Insight of BaCe(0.5)Fe(0.5)O(3−) (δ) twin perovskite oxide composite for solid oxide electrochemical cells

One‐pot synthesized twin perovskite oxide composite of BaCe(0.5)Fe(0.5)O(3−) (δ) (BCF), comprising cubic and orthorhombic perovskite phases, shows triple‐conducting properties for promising solid oxide electrochemical cells. Phase composition evolution of BCF under various conditions was systematically investigated, revealing that the cubic perovskite phase could be fully/partially reduced into the orthorhombic phase under certain conditions. The reduction happened between the two phases at the interface, leading to the microstructure change. As a result, the corresponding apparent conducting properties also changed due to the difference between predominant conduction properties for each phase. Based on the revealed phase composition, microstructure, and electrochemical properties changes, a deep understanding of BCF's application in different conditions (oxidizing atmospheres, reducing/oxidizing gradients, cathodic conditions, and anodic conditions) was achieved. Triple‐conducting property (H(+)/O(2−)/e(−)), fast open‐circuit voltage response (∼16–∼470 mV) for gradients change, and improved single‐cell performance (∼31% lower polarization resistance at 600°C) were comprehensively demonstrated. Besides, the performance was analyzed under anodic conditions, which showed that the microstructure and phase change significantly affected the anodic behavior.