Interability Of BaZr_0.4Ce_0.4Y_0.2O_3-δ Proton-conducting Electrolyte And Performance Of Triple Conducting Ba_0.95La_0.05Fe_0.8Zn_0.2O_3-δ Cathode

Solid oxide fuel cells（SOFCs）have been widely concerned by researchers for their excellent Faraday efficiency,minimal environmental pollution,and strong fuel adaptability.However,due to the problems of material degradation and sealing caused by high operating temperature（¹000°C）,the commercialization of traditional SOFC has been greatly hindered.Researchers have made many efforts to reduce the operating temperature of SOFCs.An effective and attractive alternative is to develop proton-conducting SOFCs（H⁺–SOFCs）.Compared to the traditional ionic(O^2-)-conducting SOFCs(O^2-–SOFCs),the proton-conducting electrolyte has higher ionic conductivity and lower proton-conduction activation energy in the low temperature range（500°C–700°C）and hence the proton-conducting SOFC（H⁺–SOFC）is more suitable for practical applications.In addition,H⁺–SOFCs will form water on the cathode side of the cell at runtime,which helps achieve high fuel utilization and satisfactory Nernst potential.This thesis focuses on the research of electrolyte materials and cathode materials of H⁺–SOFCs.The first chapter briefly introduces the development background,working principle and components of SOFC,and expounds the development of electrolyte materials and cathode materials of H⁺–SOFCs.At the same time,it presents some urgent problems in H⁺–SOFCs.In the second chapter,in order to improve the sinterability of the proton-conducting electrolyte BaZr_0.4Ce_0.4Y_0.2O_3-δ（BZCY）more efficiently,we investigated the effect of different addition methods for the sintering aid of ZnO（¹wt.%）on the performance of the BZCY electrolyte.It is found that the internal doping of¹wt.%ZnO is an effective way for improving the sinterability of the BZCY electrolyte.The BaZr_0.4Ce_0.4Y_0.15Zn_0.05O₃-δ（BZCYZn）sample prepared by internal doping strategy exhibits higher density（⁹8%）and larger grain size after being sintered at 1350°C,as compared to the BZCY–ZnO sample prepared by the strategy of external addition of 1wt.%ZnO.The conductivity value of the BZCYZn sample is higher than that of the BZCY–ZnO sample at temperatures below 600°C,which is equivalent to the conductivity value of BZCY sintered at 1600°C for 5 h.The cell power density with a BZCYZn（⁴5μm）as the electrolyte reached 414.5mW cm^–2 at 700°C and stability over the 100h test period.Our results demonstrate that the improvement of the sinterability of the BZCY electrolyte is possible by means of internal doping strategy of ZnO using the traditional ceramic technology,which are easily processed.In the third chapter,a triple conducting Ba_0.95La_0.05Fe_0.8Zn_0.2O₃-δ（BLFZ）cobalt-free perovskite was evaluated as cathode for H⁺–SOFCs based on BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ（BZCYYb）electrolyte.BLFZ has a cubic perovskite structure and good chemical compatibility with BZCYYb electrolyte.The average thermal expansion coefficient of BLFZ is 20.4×10^-6 K^-1 at 30°C–1000°C.The polarization resistance（R_p）of BLFZ is decreased from 2.072Ωcm² in air to 1.334Ωcm² in wet air（3%H₂O）at 600°C due to the introduction of water.The single-cell power density with BLFZ–30wt.%BZCYYb composite cathode reaches 329 mW cm²at 750°C,and the corresponding R_p is 0.083Ωcm².On the basis of impedance analysis,the proton diffusion and incorporation to the electrolyte lattice(⁺_{（6（9）（4））→⁺（1）（6（80）,0）7}0)（87）0))and⁺（1）（6（80）,0）7)0)（87）0))→⁺（（77）6）,0)7)0)（87）0)))are the rate-limiting steps above 650°C,whereas the oxygen incorporated to the lattice(^2-(（5）→^2-（（77）6）,0)7)0)（87）0)))and proton bulk diffusion to the triple-phase boundary（⁺（（77）6）,0）7)0)（87）0))→⁺（）)are the rate-limiting steps below 650°C.The single cell with BLFZ–30wt.%BZCYYb composite cathode shows good stability at700°C during a 100 h test.The fourth chapter summarizes the work of the second and third chapters of the dissertation,and based on the research summary,the future research of H⁺–SOFCs is made.