Preparation And Properties Of CeO₂-based Electrolyte For Solid Oxide Fuel Cells

Solid oxide fuel cells(SOFCs)as environmentally friendly and highly efficient energy conversion devices allow the conversion of chemical energy directly into electrical energy.The electrolyte is the most important part of SOFC.The performance of electrolyte largely determines the operating temperature and output power of SOFC.SOFCs have a high operating temperature causing the limiting the selection of materials,the decreased stability of battery components and high fabrication cost.Therefore,the development of electrolyte materials with excellent performance at intermediate/low temperatures is significance to the practical application of SOFC.This thesis mainly studies the effect of LSB addition and La2O3 and In2O3 co-doped on the structure and properties of CeO2-based electrolytes.First,Ce0.8Gd0.2O1.9(GDC)and Bi0.775La0.225O1.5(LSB)are prepared by sol-gel combustion method and solid-state reaction method,respectively.Then LSB-doped GDC(xLGDC)is prepared by mechanical mixing method.In addition,La2O3 and In2O3 co-doped CeO2 electrolyte powders are prepared by sol-gel combustion method.The XRD,SEM,space potential difference,conductivity and power density of xLGDC(x=0-20wt%)and Ce0.85La0.15-xInxO2-?(x=0?0.03)electrolytes are measured to investigate the effect of LSB and La2O3 and In2O3 co-doped on the microstructure and properties of Ce02-based electrolytes.The research results of electrolytes xLGDC(x=0-20wt%)with different content of LSB indicate that all the LGDC electrolytes are single phase without any other impurity phase exist.The relative density of LGDC electrolytes firstly increase with increasing the proportion of LSB(LSB<3wt%)and than decrease with increasing the proportion of LSB(LSB>3wt%).3LGDC has the highest ionic conductivity,the ionic conductivity of 3LGDC(1.47×10-2 Scm-1)is?75%higher than that of GDC(8.38×10-3 Scm-1)at 600?.The electrochemical performance of the single cells based on 10LGDC co-fired at 1300? can reach 655mW cm-2 at 700?.This electrochemical performance is?110%higher than that of the GDC-based cell.The introduction of LSB significently improve the open cell voltages(OCVs)of the single cells.Moreover,the long-term stability is maintained up to more than 100h,demonstrating high stability ofthe 10LGDC electrolyte.The research results of electrolytes Ce0.85La0.15-xInxO2-?(x=0?0.03)with different content of La3+ and In3+ indicate that La3+ and In3+ co-doped ceria have been prepared by a citric acid-nitrate sol-gel method.The results of the lattice parameter calculated by the hard sphere model are consistent with experimental data.Ce0.85La0.15-xInxO2-?electrolytes sintered at 1350?C have the relative densities density more than 96%and the relative density decreases and grain size of sintered pellets increases with increasing the In3+ concentration.Electrochemical analysis indicates that grains conductivity of Ce0.85La0.15-xInxO1.925 is pretty much the same with increasing the content of In,while the grain boundaries conductivity decreases with increasing the content of In.Moreover,La and In co-doped exhibits higher ionic conductivity and lower activation energy as compared with La singly doped ceria.The electrochemical performance of based on the CLI1 cells co-fired at 1350? can reach 635 mW cm-2 at 700?.