Synthesis Of La_0.6Sr_0.4Fe_0.8Co_0.2O_3-δ-Gd_0.2Ce_0.8O_2-δ Composite Cathode Materials By In-Situ Method And Research On Electrochemical Properities

Solid-oxide fuel cells (SOFCs) is considered as one of the most promising devices by converting chemical energy into electrical energy. However, the interfacial polarization resistances between electrolyte and electrodes increase dramatically as the operating temperature is reduced. Thus, the development of novel electrode materials and/or unique microstructures is one of the critical issues in the development of new generation SOFCs operating at 600-800°C. In this study, we investigated the composite cathode material La0.6Sr0.4Fe0.8Co0.2O3-δ(LSFC) and Gd0.2Ce0.8O2-δ(GDC) by in-situ sol-gel method, and the physical and electrochemical properties were characterized. The porous compsite cathode with honeycomb structure was synthesized by breath figures method. The composite electrode with such microstructure possesses the advantages of fast gas diffusion and extended triple-phase boundaries (TPBs).We synthesized LSFC-GDC compsite cathode material using in-situ method, and studied the influence of synthesis conditions on the properties of the composite material. The X-ray diffraction (XRD) analysis showed that the LSFC and GDC were successfully synthesized without impurities. The grain size of as-synthesized LSFC-GDC composite material was smaller than the grain size of LSFC obtained under the same synthesis conditions. Each phase was more regularly dispersed in the composite material than the material prepared by machincial mixing method. The TEC of LSFC-GDC was lower than LSFC and was close to the TEC of GDC, which indiacated the material was suitable for the SOFC cathode. After the comprehensive characterization of a variety of testing methods, ultimately the best synthesis conditions of the composite cathode material were determined: the best addition of GDC to LSFC was 50 mass % and the optimum calcining temperature of the material was 900℃.Furthermor, the calcining temperature and holding time were investigated. EIS were adopted to examine the electrochemical performance of the cathode calcined at different temperature and held for different time. The results showed that the best calcining temperature was 1000°C and the best holding time was 2 h. The polarization resistances of the LSFC-GDC composite cathode display the Rp values of 0.17Ω·cm² at 800°C, and 0.33Ω·cm² at 750°C. The power density of the cell with LSFC-GDC cathode was 1.07 W·cm^-2 at 800°C, when H2 flow rate is 50 ml/min.Finally, the porous LSFC-GDC composite cathode with honeycomb structure was fabricated by breath figures method. The factors that influenced the microstructure of the porous electrode were investigated. The microstructure of the cathode was observed by the SEM. The results indicated that through controlling certain temperature, huminity and polymer concentratation, the structure with pores of 10⁴0μm diameter were successfully fabritated, and sub-micron sized small holes were observed on the walls of the pores. When the pore diameter was 10μm and the calcining temperature was 1100°C, the polarization resistances of the LSFC-GDC composite cathode with honeycomb structure displayed the Rp values of 0.486Ω·cm² at 800°C.