Chemical Stability of Proton Conducting BaZr1-xCexO3-Based Electrolytes in Pressurized CO₂-Containing Atmospheres

Acceptor doped barium cerates and zirconates are attractive electrolyte materials for use in various proton ceramic electrochemical devices such as fuel cells and hydrogen pumps. However, the long-term durability of these materials may be challenged by poor chemical stability in CO₂-containing atmospheres.
In this work, the chemical stability of the electrolyte material BaZr0.8Ce0.1Y0.1O3 (BZCY81) is studied in CO₂ and CO₂-H₂. Dense pellets prepared by sintering with NiO as a sintering aid were exposed to up to 10 bar CO₂(-H₂) for up to 150 h at elevated temperatures (400-800°C). After exposure, the pellet surface was analyzed by grazing incidence X-ray diffraction (XRD), scanning electrode microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) to search for BaCO3 formation. Overall, the electrolyte material displayed excellent stability towards CO₂. A small increase in apparent BaCO3 concentration on the pellet surface was only detected by XPS for samples aged in CO₂ and CO₂-H₂ at 800 °C. However, BaCO3 was not visible by XRD and SEM-EDS, indicating that the reactivity is limited to a nm-thick region of the electrolyte surface. The impact of processing conditions such as sintering temperature and use of NiO sintering aid on the electrolyte stability will be discussed.