Sythesis And Characterization Of The New Cathode Materials La_1.4Sr_1.6Mn₂O₇ Perovskite Manganites

Solid Oxide Full Cell(SOFC) is an advanced energy-conversion device which has characteristics of high efficiency,no-pollution,good to environment advantages, etc.The development and research for Intermediate Temperature Solid Oxide Full Cell(ITSOFC) is to reduce the operating temperature of the fuel cell stack to 500—800℃,not only reduce the overall system cost,but also increase the conversion efficiency of electric energy and the open-circuit voltage.As the key component of SOFC,cathode plays a very important role in the performance of the whole cell.Its structure,property and mechanism of reaction will affect behaviors of oxygen ions transmission and electrical conductivity.For the further improvement of cell performance,the development of high performance cathode material at intermediate temperature is critical.In this thesis,the cathode material La_1.4Sr_1.6Mn_2-xCo_xO₇(x=0-0.5) of ITSOFC was synthesized by a sol-gel method.We studied the properties such as the cell parameters,thermal expansion and electrical conductivity of samples(x=0) have been investigated.The structures of the compounds were investigated using powder X-ray diffraction,the result show that all structures of the samples belongs to the A₃B₂O₇ tetragonal structure with space group of I₄/mmm at a temperature of 1300℃.In order to study the chemical stability of electrode with electrolyte materials at high temperature,the sample was prepared by mixing thoroughly LSMO(x=0)with 8YSZ powders,and after heat-treating at 1300℃for 15h in air.XRD measurements,this result indicates that LSMO(x=0) has a good chemical compatibility with the 8YSZ electrolyte.We have studied the properties such as the cell parameters,thermal expansion and electrical conductivity of samples(x=0-0.5) with increasing of Co²⁺ content,It was found that the compositions exhibit the similar thermal expansion properties in the temperature of 200—800℃.The electrical conductivity of samples was found to obey the small polaron hopping mechanism and increase obviously.