Multifunctional Properties of Novel X₂FeH₅ Hydrides (X = Ca, Mg, Ba): A First-Principles Study of Hydrogen Storage, Electronic, Optical, and Mechanical Behavior

This study investigates the structural, hydrogen storage, mechanical, thermodynamic, electronic, optical, thermal, and phonon properties of the novel X₂FeH₅ hydrides (X = Ca, Mg, Ba) using first-principles calculations and molecular dynamics simulations. These hydrides crystallize in a stable tetragonal P4/nmm structure, with lattice parameters ranging from 4.55–5.58 Å along the a-axis and 6.27–7.87 Å along the c-axis. The mechanical and dynamical stabilities of the compounds are validated by their elastic constants and phonon dispersion spectra, respectively. Moreover, the negative formation enthalpies confirm their thermodynamic stability, with Ca₂FeH₅ exhibiting the highest stability, possessing a value of − 0.519 eV per atom. Electronic structure analysis reveals metallic behavior in Mg₂FeH₅ and Ba₂FeH₅, while Ca₂FeH₅ exhibits half-metallic behavior. Hydrogen storage capacities are calculated as 4.60 wt.% for Mg₂FeH₅, 3.56 wt.% for Ca₂FeH₅, and 1.50 wt.% for Ba₂FeH₅, with corresponding desorption temperatures of 240 K, 460 K, and 384 K, respectively, positioning Mg₂FeH₅ as particularly promising for practical use. Optical properties suggest suitability for optoelectronic applications. Mechanical analysis indicates brittleness across all materials, with Mg₂FeH₅ exhibiting the highest thermodynamic stability. These findings highlight X₂FeH₅ hydrides as promising candidates for sustainable energy storage and optoelectronic applications, warranting further experimental and theoretical exploration.