Synthesis And Properties Of Ce-doped SrCoO_3-? As Cathode Materials

Due to the energy crisis and environmental protection issues are increasing seriously,Solid Oxide Fuel Cells?SOFC?,as a clean and efficient new green power generation device,has a very broad application prospect.However,the traditional SOFC works at high temperature?900-1000°C?.The higher working temperature limits the commercial application of SOFC.Thus reducing the operating temperature to intermediate and low level?600-800°C?is an inevitable trend of SOFC development.By doing this,it not only helps to expand the range of materials for each component of the SOFC,prolong the service life of SOFC,but also to reduce the cost of SOFC production as well.However,as the operating temperature of the SOFC decreases,the polarization loss of the cathode will increase,resulting in a decrease in SOFC performance.Therefore,the research and development of SOFC cathode materials with high electrical conductivity,enthalpy stability,high catalytic activity and matching with thermal expansion coefficient of electrolytes at intermediate and low temperatures are crucial for intermediate temperature solid oxide fuel cells?IT-SOFC?.In this paper,the properties of a series of cathode materials of perovskite-type cathode materials Sr_1-xCe_xCoO_3-??x=0.05,0.1,0.15?and SrCo_1-y-y Ce_yO₃?y=0.05,0.1,0.15?were investigated,and the two materials were verified as a feasibility of the IT-SOFC cathode material,and comparing the effects of its structure and electrochemical properties when Ce was doped into different positions?A and B positions?of SrCoO_3-?.The Sr_1-x-x Ce_x CoO_3-??x=0.05,0.1,0.15?series cathode materials are synthesized by EDTA-citric acid combined method and its phase structure and electrochemical properties are tested.The results show that the rare earth element Ce in the A site forms a stable cubic perovskite structure,and the Sr_1-xCe_xCoO_3-?cathode material has good chemical compatibility with the medium temperature solid electrolyte material GDC.When x=0.15,CeO₂ precipitation is observed from the XRD pattern.When x=0.05 and 0.1,the conductivity of Sr_1-x-x Ce_xCoO_3-?in the temperature range of 600-800°C is 492-724 and 382-435 S·cm^-1,respectively.At 800°C,the interface resistance of the two materials on the GDC electrolyte is respectively 0.089 and 0.124?·cm².When the doping amount x=0.05,the best electrochemical performance of Sr_1-xCe_xCoO_3-?is the best choice.Adding GDC electrolyte to the Sr_0.95Ce_0.05CoO_3-?cathode material can significantly reduce the interfacial resistance of the GDC electrolyte.When the GDC is 30%,the interface resistance is the smallest,and the interface resistance is at least 0.017?·cm² at 800°C.The single-cell Ni-GDC/GDC/Sr_0.95Ce_0.05CoO₃-GDC based on Sr_0.95Ce_0.05CoO_3-?-GDC as the cathode has a maximum power density of 425 mW·cm^-22 at 700°C.SrCo_1-y-y Ce_yO_3-??y=0.05,0.1,0.15?series materials are synthesized by EDTA-citric acid complex method and evaluated as IT-SOFC cathode materials.The results show that the thermal expansion coefficient decreases significantly with the increase of Ce⁴⁺doping amount in the solid solubility range.The thermal expansion coefficient is as low as 13.46×10-6 K^-11 when y=0.1.However,the electrical conductivity of the material decreases with increasing Ce⁴⁺content,but both meet the minimum requirements for IT-SOFC cathode materials.In the temperature range of 600-800°C,the electrical conductivity of SrCo_1-y-y Ce_yO_3-?cathode materials with y=0.05 and 0.1 is348-589 and 319-389 S·cm^-1,respectively.At 800°C,the upper interface resistance of these two materials in GDC electrolyte is 0.102 and 0.361?·cm²,respectively.Adding GDC electrolyte to SrCo_0.95Ce_0.05O_3-?cathode material can significantly reduce the interface resistance on GDC electrolyte.When GDC is added at 30%,the interface resistance is the smallest.At 800°C,the interface resistance is the minimum of 0.023?·cm².SrCo_0.95Ce_0.05O_3-?-GDC was used as the cathode cell Ni-GDC/GDC/SrCo_0.95Ce_0.05O₃-GDC,and the maximum power density was 380 mW·cm^-2at 750°C.Comparing the results of Ce doping at different positions of SrCoO_3-??A and B positions?,it is shown that the A-site doping is more conducive to improving the conductivity and stabilizing the cubic perovskite structure,and the B-site doping is more effective in reducing the thermal expansion coefficient.Significantly,the two have different advantages,but they are all potential IT-SOFC cathode materials.