The Effect Of Surface And Interface Microstructure On The Catalytic Properties Of SmBaCoCuO_5+δ For Oxygen Reduction Reaction

Solid oxide fuel cell（SOFC）is an all-weather distributed off grid power generation technology,which has a series of advantages,such as high energy conversion efficiency,wide range of fuel use,no use of precious metals and environmental friendliness.It has a wide application prospect in data center,communication base station,smart home,large shopping mall,electric ship,large transport vehicle,UAV and pithead power station.Cathode polarization and high ohmic impedance are the key factors that restrict the application of SOFC.In the past few decades,high-strength researches have been carried out and a large number of high-performance cathode materials have been reported.However,traditional cathode powders such as(La_0.75Sr_0.25)_0.95Mn O_3±δ^[1]and La_0.6Sr_0.4Co_0.2Fe_0.8O_3+δ^[2]are still used in commercial stack.This is mainly because the polarization and ohmic resistance of SOFC cathode are the extrinsic parameters of cathode materials,which depend not only on the physical and chemical properties of cathode materials,but also on the microstructure of cathode/electrolyte interface and the surface microstructure of cathode materials under actual working conditions.However,up to now,the research on cathode materials is very little.Our previous results show that Sm Ba Co Cu O_5+δis a very attractive cathode material.For example,it has good thermal matching with electrolyte(thermal expansion coefficient 15.9×10^-6K^-1)and high oxygen catalytic activity（0.078Ωcm²@750℃）.In this view,this paper will take Sm Ba Co Cu O_5+δas the research object,and systematically explore the influence mechanism of surface microstructure of Sm Ba Co Cu O_5+δon its oxygen catalytic performance.The main work and results are as follows:（1）Effect of interface microstructure on the catalytic performance of SBCC:SBCC and Gd_0.1Ce_0.9O_1.95（GDC）have good chemical compatibility at 900℃,but when the temperature is higher than 950℃,elements will diffuse each other,leading to the sintering growth and cell shrinkage of SBCC grains.At the same time,the sintering growth and lattice strain of GDC grains increase.The interdiffusion between SBCC and GDC leads to a large deviation between the electrochemical performance of the cathode characterized by EIS and its actual catalytic activity for oxygen.The specific performance is that ASR of cell950 gradually decreases from70.191Ω·cm²（350℃）to 0.025Ω·cm²（800℃）with the increase of temperature.The ASR of cell1000 first increased（from 0.01Ω·cm²at 350℃ to 0.112Ω·cm²at 600℃）and then decreased（ASR was 0.021Ω·cm²at 800℃）.The EIS data of cell1000,cell1050SBCC950/GDC1000/SBCC950 and Au/GDC1000/Au were used to simulate the process of EIS testing symmetrical cells.It was found that the GDC produced partial electronic conductivity due to interface diffusion was the fundamental reason for this abnormal phenomenon.（2）Effect of surface microstructure on the catalytic performance of SBCC:We analyzed the EIS data of cell 900 sintered in air at 700℃ for 0 h and 540 h to explore the effect of Sm and Ba segregation on the electrochemical performance of SBCC.The results show that the composition segregation of A-site metal cations on SBCC surface will lead to the degradation of its oxygen catalytic performance.For example,at 700℃,the ASR of cell900-0h and cell900-540h are 0.549 and 0.978Ω·cm²,respectively.The polarization impedance of SBCC increases about 2 times due to the segregation of metal cations on the surface of SBCC during540 h high temperature sintering.The maximum output power of SBCC is about 0.12 w/cm²at700℃.The results of single cell and symmetrical cell show that the surface microstructure of SBCC is another key factor affecting its electrochemical performance.