Structure And Properties Of Novel PrFeO₃-based Cathode Material For Intermediate Temperature Solid Oxide Fuel Cells

The worldwide energy crisis and environmental pollution problems can be alleviated by the commercial application of intermediate-temperature solid oxide fuel cells(500-800?,IT-SOFCs).However,the decrease in temperature has an adverse effect on the kinetics of the cathode oxygen reduction reaction.Developing novel active materials and optimizing microstructure are two advanced strategies to solve this problem.ABO₃type mixed ion and electronic conductor(MIEC)has high doping flexibility and excellent catalytic activity,making it become one of the most concerned cathode.Meanwhile,a heterogeneous composite material can be formed by adding a second phase.By making up for the shortcomings between the two,the purpose of performance optimization can be achieved.The sol-gel method and the solid-state mixing method were adopted to prepare two novel cathode materials respectively in this paper,namely:Pr_0.5Ba_0.5Fe_1-xNi_xO_3-?(x=0 and0.2,abbreviatedas:PBFandPBFN)cathodeand Pr_0.8Sr_0.2Fe_0.7Ni_0.3O_3-?-Pr_1.2Sr_0.8Fe_0.4Ni_0.6O_4+?(PSFN_113-214)heterogeneous composite cathode.Systematic study of the changes in crystal structure,thermal expansion behavior,surface chemical environment,microstructure and electrochemical performance of PBF cathode materials brought by Ni doping,as well as the influence of the presence of PSFN_113-214heterogeneous material interface on its structure and performance.The results indicate:(1)Ni has been successfully incorporated into the B site of PBF to cause lattice shrinkage.The PBF-based cathode has good high-temperature thermal stability in that it still maintains a cubic perovskite structure.And it has outstanding chemical compatibility and interfacial adhesion with Ce_0.8Gd_0.2O_1.9(GDC)electrolyte.The surface oxygen content and lattice oxygen release are enhanced by Ni substitution,which causes an increase in oxygen vacancy concentration,so it is conducive to ORR catalytic activity.Meanwhile,the particle size of the sample increases and the specific surface area decreases due to Ni doping,which reduces the ORR catalytic activity.At 700?,the polarization resistance of the PBFN cathode on the GDC electrolyte(0.0726?·cm²)is lower than PBF(0.122?·cm²),and the maximum power density of the corresponding single cell(0.529 W·cm^-2)is higher than PBF(0.260 W·cm^-2).After 80 h polarization,the open circuit voltage do not change significantly,indicating that the cell had good stability.PBFN has enormous prospects as an IT-SOFCs cathode because of its remarkable performance and brilliant stability.(2)PSFN₁₁₃shows a good orthorhombic perovskite structure.PSFN₂₁₄shows a typical K₂Ni F₄type tetragonal structure.After high temperature calcination,there is no element diffusion phenomenon between the two phases,so it has good chemical stability.PSFN₂₁₄is mixed with PSFN₁₁₃to form a heterostructure,which can increase the oxygen vacancy content and improve the oxygen ion transport as well as the specific surface area of PSFN₁₁₃.PSFN_113-214(5:5)has the best oxygen vacancy content and specific surface area,so the heterogeneous interface is the largest.At 800?,the polarization resistance of PSFN_113-214(5:5)is 0.029?·cm²,which is merely 24%of PSFN₁₁₃and 39%of PSFN₂₁₄.The corresponding maximum power density is 0.699 W·cm^-2,up to 1.44 times of PSFN₁₁₃and 1.24 times of PSFN₂₁₄.The voltage attenuation rate of the 100 h long-term stability test is only 0.0352%h^-1,which has the potential for long-term operation.