First-principles screening of the physical and hydrogen storage properties of Rh-based perovskites XRhH3 (X = Ca, Ba) for hydrogen storage applications

In this work, we conduct a comprehensive research of XRhH3 (X = Ca, Ba) hydrides using first-principles calculations, including their crystal structure, photoelectric, mechanical, dynamic, thermodynamic and hydrogen storage properties. Based on the Pugh's ratio (B/G) along with Poisson's ratio, it is concluded that XRhH3 (X = Ca, Ba) hydrides are both ductile ionic compounds. As evidenced by electronic property studies, these materials demonstrate metallic traits. Evaluating the formation energy and adherence to the Born stability criterion confirms that CaRhH3 and BaRhH3 possess both mechanical and thermodynamic stability. Analysis of the phonon dispersion curves reveals that they are both kinetically stable as well. The optical properties of XRhH3 (X = Ca, Ba) compounds demonstrate notably high polarizability and reflectivity. Our calculations indicate that the gravimetric hydrogen storage capacities of 2.07 wt% for CaRhH3 and 1.24 wt% for BaRhH3, respectively, with the corresponding dehydrogen temperatures of 423.02 K and 311.67 K, respectively. These findings suggest that CaRhH3 exhibits more favorable hydrogen storage potential than BaRhH3. Our study significantly deepens the understanding of perovskite hydrides' physical properties, and lays crucial theoretical groundwork and novel perspectives for designing high-performance hydrogen storage materials.