First-principles investigation of X-site cation effects on the hydrogen storage properties of XNi3H8 (X = Ti, V, Cr) hydrides

This research presents a comprehensive first-principles investigation into the physical and hydrogen storage characteristics of XNi 3 H 8 (X = Ti, V, and Cr) ternary hydrides using density functional theory. The optimized lattice parameters measure 4.192, 4.127, and 4.091 Å for the Ti, V, and Cr based compounds, respectively. The negative formation enthalpies confirm their thermodynamic feasibility. The TiNi 3 H 8 , VNi 3 H 8 , and CrNi 3 H 8 exhibit gravimetric capacities of 3.47 wt%, 3.43 wt%, and 3.42 wt%. Furthermore, the compounds demonstrate high volumetric densities of 184, 190, and 196 gH 2 /L. The calculated desorption temperatures of 222.20 K for TiNi 3 H 8 , 253.95 K for VNi 3 H 8 , and 301.93 K for CrNi 3 H 8 align closely with the U.S. Department of Energy operational requirements. Electronic structure analysis reveals a robust metallic nature as both spin channels intersect the Fermi level, with the density of states predominantly governed by the 3d orbitals of the transition metals. Mechanical evaluations establish that these materials are both ductile and anisotropic, while acoustic data and Debye temperature calculations highlight strong interatomic bonding and lattice stiffness. Optical analysis demonstrates significant absorption in the ultraviolet spectrum and high optical conductivity, indicating strong potential for optoelectronic applications. These findings, supported by stable thermodynamic profiles and structural integrity, suggest that the XNi 3 H 8 family represents a promising class of materials for efficient and reversible solid-state hydrogen storage applications.