Performance Of BaZr_0.1Ce_0.7Y_0.2O_3-?electrolyte And Composite Electrode Materials For Proton-conducting Solid-oxide Fuel Cells

In recent years,intermediate-to-low-temperature solid oxide fuel cells?ILT-SOFCs?have garnered much attention due to their higher ionic conductivities and lower activation energies associated with proton conductors compared to oxygen-ion conductors.Therefore,proton-conducting solid oxide fuel cells?H⁺-SOFCs?offer ever-increasing potential for high-performance,lowed-temperature SOFC operation.Ba(Zr_0.1Ce_0.7Y_0.2)O_3-??BZCY7?has been widely used as protonic ceramic electrolyte in the H⁺-SOFCs,which combined the merits both the high proton conductivity of BaCeO₃-based electrolyte materials and the thermal stability of BaZrO₃-based materials.It is very important to study the effect of preparation methods of BZCY7 materials on the performance of SOFCs.In the meantime,it is essential to develop a suitable electrode material for use in BZCY7 proton-conducting electrolyte SOFCs.Based on the above considerations,we studied the effects of different synthesis routes on the properties of BZCY7 electrolyte material.We then investigated the feasibilityofthe(La_0.6Sr_0.4)_0.9Co_0.2Fe_0.6Nb_0.2O_3-?-xBa(Zr_0.1Ce_0.7Y_0.2)O_3-??LSCFN-xBZCY7,x=10,20,30,wt%?composite materials as symmetrical electrode materials for H⁺-SOFCs.The main contents and conclusions are summarized as follows:The dense BZCY7 electrolyte was prepared by traditional solid-state reaction method and sol-gel method.Among them,the BZCY7?BZCY7-SSR?synthesized by solid solid-state reaction method has a two-phase structure,which composed of rhombohedral crystal system with a small number of monoclinic phase;while the BZCY7?BZCY7-gel?synthesized by the sol-gel method has a single hexagonal crystal phase structure with a small grain size.The BZCY7-SSR reveals good structural stability in both wet hydrogen and carbon dioxide atmospheres;while the BZCY7-gel exhibits carbon dioxide intolerance.The thermal expansion,TGA,and electrical conductivity of BZCY7-SSR and BZCY7-gel electrolytes were tested.The results show that the BZCY7-SSR and BZCY7-gel undergo a reversible phase structure transition in the temperature range of 400-600°C.This change also results in a conduction mechanism transformation of BZCY7 from proton conduction at low temperature to oxygen ion conduction at high temperature.The average thermal expansion coefficient of BZCY7-gel is smaller than that of BZCY7-SSR,and the change in the slope of the thermal expansion curve caused by its phase transition is significantly smaller compared to BZCY7-SSR.The BZCY7-gel electrolyte exhibits higher electrical conductivity than that of BZCY7-SSR.Similarly,the cell with BZCY7-gel electrolyte delivers better power density in hydrogen fuel.Symmetric solid oxide fuel cell?SSOFC?has some distinct advantages such as low cost,simple structure configuration,and redox stability.However,little research work has been conducted on SSOFCs using BZCY7 as the electrolyte.Therefore,in this work,we investigated the feasibility of LSCFN-x BZCY7?x=10,20,30,wt%?composite materials as the H⁺-SOFC symmetrical electrodes.The BZCY7-gel was used as the electrolyte,which shows better conductivity in the above research results.The LSCFN materials have good chemical compatibility with BZCY7-gel in both oxidizing and reducing atmospheres.The LSCFN-xBZCY7 composite electrodes show good thermal expansion compatibility with BZCY electrolyte in 5%H₂/Ar and air atmosphere.The average TEC value of LSFCN-30BZCY(14.3×10^-6K^-1)is closest to that of BZCY7(13.0×10^-6K^-1)in 5%H₂/Ar atmosphere.The interfacial polarization impedance?ASR?of the LSCFN-xBZCY7 composite electrodes in air decreases with increasing BZCY content,but the result is the opposite in a humid hydrogen atmosphere.The ASR values of LSFCN-30BZCY in air and wet hydrogen atmospheres at 750°C are 0.131 and 0.044?cm²,respectively.The LSCFN-30BZCY7|BZCY7-gel|LSCFN-30BZCY7 single cell shows the maximum power density of 62 mW cm^-22 at 800°C with hydrogen as the fuel.