A Comparative Study Of BaCoO₃ And BaFeO₃ Based Triple-conducting Cathodes For Proton-conducting Solid Oxide Fuel Cells

The proton-conducting solid oxide fuel cell（H-SOFC）has been widely studied in recent years due to its unique advantages.However,the lack of cathode materials largely limits its commercialization.Since the operating temperature of H-SOFC tends to move toward lower temperatures,the development of cathode materials with high performance at lower temperatures becomes a key step for the large-scale commercialization of H-SOFC.In this paper,two typical oxygen ion-electron hybrid conductors BaCoO₃ and BaFeO₃were selected for doping modification and comparative study,aiming to develop triple-conducting cathodes while conducting a comprehensive study and analysis of the properties of these two materials.Two perovskite materials Ba Co_0.8Zr_0.1Yb_0.1O₃and Ba Fe_0.8Zr_0.1Yb_0.1O₃ were prepared and applied to single cells.A series of characterizations were carried out to test the morphology,structure,and performance of the single cells.The research methods and results in this paper are as follows:（1）Perovskite oxides BCZYb and BFZYb were synthesized by the method of sol-gel.By means of XRD,the material phase structures were tested,which showed that both of them are typical cubic structures and manifest excellent chemical compatibility with the electrolyte material BZCYYb under high temperature conditions.（2）The thermal match between the two materials and the electrolyte material BZCYYb was evaluated.The average value of thermal expansion of BCZYb was much higher than that of BFZYb in the high temperature range,and BFZYb showed better thermal match with BZCYYb.The results of thermogravimetric analysis and iodometry as well as XPS analysis showed that BCZYb possesses a higher proportion of oxygen vacancy concentration,which provided more reactive sites for the oxygen reduction reaction at the cathode and was conducive to obtaining better catalytic activity.The conductivity of BCZYb was measured by the four-probe method and the conductivity of BCZYb was higher than that of BFZYb in the temperature range of 100-800°C.（3）H-SOFC full cells were prepared by dry pressing method and drop coating.The electrochemical performance of full cells with BCZYb/BFZYb-BZCYYb cathode was investigated by the means of electrochemical impedance spectroscopy test and I-V curve test.The electrochemical impedance spectra revealed that the polarization of the cathode could occupy a large proportion of the full-cell impedance,and the processes of oxygen adsorption,dissociation,and diffusion occurring at the cathode largely determined the overall electrochemical reaction rate.With comparison to BCZYb,the polarization impedance of BFZYb-based single cell has a greater impact on the overall cell impedance,indicating that its catalytic activity needs further improvement.The BCZYb-BZCYYb composite cathode presents relatively higher power output,while the long-term stability of the single cell needs to be further tested and compared in order to evaluate the suitability of both for use as H-SOFC cathodes comprehensively.