Preparation And Performance Researches Of Ceria Based Composite Electrolyte Materials For Solid Oxide Fuel Cells

The electrolyte is a key component of the solid oxide fuel cell. The conductivity and the sintering property of the electrolyte could be improved by optimizing the synthesis method, preparaing composite electrolyte and optimizing the sintering process in this paper.The key properties of SOFC electrolyte Ce0.8Sm0.2O1.90(SDC) are significantly affected by synthesis methods and the use of co-precipitators/organic ligands. In this paper, SDC powders were synthesized by co-precipitation method with ammonium carbonate, sodium carbonate and ammonium oxalate as co-precipitators, respectively, and sol-gel method with EDTA-citrate and tartaric acid as gelation ligands, respectively. Crystalline phase, particle size, sinterability and total conductivity were characterized by XRD, TEM, SEM and EIS. Dense SDC films were obtained when prepared with ammonium carbonate, ammonium oxalate and EDTA-citrate as co-precipitators or gelation ligand. The SDC synthesized by co-precipitation method shows higher grain boundary conductivity, while the SDC prepared with EDTA-citrate sol-gel method shows higher bulk conductivity. SDC films prepared by ammonium carbonate co-precipitation and EDTA-citrate sol-gel method show higher total conductivity at tested temperatures than SDC prepared by other methods, their conductivities are 0.015S·cm-1 and 0.018S·cm-1 at 600 ℃, respectively. It has been tentatively discussed on how the co-precipitators and organic ligands affect the properties of SDC.A novel composite electrolyte SDC-Li Na SO4 was prepared for intermediate temperature solid oxide fuel cells(ITSOFC). Its phase structure and cross-sectional morphology were examined by XRD and SEM, respectively, and its ionic conductivity was investigated by AC impedance in a temperature range of 400 oC~700 oC in air. It was found that the composite electrolyte was composed of two phases: crystal SDC and amorphous Li Na SO4. The conductivity of the composite electrolyte is significantly larger than that of SDC at intermediate temperatures(550oC-700oC) the conductivity slowly raises with temperature, the activation energy decrease significantly to 0.30 e V, and the values of the conductivity of SDC-Li Na SO4 are notabily higher than those of SDC and previously reported SDC-Li Na CO3. For example, the conductivity of SDC-Li Na SO4 is 0.217 S·cm-1 at 550 oC, 25 times higher than the value of SDC, and 3.2 times higher than that of SDC-Li Na CO3. The results indicate that the ionic conducting mechanism changes in composite electrolyte due to the melting of the sulfate second phase, and the diffusion and transmission of ions are accelerated.The sintering property of SDC is improved by adding Li2CO3, Li NO3 and the Li2SO4 as sintering aids, also contrast with Na2CO3 and K2CO3. This paper discussed the ionic conductivity of the electrolyte material and the mechanism of sintering in low temperature with the impact of different sintering aids and process technology.