| Solid oxide fuel cells (SOFCs) are chemical-electrical energy conversion devices with the advantages of high working efficiency, low emissions and excellent fuel flexibility. The present research focus in the SOFC field is lowering the cell working temperature from high temperature of～1000℃to the intermediate-temperature (IT) range of600-800℃. IT-SOFCs have the advantages of structural stability, long cell duration time and reduction of fabrication and running cost. However, the cell performance also decreases with the lowering temperature due to performance degradation of the component materials of cathode, electrolyte and anode. In particular, polarization resistance of the cathode increases fast with the lowering temperature due to relatively high activation energy of the cathode reaction (oxygen reduction reaction, ORR), and becomes dominant in determining overall performance of the IT-SOFCs. Therefore, development of new cathode materials with high electrochemical reaction activities at the IT range of600～800℃is of great significance for practical applications of the IT-SOFCs.Cobalt-based perovskite oxides are important candidate cathode materials for IT-SOFCs because of high electronic-ionic conductivities and high catalytic activities for oxygen reduction reaction. The double-layered perovskite oxide PrBaCo2Os+ε has two A-site cations, Pr3+and Ba2+, and it proves that A-site cationic deficiency can help to improve the electrochemical activities of the perovskite oxides. In this work, the A-site Pr3+-deficent Pr1-xBaCo2O5+ε (P1-xBCO, x=0.00-0.10) oxides were synthesized with the sol-gel method and evaluated as the cathode materials of IT-SOFCs with respect to phase structure, stability, electrical conductivities and electrochemical performance, which change with the Pr3+deficiency contents (x).The x-ray diffraction (XRD) results have indicated that the P1-xXBCO oxides with Pr3+-deficiency contents of x=0.00-0.08were indexed as pure orthorhombic layered-perovskite structures, while some minor CO3O4impurity was found in the oxide with a high Pr3+-deficiency content of x=0.10, thus, the Pr3+-deficiency content in PBCO is limited by10%; besides, no obvious changes in lattice parameters with the various deficiency contents were observed. In order to check chemical compatibility between the cathode and electrolyte materials, powders of P1-xBCO and electrolyte Ceo9Gd0.1O1.95(GDC) in weight ratio of1:1were mixed thoroughly and calcined at1050"C for10h, followed by XRD measurement. The XRD results have demonstrated that P1-xBCO and GDC don’t react at1050℃and have high-temperature chemical stabilities. Electrical conductivities of the P1-xBCO oxides were measured by four-electrode method at200-800℃in air. It was found that all the samples have the conductivities higher than200s cm-1in the measured temperature range, meeting requirement of conductivities as a SOFC cathode. Besides, conductivities of P1-xBCO gradually decreased with the increasing Pr3+-deficiency content from x=0.00to x=0.05, and slightly increased at the bigger x=0.08, suggesting different charge compensation mechanism in P1-xBCO with various amount of Pr3+-deficiency. Electrochemical performance of the P1-xBCO cathodes was characterized by AC impedance measurement using the P1-xBCO/GDC/P1-xBCO symmetric cells. The results have demonstrated that introduction of the Pr3+-deficiency has greatly enhanced electrochemical activities of the P1-xBCO cathodes characterized by decreasing area-specific resistances (ASRs) with higher Pr3+-deficiency content from x=0.00to x=0.05. Among the studied samples. P0.05BCO (x=0.05) oxide with5%Pr3+-deficiency exhibits the best electrochemical performance. Its ASR values are0.113Ωcm2at600℃,0.054Ω cm2at650℃,0.027Ω cm2at700℃and0.016Ω cm2at750℃respectively. The ASR values at the low temperatures of600-700℃are～40%and～30%lower than the ASRs of the parent PBCO oxide (x=0) respectively. Such low ASR values have demonstrated that P0.05BCO is a promising cathode material of IT-SOFCs. |
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