Computational evaluation of comprehensive properties of MgX3H8 (X=Sc, Ti and Zr) compounds as effective solid-state hydrogen storage materials

In this study, the structural, mechanical, electronic, dynamic, thermodynamic, and hydrogen storage properties of MgX₃H₈ compounds (X = Sc, Ti, Zr) were systematically investigated using density functional theory (DFT). To the best of our knowledge, these compounds have not been previously reported in either experimental or theoretical literature. This work represents the first comprehensive investigation of the various physical and chemical characteristics of these materials. They were considered promising candidates for solid-state hydrogen storage applications. The calculated formation enthalpies, elastic constants, and phonon dispersion relations confirmed that MgX₃H₈ (X = Sc, Ti, Zr) compounds are thermodynamically, mechanically, and dynamically stable, indicating their potential synthesizability. Analysis of the bulk-to-shear modulus ratio (B/G), specific heat capacity at constant pressure (Cp), and Poisson's ratio revealed that MgSc₃H₈ exhibits brittle behavior, whereas MgTi₃H₈ and MgZr₃H₈ are ductile in nature. Additionally, key parameters such as hardness, melting temperature, Debye temperature, machinability index, and elastic anisotropy factor were calculated and thoroughly analyzed. Electronic band structure calculations indicated a metallic character for all three compounds, as the valence and conduction bands intersect the Fermi level along high-symmetry directions. The dynamic stability of the cubic phase was further supported by the phonon dispersion curves and partial density of states, both of which exhibited only positive frequencies. The gravimetric hydrogen storage capacities were estimated to be 4.60 wt.% for MgSc₃H₈, 4.38 wt.% for MgTi₃H₈, and 2.56 wt.% for MgZr₃H₈, with corresponding hydrogen desorption temperatures of 239.54 K, 241.76 K, and 303.87 K, respectively. These mechanical and hydrogen storage characteristics suggest that the investigated MgX₃H₈ compounds are promising candidates for use as host materials in solid-state hydrogen storage systems.