Preparation And Electrochemical Performance Of Ca₃Co₄O_9-δ-SDC Composite Cathode Impregnated With Electrolyte Materials

Owning to the features of low pollution, high efficiency and low costs, the intermediate solid oxide fuel cell (IT-SOFC) has been considered to be one of the most potential energy devices in recent years. Because Ca3Co4O9-δ has similar expansion coefficient with electrolyte, it has been the focus of study as the cathode of IT-SOFC in recent years.Based on the Ca3Co4O9-δ, in order to improve the length of the three-phase interface of cathode and electrolyte, this paper adopts the ion impregnation method to optimize the microstructure of cathode, and further improve the electrochemical performance of cathode.This paper prepared Ca3Co4O9-δ-SDC composite cathode via electrolyte impregnation method and investigated the phase structure, micro morphology and electrochemical performance of Ca3Co4O9-δ-SDC composite cathode by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and an electrochemical spectroscopy. The results show that Ca3Co4O9-δ-SDC composite cathode has good stability, the chemical reaction between them does not happen. Impedance test shows that at 800 ℃, the polarization impedance of the pure cathode Ca3Co4O9-δ is 0.3039 Ω·cm2, and a that of Ca3Co4O9-δ-SDC composite cathode is much lower than that of the pure cathode, its value is only 0.068 Ω·cm2, indicating that SDC electrolyte impregnation can greatly improve the electrochemical performance of the cathode.In order to further promote the electrochemical performance of Ca3Co4O9-δ-SDC composite cathode, we heated and stirred the impregnation solution, expecting to optimize the experimental scheme, and we prepared electrolyte-supported single cell. The results show that the electrochemical performance of Ca3Co4O9-δ-SDC composite cathode has been significantly improved. The value of impedance has further reduced to 0.035 Ω·cm2, the maximal power density of electrolyte supported single cell is 209 mW·cm-2 for pure phase Ca3Co4O9-δ and 662 mW·cm-2 for the composite cathode Ca3Co4O9-δ-SDC. Because Ca3Co4O9-δ has low electrical conductivity and dipping SDC can further reduce the electrical conductivity of cathode, Ag is used widely to improve the conductivity of cathode due to its high electrical conductivity. This paper tries to improve the cathode performance by dipping Ag on the composite cathode Ca3Co4O9-δ-SDC. However, the test result shows that the performance of composite cathode Ca3Co4O9-δ-SDC-Ag does not been optimized, the value of impedance is 0.09 Ω·cm2 and the maximal power density of the single cell is only 384 mW·cm-2. This may be associated with bigger Ag particle and smaller distribution range in cathode owing to the high sintering temperature. The composite cathode Ca3Co4O9-δ-SDC prepared through optimized impregnation method can obtain good cathode performance, and is very promising cathode materials of IT-SOFC.