La0.6Sr0.4Co0.2Fe0.8O3-δ/CeO2 Heterostructured Composite Nanofibers as a Highly Active and Robust Cathode Catalyst for Solid Oxide Fuel Cells.

The lack of highly active and robust catalysts for the oxygen reduction reaction (ORR) at the intermediate temperatures significantly hinders the commercialization of solid oxide fuel cells (SOFCs). Here, we report a novel heterostructured composite nanofiber cathode composed of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and CeO2 nanoparticles, synthesized by using a coaxial electrospinning technique, which exhibits remarkably enhanced ORR activity and durability as compared to single LSCF powder and nanofibers. This cathode achieves a polarization resistance of 0.031 Ω cm2 at 700 °C, approximately 1/5 of that for the LSCF powder cathode (0.158 Ω cm2). Such enhancement can be attributed to the continuous paths provided by nanofibers for efficient mass/charge transport and the interdiffusion of La and Ce at the heterointerface which leads to more oxygen vacancy formation. Furthermore, the anode-supported cell with the LSCF/CeO2 composite cathode shows excellent stability (0.4 V for ∼200 h at 600 °C) because of suppression of Sr segregation in LSCF by introducing CeO2 and the structure of heterogeneous nanofibers. These results indicate that the microstructure design of this heterostructured composite nanofiber for LSCF/CeO2 is extremely effective for enhancing ORR activity and stability. This finding may provide a new strategy for the microstructure design of highly active and robust ORR catalysts in SOFCs.