Study On Performance Optimization Of Cathode Material Based On Dual Phase Mixed Conductor Solid Oxide Fuel Cell

Solid oxide fuel cell（SOFC）is a device that can directly convert chemical energy into electrical energy.It has the characteristics of high energy conversion efficiency,clean product,wide range of fuel adaptation and all-solid structure.Cathode material as one of the important components of SOFC,its performance directly affects the performance of the cell in low temperature.The perovskite structure Sr Fe O_3-δcathode material shows excellent electrochemical performance at high temperature,but its performance at medium and low temperature needs to be further improved.In this paper,based on the advantages of Sr Fe O_3-δcathode material,YFe O₃ material was introduced into it for surface modification to improve the reaction rate of cathode surface,and the performance of the cathode at low temperature was analyzed.At the same time,the effects of different preparation methods on the properties of dual-phase cathode materials were studied,and the phase structure,expansion,electrical conductivity and electrochemical properties of the materials were evaluated.The main contents are as follows:Two phase mixed electrode materials Sr Fe O₃ and YFe O₃ were synthesized by citric acid-ethylenediamine tetraacetic acid（EDTA）combustion step by step.After mixed in different proportions,the phase structures of Sr Fe O₃ and YFe O₃ were complex of cubic perovskite and orthogonal perovskite.With the increase of YFe O₃,the orthogonal structure gradually occupied the dominant position.The thermal expansion coefficient and maximum conductivity decrease with the increase of YFe O₃.The surface specific impedance（ASR）decreases first and then increases with the increase of YFe O₃,and the activation energy increases.The single cell with the structure of Ni-YSZ|Zr O₂-8%Y₂O₃（YSZ）|Ce_0.8Gd_0.2O_1.925（GDC）|two-phase mixed electrode material was prepared,and the maximum power density first increased and then decreased with the increase of the proportion of YFe O₃.At the same test temperature（800℃）,when the cathode material is Sr Fe O₃:YFe O₃=75:25,the maximum power density is 1173.62 m W/cm²,and the polarization impedance（R_P）value is the minimum 0.09Ωcm².After testing,the cell did not appear delamination,peeling phenomenon,has a good long-term stability.The cathode material Sr_1-xY_xFe O_3-δ（x=0.1,0.25,0.5,0.65,0.75,0.9）was synthesized by citric acid-EDTA combustion method in one step.When x=0.1 and0.25,the powder showed a cubic perovskite structure.When the doping amount of Y was more and more,the proportion of orthogonal perovskite structure increased.With the increase of Y element doping,the thermal expansion coefficient and the maximum conductivity decreased gradually,while the activation energy decreased first and then increased.Compared with the mechanical mixing electrode powder,the thermal expansion coefficient,the maximum conductivity and ASR were relatively lower.Compared with the mechanical mixing method,when the cathode material is Sr_0.75Y_0.25Fe O₃ at 800℃,the maximum power density is 1353.27 m W/cm²,and the R_Pvalue is lower than 0.06Ω·cm².Cell has good long-term stability.The composite electrode material Sr_0.75Y_0.25Fe O₃-GDC with different mass ratio has been studied.The phase structure of Sr_0.75Y_0.25Fe O₃ and GDC can be kept stably at different temperatures.Compared with single-phase Sr_0.75Y_0.25Fe O₃,the thermal expansion coefficient of the composite electrode with different mass ratio decreases,the material surface specific resistance of the composite electrode decreases,and the activation energy of Sr_0.75Y_0.25Fe O₃:GDC=8:2 is lower,and the composite electrode has better catalytic activity.At 800℃,the maximum power densities with mass ratios of 8:2 and 7:3 are slightly improved.Cell has good long-term stability.