A high performance thermal expansion offset composite cathode for IT-SOFCs

Abstract

The introduction of negative thermal expansion (NTE) materials into cathodes with large thermal expansion coefficients (TECs) can not only reduce the mismatch of the thermal expansion behavior between solid oxide fuel cell (SOFC) modules, but also effectively improve their electrochemical performance. As the composite cathode of Sm_0.2Ce_0.8O_2+δ (SDC) based SOFCs, PrBa_0.5Sr_0.5Co₂O_5+δ–xSm_0.85Zn_0.15MnO₃ (PBSC–xSZM, x = 0, 10, 20 and 30 wt%) composites were prepared with high oxygen reduction reaction activity PBSC and NTE SZM. Phase boundaries with a thickness of 1–2 nm are observed at the junction of PBSC and SZM phases, indicating strong metallurgical bonding. The best comprehensive electrochemical performance is obtained for x = 20%, which exhibits a peak power density of 1.462–0.231 W cm⁻² at 923–723 K. The corresponding polarization resistance is only 0.018–0.764 Ω cm². In addition, apparent improvement of long-term working and thermal cycling stability can also be observed with 20% SZM addition in the PBSC cathode. With the studies of electrical conductivity relaxation of the cathode material and the distribution of relaxation time obtained in symmetrical cells, the corresponding mechanism is discussed. The results demonstrate that the introduction of SZM in the cathode of SOFCs should be indeed an effective strategy for the improvement of the performance and compatibility of SOFCs.