Synthesis And Properties Of Ce_0.95-xM_xCa_0.02Bi_0.03O_2-δ（M=Dy,Pr） Electrolyte

Solid oxide fuel cell（SOFC）have the davantages of high power generation efficiency,no environmental pollution,and suitability to a variety of fuels.SOFC are widely used in a very wide range of applications in many fields.As a core component of SOFC,solid electrolyte plays a major role in SOFC.The yttria-stabilized zirconia（YSZ）electrolyte is difficult to meet the requirements of SOFC at intermediate temperature,a crucial of lowering the operating temperature for SOFC is selection or development of new type of electrolyte materials with high ionic conductivity at intermediate temperatures（500～700℃）.The doped ceria-based electrolyte material has higher electrical conductivity than that of YSZ at intermediate temperature.However,the doped ceria-based electrolyte materials exists the problems that part of Ce⁴⁺is reduced to Ce³⁺under low oxygen partial pressure to generate electronic conductivity.To improve the ionic conductivity of doped ceria-based electrolyte materials,it is proposed to study the doping of cerium oxide with alkaline earth elements or rare earth elements,in order to develop electrolyte materials with excellent performance and suitable for intermediate temperature SOFC.Dy,Bi,Ca multi-element doped CeO₂ and Pr,Bi,Ca multi-element doped CeO₂-based electrolytes have been synthesized via the sol-gel method.The phase structure,surface chemical state,surface and cross-sectional micromorphology,concentration of oxygen vacancies,band gap energy,coefficient of thermal expansion,and electrical properties are characterized using X-ray diffraction,X-ray photoelectron spectroscopy,scanning electron microscopy,Raman spectroscopy,ultraviolet-visible diffusive reflectance and absorption spectroscopy,thermal dilatometer,and AC impedance spectroscopy,respectively.By characterizing the structure and properties of the Ce_0.95-xDy_xCa_0.02Bi_0.03O_2-δ（CDCB,x=0,0.05,0.10,0.15,0.20）system electrolyte materials,the synthesized electrolyte powder is a single cubic fluorite structure and Ce mainly exists as Ce⁴⁺.With the increase in Dy³⁺dopant concentration,the concentration of oxygen vacancies and electrical conductivity first increase and then decrease.Dense sintered pellets were obtained after the samples were sintered at 1350℃for 5 h.At the composition of x=0.10,the concentration of oxygen vacancies maximizes at 700℃,the maximum electrical conductivity is 3.53×10^-2 S/cm,At the same time,the activation energy（E_a=0.79 e V）and the value of the band gap energy（E_g=2.85 e V）of this composition are the smallest.By characterizing the structure and properties of the Ce_0.95-xPr_xCa_0.02Bi_0.03O_2-δ（CPCB,x=0,0.05,0.10,0.15,0.20）syetem electrolyte materials.XRD results show that the as-prepared samples form a single-phase cubic fluorite structure.The lattice parameter values increase with increasing Pr dopant concentration.The Raman spectra showed that the Ce_0.85Pr_0.1Ca_0.02Bi_0.03O_1.915 composition displays the highest oxygen vacancy concentration.X-ray photoelectron spectroscopy（XPS）analysis revealed that Pr exists in the form of Pr³⁺and Pr⁴⁺states.The ultraviolet–visible diffusive reflectance absorption spectroscopy found that the band gap energy is minimum when Pr dopant concentration is0.10.In addition,the Ce_0.85Pr_0.1Ca_0.02Bi_0.03O_1.915 displays the highest total conductivity(σ_700℃=0.11 S/cm)and low activation energy（E_a=0.82 e V）,this value is far better than Ce_0.8Gd_0.2O_2-δ(GDC,σ_700℃=0.0113 S/cm,E_a=1.02 e V)and Ce_0.95Ca_0.02Bi_0.03O_1.915(σ_700℃=0.0042 S/cm,E_a=0.87e V)un-doped Pr at the same temperature.La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ（LSCF）cathode powder was also synthesized by sol-gel method.The structure of LSCF and its chemical compatibility with the optimal CDCB and CPCB electrolytes were characterized by XRD,the results show that LSCF has orthogonal perovskite structure and good chemical compatibility with the optimal CDCB and CPCB electrolytes.The electrochemical of（1-x）LSCF-x CDCB（x=0,10%,20%,30%,40%）composite cathodes sintered at 1050℃,1100℃and 1150℃are characterized using AC Impedance Spectroscopy.The results show that at 700℃,the composite cathode with a composition of 60%LSCF-40%CDCB has the smallest polarization resistance（0.14Ω·cm²）after sintering at 1050℃;similarly,the composite cathode with a composition of60%LSCF-40%CPCB has the smallest polarization resistance（0.08Ω·cm²）after sintering at 1050℃.The anode-supported single cell Ni-CDCB|CDCB|60%LSCF-40%CDCB was construct and test the output performance,the results show that the output power of the single cell is the largest at 700℃,and the maximum power density is0.45 W·cm^-2.Also,the electrolyte-supported single cell Ni-CPCB|CPCB|60%LSCF-40%CPCB was constructed and test the output performance,the results show that the output power of the single cell is the largest at 700℃,and the maximum power density is 0.14 W·cm^-2.The above results indicate that the compositions of Ce_0.85Dy_0.10Ca_0.02Bi_0.03O_1.915 and Ce_0.85Pr_0.10Ca_0.02Bi_0.03O_1.915 are promising as solid electrolyte materials for intermediate temperature SOFC.