Compositional Effects on Proton and Oxygen Ion Transport in BaCoxFe0.8-xZr0.1Y0.1O3-δ (BCFZY)

BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY4411) has garnered heightened interest due to its triple-conducting capability, accessible synthesis, and structural stability. The electrocatalytic activity and H+/O2- transport behavior of BaCoxFe0.8-xZr0.1Y0.1O3-δ (BCFZY) can be tailored by fine-tuning the Co/Fe ratio, as recent studies suggest; however, the underlying mechanisms governing these properties remain unclear. Here, we use high-throughput density functional theory (HT-DFT) calculations and neutron diffraction analysis to investigate lattice ion vacancies, locate potential proton positions, and calculate H+/O2- transport pathways and migration energy barriers across the BCFZY solid solution series. We find that increasing Co content increases O vacancy concentration and lowers O2- diffusion energy barriers. While the proton concentration is extremely low (<0.002 per perovskite formula unit for the specific case of BCFZY4411), we identify a primary proton site, H1, occupying interstitial sites around oxygen ions, facilitating rotational and hopping diffusion with low-energy barriers that are largely insensitive to Co/Fe composition. Additionally, a secondary proton site, H2, may form near vacant Ba sites, creating deep potential wells that are likely to trap protons and impede diffusion. These findings underscore the tight interplay between material stoichiometry -Co/Fe ratio and Ba content─and the transport of O2- and H+ in BCFZY.