Preparation,Microstructure And Properties Of Doped CeO₂-based Electrolyte Materials For IT-SOFC

High temperature sintering is the main method for preparing dense electrolyte films for solid oxide fuel cells（SOFCs）,but high temperature sintering gives rise to problems such as difficulties in co-sintering electrolyte and electrode materials and high manufacturing costs for SOFCs.while increasing the conductivity of the electrolyte through doping,the sintering temperature needs to be reduced.The sintering temperature can be reduced by adding transition metal oxides.Therefore,the addition of transition metal oxides to the electrolyte co-doped with rare earth metal oxides can ensure its high conductivity and reduce the sintering temperature.In this paper,Nd³⁺and Sm³⁺co-doped cerium oxide（SNDC）powders with different Fe doping levels were prepared by the sol-gel method and Fe doped SNDC bulks were prepared by dry pressing and sintering.The effect of Fe doping on the surface morphology,cross-sectional structure,sintering performance and electrical conductivity of the SNDC bulks was systematically investigated by using field emission scanning electron microscopy（FE-SEM）and X-ray diffraction（XRD）to characterise the microstructure and phase structure of the samples,respectively,and AC impedance spectroscopy to determine the ionic conductivity of the samples at 500～750°C.The results of the study indicate that:Gels prepared by the sol-gel method can be obtained from 0～2.5 mol%Fe doped SNDC powders by calcination at 600°C for 4 h.XRD analysis shows that several powders and their bulks obtained by sintering at 1000～1400°C are cubic Ce O₂.Under the present experimental conditions,the Fe doping allows the SNDC bulks to have the highest relative density while having fine grains.Doping with Fe results in the highest relative density of SNDC bulks with fine grains.Doping with 0.5 mol%Fe increases the relative density of SNDC（sintered at1400°C）from 92.82%to 94.73%undoped and increases the grain size from 0.7303μm to1.6127μm;when the doping is increased by 2.5 mol%from 0.5 mol%,the relative density decreases very slowly to 94.43%and the grain size increases to 1.6838μm.The sintering properties of SNDC were significantly improved by Fe doping.After sintering 0.5 mol%Fe doped SNDC pressed samples at 1000°C,1100°C,1200°C,1300°C and 1400°C for 5 h,With the increase of sintering temperature,the relative density of sintered bulks increases first and then decreases,and the maximum relative density reaches95.85%at 1200℃,which was higher than that of the non-Fe doped samples sintered at1400°C.The relative density of the bulks obtained（94.82%）indicates that doping with 0.5mol%Fe can reduce the sintering temperature of SNDC from 1400°C to 1200°C.For SNDC bulks sintered at 1200°C,doping with 0.5 mol%Fe increased the relative density from87.83%to 95.85%.The ionic conductivity of SNDC bulks was significantly increased by Fe doping,but decreased as the amount of Fe doping increased from 0.5 mol%to 2.5 mol%.For SNDC bulks sintered at 1200°C for 5 h,doping with 0.5 mol%Fe increased the ionic conductivity from 0.0433 S cm^-1to 0.0674 S cm^-1at 750°C;as the amount of Fe doping increased to 2.5mol%,the ionic conductivity decreased to 0.0463 S cm^-1.