Preparation And Properties Of CeO₂-based SOFC Solid Electrolyte Materials

With the continuous development of SOFC,the research on solid electrolyte materials is also advanced.Currently,the most studied oxygen ion conductors for aerobic ion conduction include ZrO₂-based,Bi₂O₃-based,CeO₂ based,La GaO₃-based electrolyte materials,etc.High working temperature and cost of ZrO₂-based electrolyte;Compared with ZrO₂-based electrolyte materials,Bi₂O₃-based electrolyte has higher ionic conductivity but electronic conductivity.La GaO₃-based electrolyte material is only suitable for electrolyte material under certain partial pressure of oxygen.Compared with other oxygen ion conductors,CeO₂-based electrolyte materials stand out.Traditional SOFCs require high operating temperatures and high operating costs,which limit the spread of SOFCs in practical applications.To sum up,the advancement of electrolyte materials with higher conductivity at low temperature（300℃-800℃）is the core and key of our current research work.However,CeO₂ base materials are easy to be reduced to produce Ce³⁺under high temperature or reductive atmosphere conditions,which leads to electronic conductivity and reduces the electric properties of batteries.Research shows that the double doping of CeO₂ base（alkali oxide or Rare Earth oxide）will effectively inhibit the reduction of Ce⁴⁺.Therefore,based on previous studies on fuel cell crystallography and electrolyte doping theory,ternary rare earth metal ion doping modification of CeO₂-based electrolyte material was carried out in this research,and its chemical composition,physical properties,electrochemical performance and micromorphological analysis were systematically examined and evaluated.This study focuses on the doping modification of CeO₂ group,using C₆H₈O₇·H₂O（CA）and rare earth nitrate/oxide as raw materials,using sol-gel method to prepare Ce_0.8Sm_0.16A_xGd_0.04-xO_1.9-δ(A=Y³⁺,Pr³⁺,Dy³⁺,Ca²⁺,CSAG)series terpolymer doped mo dified electrolyte materials.The experimental synthetic samples were examed by TG-DTG,SEM,FT-IR,XRD,EIS and so on.The experimental consequence shows that th e cubic phase Ce_0.8Sm_0.16A_xGd_0.04-xO_1.9-δ（CSAG,x=0.00-0.04）oxide can be obtained by sintering at 1150-1300℃for 3 h,and the spatial point group is Fm-3m.CeO₂-based ceramic sheets prepared by sol-gel method have high relative density and compactnes s sintering performance of Ce_0.8Sm_0.16A_xGd_0.04-xO_1.9-δ（x=0.00-0.04）ceramic sheets is more than 95%.EIS analysis shows that the conductivity of Ce_0.8Sm_0.16Pr_xGd_0.04-xO_1.9(x=0.03,A=Pr³⁺),and the maximum conductivity isσ=0.0494(S·cm^-1),Ea=0.0354（e V）.the highest conductivity of Ce_0.8Sm_0.16Dy_xGd_0.04-xO_1.9(x=0.01,A=Dy³⁺),σ=0.0477(S·cm^-1),Ea=0.0902（e V）.The Ce_0.8Sm_0.16Ca_xGd_0.04-xO_1.9-δsystem(x=0.01,A=Ca²⁺),σ=0.0212(S·cm^-1),Ea=0.0564（e V）,Ce_0.8Sm_0.16Y_xGd_0.04-xO_1.9ceramic sheet(x=0.03,A=Y³⁺)reaches the maximum value at 800℃,σ=0.1446(S·cm^-1),Ea=0.0229（e V）.an d rare earth doping can effectively suppress the electronic conductivity.In this researc h,four rare earth ions,Y³⁺,Pr³⁺,Dy³⁺and Ca²⁺,were doped to modify cerium dioxide respectively.It was searched that the ionic conductivity of each system doped was dee ply enhanced,Among the four systems doped with rare earth ions,Ce_0.8Sm_0.16Y_xGd_0.04-xO_1.9(x=0.03,A=Y³⁺)system has the highest ionic conductivity,which also showed t hat the doping modification of rare earth ions could significantly improve their electric al properties.Ba In_0.3Ti_0.7O_2.85（BITO）powder was also synthesized by high temperature solid state reaction method.Ce_0.8Sm_0.16A_xGd_0.04-xO_1.9-δ(A=Y³⁺,Pr³⁺,Dy³⁺,Ca²⁺,CSAG)systems,which have the highest conductivity,were combined with Ba In_0.3Ti_0.7O_2.85ceramic slices.Prepared CSAG-BITO composite electrolyte material,through the characterization analysis,experimental study found that,In Ce_0.8Sm_0.16Y_0.03Gd_0.01O_1.9-Ba In_0.3Ti_0.7O_2.85 this complex system,When the molar ratio of BITO is 15%,the conductivity of the composite system is the highest.the largest conductivityσ=0.0126(S·cm^-1),At this point,the activation energy Ea=0.0885（e V）,The thermal expansivity of the CSYG-BITO composite system is minimum,TEC=9.13(×10^-6℃^-1).The conductivity of pure Ba In_0.3Ti_0.7O_2.85,σ=0.0026(S·cm^-1),and the conductivity of CSYG-BITO composite modification is significantly upper than that of pure BITO,which contributes to oxygen ion conduction.In summary,it can be seen from the results of this study that the previous characterization data show that the solid electrolyte modified products can show high ionic conductivity in the range of medium and low temperature after CeO₂ group doping or compound modification.It is expected to provide useful experimental reference for the commercialization process of low temperature in SOFC.