High conductivity and chemical stability of BaCe1−x−yZrxYyO3−δproton conductors prepared by a sol–gel method

Abstract

High-temperature proton conductors are promising as electrolytes for intermediate-temperature solid oxide fuel cells. Among them, BaCeO₃-based materials have high proton conductivity but rather poor chemical stability. In contrast, barium zirconates are rather stable, but have poorly reproducible densities and conductivities. In this study, the investigation of BaCe_1−x−yZr_xY_yO_3−δ solid solutions (x = 0, 0.10, 0.20, 0.30, 0.40; y = 0.15, 0.20) was undertaken, with the final aim of finding a composition having both high conductivity and good stability. The influence of the modified sol–gel Pechini synthetic approach on the powder morphology, and of a barium excess on the densification were demonstrated. Single-phase perovskite powders were prepared and high density pellets were obtained at temperatures lower than those commonly employed. Stability tests demonstrated that the Zr introduction into doped barium cerate greatly enhanced the chemical stability, particularly for Zr ≥ 20%. The proton conductivities, measured in a humidified H₂/Ar atmosphere by impedance spectroscopy, were only slightly influenced by the Zr amount. Overall, BaCe_1−x−yZr_xY_yO_3−δ solid solutions having Zr ≈ 20–40% and Y ≈ 15–20% showed good chemical stability and high conductivity.