First principle study on the physical properties of ternary hydride perovskites XRhH3 (X=Li, Na, K and Rb) as hydrogen storage materials

Hydride perovskite materials show great potential in hydrogen storage applications. This work investigated the structure and physical properties of Rh-based ternary hydride perovskites XRhH3 (X = Li, Na, K and Rb) using first-principles method for the first time. All XRhH3 compounds are mechanically, thermodynamically and dynamically stable. The electronic properties prove that these materials all show metallic nature. The optical properties show that the XRhH3 materials have high dielectric function and refractive index. Mechanical properties indicate that LiRhH3 and NaRhH3 are ductile materials while KRhH3 and RbRhH3 show brittle behavior. Among these compounds, LiRhH3 and NaRhH3 demonstrate stronger bearing capacity of lateral deformation and stiffness, making them more suitable for hydrogen storage. The calculated hydrogen storage capacities of LiRhH3, NaRhH3, KRhH3 and RbRhH3 are 2.61, 2.29, 2.04 and 1.56 wt%, respectively. The hydrogen desorption temperatures are 415.6 K for LiRhH3, 363.7 K for NaRhH3, 268.2 K for KRhH3, and 178.1 K for RbRhH3, respectively. Thus, LiRhH3 and NaRhH3 have greater potential as hydrogen storage materials due to their higher stabilities and hydrogen storage capacities among these compounds. Our research not only enriches the research on the physical properties of perovskite hydrides, but also provides a valuable theoretical foundation and new options for the development of efficient hydrogen storage.