Composite Cathode And Anodic Current Collecting Problem Of Intermediate-Temperature SOFC

Currently, intermediate-temperature solid oxide fuel cell (IT-SOFC) is the focus of global investigation. The serious polarization of the cathode within the intermediate temperature range of 700～800℃and the current collecting problems are the main cause of the performance degradation and power loss of IT-SOFCs. Therefore, this study investigated on the Co_0.8Fe_0.2O_3-δ(SCF)-La_0.45Ce_0.55O_2-δ (LDC) composite cathode and current collecting problems at the anode side of IT-SOFCs.First, solid state reaction method and Pechini method were adopted to prepare the SCF powders, in which no impurities were found according to the X-ray diffraction (XRD) analysis. In addition, particle size distribution of the SCF powders thus prepared was examined while polarization performance test and electrochemical impedance spectropy (EIS) were used to evaluate the electrochemical performance of cathodes screen-printed with those powders. Microstructure of the cathodes prepared with the SCF powders was observed by scanning electron microscope (SEM). Results demonstrated that SCF powders prepared by Pechini method heated at 800℃for 3h possessed the smallest particle size of 2μm and the SCF cathode prepared by them had the best electrochemical performance.Furthermore, influence of the sintering temperature and amount of the binder-ethylcellulose added on the SCF cathode performance was also discussed. Test results showed that the best sintering temperature for Co_0.8Fe_0.2O_3-δ (SCF) cathode fabrication was 1000℃and the best added amount of ethylcellulose added was 8 mass%. Moreover, composite cathode materials were prepared by mixing the SCF cathode materials with La_0.45Ce_0.55O_2-δ (LDC). Polarization performance test and EIS were adopted to examine the electrochemical performance of the mono-layer and double-layer composite cathodes. Results showed that the addition of LDC could not only efficiently adjust the thermal expansion coefficient (TEC) of the cathode to match with those of the electrolyte and sealants, but also increase the three phase boundary of the cathode reactions, thereby improving the electrochemical performance of the cathode. The mono- layer composite cathode with the LDC amount of 40 mass% showed the best electrochemical performance of a polarization current density of 782.6 mA·cm^-2 at the 0.1V overpotential and a polarization resistance of 0.11Ω·cm².Finally, the current collecting problem at the anode side was also studied. atmospheric plasma spray (APS) method and electrochemical deposition method were utilized to prepare the Ni protective coating on the surface of the interconnect at the anode side. SEM, XRD as well as energy dispersive X-ray (EDX) analysis were adopted to determine the composition of the scale formed on the interconnect surface. The efficiency of the Ni protective coatings prepared by different methods was evaluated through area specific resistance (ASR) and oxidization kinetics test in the anodic atmosphere. Results showed that the interconnect with the Ni protective coating prepared by APS method after oxidized in the anodic atmosphere at 800℃for 250h showed an ASR of 12mΩ·cm², which can meet the ASR requirement of interconnect. ASR examination was taken to choose the current collecting layer and support layer materials in the current collecting design. ASR of the whole anodic current collecting design in the anodic atmosphere at 800℃was below 34 mΩ·cm² in the 96h test.