| At present,the main energy supply of China is from fossil fuels,and most of fossil energy consume in the field of thermal power,which leads to serious environmental problems such as air pollution,acid rain,water pollution and so on.In order to strengthen the construction of ecological civilization and meet people's increasing need of a better life,it is necessary for our country to improve the efficiency of energy conversion like using fuel cells and use more new energy such as nuclear energy,wind energy,solar energy.Solid oxide fuel cell(SOFC)has many advantages,such as high energy conversion efficiency,wide applicable fuel,low internal resistance,solid state structure.Thus it is considered to be one of possible method to solve the conflict problems of environmental protection and energy requirements.But the actual energy conversion efficiency of SOFC is less than the theoretical value of SOFC,which can be due to the internal resistance of SOFC.Considering the polarization resistance of cathode is the main source of the polarization resistance,reducing the cathode polarization resistance is very important to improve the efficiency of SOFC.Typical SOFC cathode materials are studied in this work.The relationship between microstructure and oxygen transport performance of LaO 6Sr0.4Co0.2Fe0.8O3-?(LSCF)was researched while one new cathode material(Bi doped La1.75Sr0.25NiO4+?)was also researched.The first chapter is introduction.It mainly introduces the basic situation and the working principle of SOFC,the analysis methods used in the research,and the paper's main work content.The second chapter explores the factors affecting the oxygen transfer performance of LSCF.The LSCF powders areprepared by three methods and are researched by some characterization methods such as ECR,SEM and BET to collecting the information of the properties of the powder and the oxygen transport performance after sintering.By controlling the variables in the process of sample preparation and researching the performance of these samples,some factors are confirmed that they can affect the test results of oxygen transfer performance of LSCF.Specificially,when the grain size of samples is largger,the values of kchem and Dchem are largger.What's more,the results of SEM-mapping show that different sintering temperture can influence the distribution of elements and may lead to different test results of kchem and Dchem.In a word,it is obvious that some factors like the grain size of sample and the dstribution of elements can influence the oxygen transport properties of LSCF.The third chapter explores the influence of doping Bi to La1.75Sr0.25NiO4+?(LSN).The powder of La1.65Bi0.1Sr0.255NiO4+?(LSN-Bi)is prepared by citric acid-EDTA complexometric combustion method.The thermal expansion experiment find that doping Bi can decrease the start sintering temperature from about 1000 ?to 775 ?.What's more,the results of ECR show that doping Bi could improve 66.67%of the surface exchange coefficient and improve 72.78%of the oxygen diffusion coefficient at 700 ?.After doping Bi,the interfacial polarization impedance is also decrease to one seventh of the original value.The results of XPS and iodine titration analysis find that bismuth doping will improve the interstitial oxygen content of LSN and increase the average valence of Nickel,which can accelerate the oxygen transfer process and reduce the polarization impedance to improve the electrochemical performance. |
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