Structural, Electronic, and Hydrogen-Storage Properties of Cubic Perovskite Hydride Mg3ZrH8: A First-Principles Study

The cubic perovskite hydride Mg3ZrH8 was investigated using density functional theory. The optimized lattice parameter is a = 4.7479 Å, giving a material-level gravimetric hydrogen storage capacity of 4.68 wt % and a volumetric hydrogen density of 125.1 kg H2 m–3. Phonon calculations show no imaginary frequencies, indicating dynamical stability, while the Pugh ratio (B/G = 2.53) suggests ductile mechanical behavior. Electronic structure analysis indicates metallic character with a dominant contribution from Zr 4d states, while population analysis suggests predominantly ionic H–Zr interactions. Ab initio molecular dynamics at 300 K for 10 ps shows no immediate structural reconstruction. The ZPE-corrected dehydrogenation enthalpy for the first hydrogen-release step is 32.93 kJ mol–1 H2, corresponding to an estimated 1-bar desorption temperature of 253 K using ΔS ≈ S°(H2,g). This temperature should be considered a screening-level estimate because solid-state entropy contributions are not explicitly included. Convex-hull analysis places Mg3ZrH8 at 54.17 meV atom–1 above the calculated hull, indicating metastability relative to the considered competing phases. Overall, Mg3ZrH8 shows promising material-level hydrogen-storage characteristics, although experimental studies are required to establish its phase stability, reversibility, and cycling performance.