A First-Principles Investigation of the Structural, Electronic, Optical, and Mechanical Properties of Hydrogen Storage Ordered Vacancy Double Perovskite X2MH6 Materials

The rising demand for clean energy, especially hydrogen, has heightened the need for efficient storage materials. Perovskites, with their unique structures, show great promise for hydrogen storage and optical uses. To identify promising candidates for hydrogen storage materials, the mechanical, electronic, and optical properties of four ordered vacancy double perovskite structures X₂MH₆ (Ba₂BeH₆, Ba₂MgH₆, Ca₂BeH₆, and Sr₂MgH₆) were predicted using density functional theory. These materials were confirmed to be stable, and their hydrogen storage capacity, mechanical properties, electronic structures, and optical performance were thoroughly analyzed. Ca₂BeH₆ demonstrated the highest gravimetric (6.32%) and volumetric (32.29 g·H₂/L) hydrogen storage capacity, showcasing its exceptional potential. It should be noted that the hydrogen storage capacities reported here are theoretical estimates based solely on structural models, and this study does not assess the practical storage and delivery performance of these materials. Its mechanical stiffness and near-isotropic properties further enhance its practicality. Electrical studies revealed all four materials are semiconductors, all of them are direct semiconductors. Optical properties were analyzed via dielectric functions, offering key insights for designing advanced hydrogen storage and optical materials.