First-principles study on physical and hydrogen storage properties of XYH3 (X = K, Rb, Cs) perovskite hydrides

Abstract

In this study, we have employed the density functional theory to analyze the hydrogen storage capacities, structural, mechanical, photoelectric, dynamical and thermodynamic properties of XYH₃ (X = K, Rb, Cs) compounds for the first time. The calculated formation energies, elastic constants, and phonon dispersion curves of XYH₃ show that they have thermodynamical, mechanical, and dynamical stabilities. Both the Cauchy pressure and the B/G ratio indicate brittle behaviors, and their stress-strain curves are also analyzed. Furthermore, it is found that they are all anisotropic compounds with ionic bonds. The band structures indicate that the XYH₃ compounds are metallic. Their optical properties reveal strong transmission in the blue-green wavelength band and a high refractive index in the visible range. Thermodynamic properties, including entropy, enthalpy, heat capacity and free energy as a function of temperature are studied. The desorption temperatures of different dehydrogenation paths are calculated, and the optimal desorption temperatures of KYH₃, RbYH₃, and CsYH₃ are 332, 317, and 295 K, respectively. The adsorption/desorption energies of hydrogen on the surface (100) of these materials are also studied. We expect this study will provide a valuable reference for further research on XYH₃ compounds.