Revealing hydrogen storage, thermodynamic, electronic, and mechanical aspects of perovskite hydrides GaXH3 (X = Si, Ge): First-principles approach

Recently, researchers have focused significantly on perovskite hydrides for hydrogen (H2) storage because of their capacity to store renewable energy effectively. This work theoretically investigates the structural, thermo-mechanical, electronic, and hydrogen storage characteristics of the hydrides GaXH3 (X = Si, Ge) to assess suitability for H2 storage technologies. The determination of formation enthalpies and elastic parameters for GaXH3 validates the thermodynamic and mechanical stability. Thermodynamic aspects against temperature and pressure reveal the stability and appealing characteristics for utilization in hydrogen storage. The evaluations of electronic aspects validate its metallic characteristics since intersecting conduction and valence states result in no bandgap. The bonding characteristics are obtained by electronic charge density analysis, which reveals a mixed covalent-ionic nature in GaXH3 hydrides, indicating both materials likely require increased temperature for H2 desorption. The mechanical characteristics reveal that hydrides GaXH3 exhibit brittleness by Pugh's ratio (<1.75) and Poisson's ratio (<0.26) with greater compression resistance and stiffness, making them preferable for the storage of hydrogen. The hydrogen storage capacities of GaSiH3 and GaGeH3 are 3.00 wt% and 2.08 wt%, with desorption temperatures of 625.88 K and 440.60 K, respectively. The calculated volumetric capacities (100.13 g.H2/L for GaSiH3 and 90.45 g.H2/L for GaGeH3) are excellent and far exceed the DOE target (40 g.H2/L). Notably, GaSiH3 reveals a higher storage capacity, and GaGeH3 demonstrates a lower desorption temperature. These results indicate that hydrides GaXH3 (X = Si, Ge) are a promising choice for hydrogen storage technologies. Furthermore, our research enhances the understanding of the physical features of perovskite hydrides and offers a significant theoretical framework and novel alternatives for advancing adequate hydrogen storage.