Progress of Perovskites as Electrodes for Symmetrical Solid Oxide Fuel Cells

Symmetrical solid oxide fuel cells (SSOFCs), using the same material as both the anode and cathode, can reduce production costs and simplify the complex interface issues compared to conventional solid oxide fuel cells. The present challenge for SSOFCs is to explore suitable electrode materials that can maintain structural stability in both reducing and oxidizing atmospheres and exhibit good electrochemical activity toward both oxygen reduction and fuel oxidation reactions. Among the reported materials, the perovskites and perovskite-derived oxides are promising candidate electrodes for SSOFCs owing to their highly adjustable characteristics in structure and properties. In this review, we introduce the recently reported materials for SSOFC electrodes with their structural characteristics and property strengths/weaknesses. Attention is focused on the strategies for performance improvement and the mechanisms behind each solution. The correlation between the structural features, including defect formation, structure evolution, and interface modification, and the diverse properties, such as redox stability, electrical conductivity, and catalytic activity, are discussed. The performances of typical SSOFC electrode materials are summarized for comparison. Finally, the review is concluded with suggestions of possible directions for future research.