Protonic-ceramic fuel cells (PCFCs) are emerging as promising energy-conversion devices, demonstrating superior performance compared to solid oxide fuel cells (SOFCs) for intermediate-temperature operation (400 - 600°C). This enhanced performance is attributed to the higher ionic conductivity and lower activation energy of protonic ceramic electrolytes, as opposed to traditional oxygen ion conductors used in SOFCs. Barium-based perovskite oxides, particularly acceptor-doped barium zirconate (BaZrO₃) and barium cerates (BaCeO₃) are commonly selected for PCFCs due to their high ionic conductivity. Barium zirconate focuses on improved chemical stability but suffers from low sinterability. In contrast, barium cerates are designed for low sintering temperatures, albeit with lower chemical stability under CO₂ and high steam concentration.

Adjusting the chemical stability and sinterability of BaZr_xCe_1-xO₃ solid solution, BaCe_0.7Zr_0.1Y_0.1Yb_0.1O_3−δ (BCZYYb7111) and BaCe_0.4Zr_0.4Y_0.1Yb_0.1O_3−δ (BCZYYb4411) are proposed based on specific applications. BCZYYb7111 is noted for its superior ionic conductivity and lower sintering temperatures, but it is less stable in CO2 environments. Conversely, BCZYYb4411, while showing slightly reduced ionic conductivity, offers remarkable chemical stability under various conditions. Both compositions, however, confront the challenge of barium evaporation during high-temperature sintering, leading to stoichiometric imbalances and the formation of secondary phases, which ultimately diminish their performance.

To mitigate barium evaporation, several methods are explored. A common approach involves placing an identical electrolyte pellet atop the primary cell during the high-temperature sintering process. However, this method is not feasible for configurations such as tubular geometries. As a result, tubular PCFCs may exhibit lower performance than planar cells, despite their unique advantages.

This presentation introduces the incorporation of excessive barium into BCZYYb4411 to counteract barium evaporation, specifically applied to tubular PCFCs. The study investigates the structural and electrochemical properties of Ba_1+xCe_0.4Zr_0.4Y_0.1Yb_0.1O_3−δ electrolytes with various levels of barium excess (x = 0, 0.1, 0.2, and 0.3). It is observed that an increase in barium concentration significantly enhances the sinterability of the electrolyte. This enhancement promotes densification at lower temperatures, effectively compensating for barium loss during sintering. The application of excessive BCZYYb4411 in the electrolyte of tubular PCFCs successfully boosts their electrochemical performance.