First-principles investigation of hydrogen storage potential in GeMgH3 and SiMgH3 hydride perovskites

The development of efficient, safe, and reversible solid-state hydrogen storage materials is essential for advancing a sustainable hydrogen-based energy economy. In this work, we present a comprehensive first-principles density functional theory investigation of the perovskite hydrides SiMgH 3 and GeMgH 3 , focusing on their structural, dynamical, mechanical, electronic, optical, and hydrogen storage properties. Both compounds are found to be thermodynamically and dynamically stable, as confirmed by negative formation energies and phonon spectra free of imaginary modes. Mechanical analysis reveals that both hydrides are ductile and mechanically robust, with SiMgH 3 exhibiting higher stiffness and stronger resistance to deformation compared to GeMgH 3 . Electronic structure calculations indicate metallic behavior with mixed ionic–covalent H–metal bonding, which enhances charge transport and supports reversible hydrogen mobility within the lattice. Optical properties further demonstrate strong dielectric response and efficient low-energy photon absorption, indicating favorable electronic polarization characteristics. Hydrogen storage analysis shows that SiMgH 3 exhibits superior performance, with a gravimetric capacity of 5.46 wt%, volumetric capacity of 91.6 gH 2 /L, and a moderate desorption temperature of 332 K, placing it close to practical operating conditions and the DOE target threshold. In contrast, GeMgH 3 exhibits lower hydrogen storage capacity and a higher desorption temperature, indicating reduced practical efficiency. These results establish SiMgH 3 as a highly promising perovskite hydride for hydrogen storage and provide critical atomistic insights to guide the design of next-generation hydrogen storage materials.