An ab-initio study of physical properties of BeXH3 (X = Pd, Ag, and Cd) perovskites hydrides for hydrogen storage applications

Abstract

Novel perovskite hydride materials have emerged as promising candidates for hydrogen storage applications. In this study, density functional theory (DFT) was used to investigate the effects of substituting transition metals (X = Pd, Ag, and Cd) in BeXH₃ perovskite materials on their physicochemical properties and hydrogen storage performance. Thermodynamic stability was confirmed by negative formation energies (−0.872, −0.492, and −0.456 eV/atom for BePdH₃, BeAgH₃, and BeCdH₃, respectively), indicating the potential for experimental synthesis. Mechanical stability assessments revealed that BeAgH₃ and BeCdH₃ satisfy Born's stability criteria, whereas BePdH₃ exhibited mechanical instability. Electronic structure analyses, including the band structure and density of states, indicated metallic behavior for the studied compounds. Additionally, thermodynamic characteristics, such as entropy, Debye temperature, specific heat capacity at constant volume, and thermal expansion coefficients, were evaluated using the quasi-harmonic Debye model over a temperature range of 0–1000 K and pressure range of 0–20 GPa. The Debye temperature determines a gradual decrease with increasing temperature, while the heat capacity approaches the Dulong-Petit limit at high temperatures, consistent with stable solid behavior. The ab initio molecular dynamic results indicate that BePdH₃, BeAgH₃, and BeCdH₃ exhibit significant kinetic stability at 300 K. Furthermore, phonon dispersion calculations confirmed the dynamical stability of BeAgH₃, while BePdH₃ and BeCdH₃ exhibited imaginary frequencies. Hydrogen storage capabilities were further assessed, revealing reasonable gravimetric hydrogen capacities (2.49, 2.46, and 2.37 wt% for BePdH₃, BeAgH₃, and BeCdH₃, respectively), volumetric hydrogen storage capacities (126.06, 107.59, and 90.74 g H₂/L for BePdH₃, BeAgH₃, and BeCdH₃, respectively), and moderate hydrogen desorption temperatures (643.92, 363.03, and 336.68 K for BePdH₃, BeAgH₃, and BeCdH₃, respectively).