to their constituent elements. All three hydrides satisfy the Born mechanical stability criteria and exhibit predominantly brittle behavior with mixed ionic–covalent bonding characteristics. Spin-polarized HSE06 calculations reveal indirect semiconducting behavior, with TiLi3H9 being non-magnetic, whereas VLi3H9 and CrLi3H9 exhibit magnetic moments of 1.0 and 2.0 μ B , respectively. The calculated gravimetric hydrogen-storage capacities reach 11.67, 11.22, and 11.08 wt%, accompanied by volumetric capacities of 151.7, 160.5, and 164.0 g H 2 /L for TiLi 3 H 9 , VLi 3 H 9 , and CrLi 3 H 9 , respectively. Phonon calculations reveal dynamical instabilities in the cubic phases at 0 K, whereas ab initio molecular dynamics simulations show structural persistence during 10 ps at 300 K. Depending on the proposed decomposition pathway, the estimated hydrogen-desorption temperatures range from 472.5 to 568.4 K or from 66.4 to 125.5 K, with CrLi 3 H 9 exhibiting the lowest predicted values. These findings highlight the exceptional theoretical hydrogen-storage capacities of XLi 3 H 9 hydrides and the potential for tailoring their hydrogen-release thermodynamics through transition-metal substitution, while further investigation of phase stability and reversible hydrogen cycling remains necessary.