A comprehensive DFT study of XFe3H8 (X = Mg, Na, Sr) intermetallic hydrides for hydrogen storage applications

The structural, electronic, elastic, phonon, and thermodynamic properties of novel Fe-based complex hydrides XFe 3 H 8 (X = Mg, Na, Sr) were analyzed in detail using ab initio calculations. The spin-polarized band structures and density of states (DOS) reveal a pronounced metallic and ferromagnetic character, with the metallic host acting as an electron reservoir that stabilizes the interstitial hydrogen. Detailed charge density difference analysis confirms a consistent charge-transfer mechanism ( M → H δ - ) upon hydrogenation. The calculated average hydrogen binding energies, ranging from −0.024 to −0.270 eV/H, align perfectly with the required energy window for reversible solid-state storage. These hydrides demonstrate an inherent ductile behavior, as evidenced by Pugh’s ratio ( v > 1.75 ), Poisson’s ratio ( v > 0.26), and positive Cauchy pressure, ensuring mechanical robustness against pulverization. Phonon dispersion relations confirm their dynamical stability, while the localized high-frequency optical modes suggest potential for efficient thermal management. Notably, the compounds exhibit exceptional storage capacities, with gravimetric densities up to 4.06 wt% and record-high volumetric hydrogen densities reaching 193.97 kg/m 3 , significantly exceeding that of liquid hydrogen. These findings, combined with favorable estimated desorption temperatures (434–496 K), establish XFe 3 H 8 systems as high-performance, mechanically reliable candidates for compact hydrogen storage applications.