Synthesis And Modification Of Lanthanum Cobalt Oxide Cathodes For Intermediate-low Temperature Solid Oxide Fuel Cells

Solid oxide fuel cells(SOFC)have attracted much attention due to their all-solid structure without noble metal catalysts and good fuel adaptability.At present,the key problem of SOFC is that expensive sealing materials and connecting materials must be used in the system due to the higher working temperature.At the same time,the service life of the cells is greatly limited due to the higher working temperature.Therefore,reducing the working temperature of cells has become a major research focus.One of the key problems in lowering working temperature is the inadequate cathodic catalytic activity,especially at low temperature.In view of the inadequate catalytic activity of cathode materials,lanthanum cobalt oxide,a common cathode material,was studied in this paper.Several strategies were used to improve the cathode's catalytic activity and electrochemical performance.The main contents of this paper are as follows:(1)Lanthanum strontium cobalt oxide(LSC)cathode materials with different Sr content were prepared,and the effect of Sr doping on the electrochemical catalytic activity of LSC was investigated.Unlike the prediction,the effect of Sr doping on the properties of LSC materials is controlled by the crystal structure.Especially when the Sr doping content is between 0.3 and 0.8,the Sr doping content has no significant effect on the electrical and electrochemical properties of LSC materials.When Sr doping is no longer in this range,the electrochemical properties of LSC materials are inhibited due to the characteristics of two hexagonal structures.(2)In order to improve the electrochemical performance of traditional LSC cathode,a simple solution impregnation method was proposed.Experiments show that LSC nanoparticles produced by impregnation can significantly improve the oxygen reduction reaction(ORR)performance of LSC cathode.The polarization impedance of the impregnated LSC cathode is 0.07?cm² at 700?,and the power density of the full cell at700?is as high as 800 m W cm^-2,which is much higher than that of the original LSC cathode.The increase of surface area can explain most of the performance improvement.This simple impregnation strategy has been proved to be a potential way to improve the electrochemical performance of SOFC and reduce the operating temperature of SOFC.(3)To overcome the shortcomings of the traditional solution impregnation method,a new impregnation method for preparing high performance SOFC electrodes using high concentration sol was studied.The polarization impedance of the LSC cathode is 0.08?cm² at 650?.The maximum power density of the whole cell is 1400,970 and 590 m W cm^-2 at 650,600 and 550?,respectively.Compared with traditional solution impregnation,sol impregnation can obtain enough catalyst loading only once,which avoids the complex process of repeated impregnation operations and greatly speeds up the preparation process of cells.(4)The preparation of high performance composite LSC cathode by impregnation method was studied,which combines impregnation preparation of nano-cathode and impregnation surface modification.The first step is to use high concentration LSC sol precursor to ensure that enough LSC cathode load can be obtained by one dipping.In the second step,low concentration Ba_0.5Sr_0.5Co_0.8Fe_0.2O₃-?(BSCF)solution was used to prepare very fine nanoparticles coated on the surface of LSC cathode,which greatly improved the ORR catalyticability of LSC cathode.The polarization impedance of the composite LSC cathode is 0.07?cm² at 600?,and the maximum power density of the battery reaches 1350 m W cm^-2.By comparing different composite cathode materials,it was found that LSC materials with high conductivity and low catalytic activity were more suitable to be substrate materials,while BSCF materials with high catalytic activity and low conductivity were more suitable to be catalyst materials.Combining the advantages of the two materials,the composite cathode with higher performance can be obtained.This idea can be used as a universal principle to guide future fuel cell cathode material selection and battery structure design.