Synthesis and properties of La0.8Sr0.2Mn1−xRuxO3 as cathodes for solid oxide fuel cells

• Main Authors: Tai-Yang Lee, 李岱陽
• Other Authors: Jing-Chie Lin
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/34751359621996491146

碩士 === 國立中央大學 === 材料科學與工程研究所 === 99 === Chemical co-precipitation method was used to prepare the precursor which could be calcined to form La0.8Sr0.2Mn1−xRuxO3 (x = 0, 0.25, 0.5, 0.75, 1.0) as the cathode catalyst materials of the solid oxide fuel cells (SOFC). The effects of stoichiometric ratio between Ru/Mn and calcination temperature on the morphology, crystalline structure of the catalysts and on their specific surface area and cathodic behavior used in SOFC were of interest. Examination through field emission scanning electron microscope (FE-SEM) equipped with energy dispersive x-ray analysis (EDS), we could compare the morphology and composition for the powders and catalysts. Analysis by x-ray diffraction (XRD), we could distinguish the crystal structures between different types of catalysts. The specific surface area for different catalysts was measured by means of BET adsorption. The specific surface area was derived from different powders varying in Ru/Mn ratios sintered at various temperatures under various ratios of Ru/Mn. Chemical co-precipitation was carried out by titration a 0.2 M nitrate solution of precursors with 1.0 M sodium hydroxide solution. After filtration, the precursors were dried and calcined at 1000℃ for 5 h. Examination by FE-SEM depicted the calcined oxides are in porous morphology. Through analysis with XRD, we identified the calcined oxides as perovskite structure in which the chemical formula could be La0.8Sr0.2Mn1−xRuxO3 where x varies depending on the ratios of Ru/Mn. The perovskites may shift their crystal structure from trigonal to orthorhombic with increasing x from 0 to 1.0. The specific surface area of the calcined oxides decreases with increasing the Ru-concentration by checking the BET data. After making the calcined oxides as the cathode catalysts in a single cell, I-V polarization test and electrochemical impedance were conducted to evaluate the electrochemical performance. It was found that performance is the best for the catalyst with x equivalent to 0.25 (i.e., La0.8Sr0.2Mn0.75Ru0.25O3) that with the lowest impedance for the oxygen reduction reaction (ORR).