Theoretical Investigation of Proton Diffusion in Dion–Jacobson Layered Perovskite RbBiNb2O7

Perovskite materials are considered to be promising electrolyte membrane candidates for electrochemical applications owing to their excellent proton- or oxide-ion-conducting properties. RbBiNb2O7 is a double-layered Dion–Jacobson perovskite oxide, with Pmc21 symmetry. In this study, the electronic structure and proton-diffusion properties of bulk RbBiNb2O7 were systematically investigated using first-principles calculations. The unique layered crystal structure of RbBiNb2O7 plays a crucial role in proton storage and proton conductivity. Different proton-diffusion steps in RbBiNb2O7 were considered, and the activation energies of the relevant diffusion steps were evaluated using the climbing image-nudged elastic band (CI-NEB) technique. The proton diffusion in RbBiNb2O7 presents a two-dimensional layered characteristic in the a-b plane, owing to its layered crystalline nature. According to the transition state calculations, our results show that the bulk RbBiNb2O7 exhibits good proton-transport behavior in the a-b plane, which is better than many perovskite oxides, such as CaTiO3, CaZrO3, and SrZrO3. The proton diffusion in the Rb–O and Nb–O layers is isolated by a higher energy barrier of 0.86 eV. The strong octahedral tilting in RbBiNb2O7 would promote proton transport. Our study reveals the microscopic mechanisms of proton conductivity in Dion–Jacobson structured RbBiNb2O7, and provides theoretical evidence for its potential application as an electrolyte in solid oxide fuel cells (SOFCs).