Solid oxide fuel cells (SOFCs) have attracted considerable attention because of their high energy conversion efficiency (reach up to 80%), low emission of pollutants, and excellent fuel flexibility. Conventional SOFCs need to be operated at high temperature typically at ~1000 ℃ to obtain the required performance. This high operating temperature leads to the degradation of fuel cell performance, interfacial reactions among the components, and limited choice of materials. Therefore, intermediate temperature solid oxide fuel cell (IT-SOFCs) would be a development trend for the next generation of SOFCs which could be commercialized in the future. Lowing the operating temperature from traditional 1000 ℃ to 500~800 ℃ or even lower not only significantly prolongs the lifetime of materials and reduces the SOFCs system costs, but also provides a broader range for material selection. Therefore, it is necessary to develop a new electrode material with high electrochemical activity in intermediate temperature range to improve electrochemical performance. As one of the mixed ionic-electronic conductors (MIECs), the reaction sites of double perovskite materials extend the active sites from the three phase boundary to the entire exposed surface, which affords low polarization resistance and high performance at intermediate operating temperature. Meanwhile, due to the high ability of transporting oxygen ions, the low thermal expansion coefficient, good catalytic activity and high tolerance to sulfur poisoning and strong resistance against carbon deposition, the double-perovskite oxide becomes a promising electrode material for the IT-SOFCs. This review focuses on the structure stability, electronic and ionic conductivity as well as catalytic activity of perovskite materials. The main concerns about current double perovskite based electrode materials are summarized and the main future research directions are proposed.

Contents
1 Introduction
2 Solid oxide fuel cells
2.1 Introduction of SOFCs
2.2 Principle of SOFCs
2.3 Advantages of SOFCs
2.4 Problems of SOFCs
3 Cathode of SOFCs
3.1 LnBaCo₂O₆ layered double perovskite
3.2 Other Co-base double perovskite
3.3 Co-free double perovskite
4 Anode of SOFCs
5 Symmetric solid oxide fuel cells
6 Conclusion and outlook