Preparation And Properties Of Ce_0.8Gd_0.15-xNd_xca_0.05O_2-δ For Intermediate-Temperature Solid Fuell Cell

Solid Oxide Fuels Cell（SOFC）is a device that can continuously generate electricity with the advantages of high fuel utilization,low noise,easy mobility,and cleanliness.etc.With the growing energy and environmental crisis,SOFC has gained wide attention in today’s society.The electrolyte is the core of SOFC,and its performance directly affects the performance of SOFC.The conventional electrolyte,yttrium-stabilised zirconia（YSZ）,is adapted to high temperature environments,making the operation of SOFC in medium temperature environments severely affected.The doped Ce O₂-based electrolyte has become one of the popular topics for extensive research in recent years due to its good oxygen ion conductivity in medium temperature environments.However,Ce O₂-based electrolyte materials will partially reduce Ce⁴⁺to Ce³⁺under low oxygen partial pressure or reducing atmosphere,generating electronic conductivity and reducing the oxygen ion conductivity of Ce O₂-based electrolytes.In order to improve the electrical properties of Ce O₂-based electrolytes,this thesis investigates Gd³⁺,Nd³⁺and Ca²⁺co-doped(Ce_0.8Gd_0.15-xNd_xCa_0.05O_2-δ)materials and explores the possibility of using this electrolyte for medium temperature SOFC.The Ce_0.8Gd_0.15-xNd_xCa_0.05O_2-δelectrolyte powder was prepared by the sol-gel method.The effects of Gd³⁺and Nd³⁺doping on the structure and electrical properties of Ce O₂-based electrolytes were investigated at constant total doping amounts（20 mol%）of Nd³⁺,Gd³⁺and Ca²⁺.The physical structures of the synthesized samples were characterized by X-ray diffraction analysis（XRD）,Raman,X-ray photoelectron spectroscopy（XPS）and Ultraviolet Visible Spectroscopy（UV-Vis）.The samples were sintered at 1300°C for 5h,then observed by scanning electron microscopy（SEM）and the electrical properties of the component electrolytes were analysed by AC impedance analysis.The electronic conductivity of the optimum component electrolytes was measured using the Hebb-Wagner method.The results show that the electrolyte powder formed a single-phase solid solution with a cubic fluorite structure after calcinating at 800°C for 3h.The relative density of each component ceramic pellet reached higher than 95%.The electrolyte with a composition of Ce_0.8Gd_0.05Nd_0.10Ca_0.05O_1.875 had the highest oxygen vacancy concentration and the highest conductivity,its conductivity was2.04×10^-2 S·cm^-1 and the electronic conductivity was 7.48×10^-3 S·cm^-1 at 700°C.La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ（LSCF）cathode powder was prepared using the same method and mixed with the optimum component Ce_0.8Gd_0.05Nd_0.10Ca_0.05O_1.875 electrolyte in different proportions（0,10%,20%,30%and 40%）to prepare composite cathodes,which were analysed using XRD to study the high temperature chemical stability of the composite cathodes.Symmetric cells with the above proportions of composite cathodes as cathodes were constructed and calcinated at 1050°C,1100°C and 1150°C for 3h to measure the polarisation resistance.The results show that the LSCF-Ce_0.8Gd_0.05Nd_0.10Ca_0.05O_1.875 mixed powder showed good chemical stability after calcinating at 1150°C for 3h.The composite cathode composed of 70%LSCF-30%Ce_0.8Gd_0.05Nd_0.10Ca_0.05O_1.875 calcinated at 1050°C for 3h showed the smallest polarisation resistance,its value was 0.17Ω·cm² at 700°C.Using Ce_0.8Gd_0.05Nd_0.10Ca_0.05O_1.875 electrolyte as the electrolyte,the composite cathode with 30%electrolyte content was used as the cathode and Ni O-Ce_0.8Gd_0.05Nd_0.10Ca_0.05O_1.875 was used as the anode to assemble an anode-supported single cell,and the P-V-I curves and AC impedance of the single cell were measured in the temperature range of 500～700°C,the polarization resistance was calculated from them.The results show that the maximum power density of the single cell can reach 0.637 W·cm^-2 at the700°C and the polarisation resistance of the single cell was 0.08Ω·cm².