Preparation And Properties Of Nb⁵⁺,Sc³⁺ Doped La_0.5Sr_0.5Co_0.8Cu_0.2O_3-δ Cathode Materials

The Solid oxide fuel cells（SOFCs）are energy conversion devices that convert the chemical energy of a fuel into electrical energy.SOFCs mainly consist of three parts:cathode,electrolyte,and anode.The reduction reaction of oxygen is mainly carried out on the cathode,including the processes of diffusion of oxygen,adsorption,oxidation,and conduction of ions and electrons.The conventional La_0.5Sr_0.5CoO_3-δgroup has become a hot research topic due to its excellent ion and electron transport properties and catalytic activity.However,the La_0.5Sr_0.5CoO_3-δcathode has two major drawbacks:first,the presence of Co increases the material’s coefficient of thermal expansion（TEC）,and leads to cell cracking and affects the cell’s long-term stability;second,surface Sr segregation leads to lower cell performance and a shorter service life.In recent years,doping perovskites with an appropriate amount of cations at the B position has improved the structural and compositional stability of cathode materials,improved the insufficient electronic conductivity,and improved the cathodic oxidation reduction reaction（ORR）activity.In this paper,Cu-doped La_0.5Sr_0.5Co_0.8Cu_0.2O_3-δ(LSCCu_0.2O_3-δ)base was used as the study system,and Nb⁵⁺and Sc³⁺were used as dopants.The effects of Nb⁵⁺and Sc³⁺on the structure and electrical properties of LSCCu_0.2O_3-δwere investigated to determine the optimal doping amount.La_0.5Sr_0.5Co_0.8Cu_0.2-xNb_xO_3-δ(LSCCu_0.2-xNb_xO_3-δ)and La_0.5Sr_0.5Co_0.8Cu_0.2-xSc_xO_3-δ(LSCCu_0.2-xSc_xO_3-δ)cathodes were prepared by a modified Pechini method.The prepared cathodes were characterized by X-ray diffraction（XRD）,field emission scanning electron microscopy（FE-SEM）and other means for phase analysis and microscopic morphology.Then the AC impedance spectra of materials were tested by electrochemical workstation.（1）A series of LSCCu_0.2-xNb_xO_3-δ（x=0.00≤x≤0.075）perovskite oxides were successfully prepared by doping Nb⁵⁺into LSCCu_0.2O_3-δ.The effects of Nb doping on the structure,thermal stability,and electrochemical properties of cathode materials were studied in detail.After Nb doping,the sample particles were more uniform,the communication between particles was better,and they had a good porous structure.At700℃,the polarization resistance（R_p）of LSCCu_0.15Nb_0.05O_3-δwas 0.065Ωcm²and the peak power density（PPD）of a single cell supported by the electrolyte was 518 mW cm^-2.The excellent electrical properties suggest that LSCCu_0.15Nb_0.05O₃-_δwas a very promising cathode material for IT-SOFC.（2）A series of LSCCu_0.2-xSc_xO_3-δ（x=0.00≤x≤0.04）perovskite oxides were successfully prepared by doping Sc³⁺into LSCCu_0.2O_3-δ.The effects of Sc doping on the structure,thermal stability,and electrochemical properties of cathode materials were studied in detail.After Sc doping,the surface oxygen content of the material increases,Sr segregation was inhibited,and the coefficient of thermal expansion（TEC）was reduced.At700℃,the R_pvalue of LSCCu_0.18Sc_0.02O_3-δwas only 0.47Ωcm²,and the PPD of a single cell of the anode reached 1165 mW cm^-2.Compared with LSCCu_0.2O_3-δ(R_p=0.086Ωcm²,PPD=598 mW cm^-2),R_pwas reduced by 45%and PPD increased by 94.8%,respectively.LSCCu_0.18Sc_0.02O_3-δwas a potential cathode material for IT-SOFCs.Both Nb⁵⁺and Sc³⁺can effectively reduce the polarization resistance of LSCCu_0.2O_3-δ,improve the ORR catalytic activity,and significantly improve the electrical properties of LSCCu_0.2O_3-δcathode.