Synthesis of (Ba0.5Sr0.5)1-XCaXCo0.8Fe0.2O3-δ Cathode Material of SOFC by GNP methode

• Main Authors: Chung-Kai Liao, 廖仲凱
• Other Authors: 余炳盛
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/7huq35

碩士 === 國立臺北科技大學 === 資源工程研究所 === 98 === Solid oxide fuel cell (SOFC) is a high-efficiency energy conversion device equipped with promising potential for development. Of the cathode materials for SOFC, BSCF (BaySr1-yCoxFe1-xO3-δ) is frequently used thanks to its excellent electron conductivity and superior catalysis characteristic. BSCF, however, reports several disadvantages, such as high thermal expansion coefficient, low electric conduction, and high cost. Using heterogeneous doping to facilitate changes in material characteristics, this thesis aims at synthesizing calcium-doped Ba0.5Sr0.5Co0.8Fe0.2O3-δ by the sol-gel combustion synthetic (GNP) method to form a new type of perovskite cathode material for improving the power generating ability of SOFC. By GNP method, the study successfully synthesized single-phase perovskite-type powdered BSCaCF, and the stoichiometry was verified by ICP-AES analysis. As the doping Ca has an ionic radius smaller than those of barium and strontium, results of XRD analysis indicated that the diffraction peaks of BSCaCF shifted to small angles. Using Unitcell to calculate the lattice parameters at various additions of the doping calcium showed that the lattice parameters of Ca doping at A site from 10% to 25% decreased from 3.9751 Å to 3.9356 Å. The lattice parameters stopped changing and impurity took place when the Ca doping exceeded 25%. The maximum amount of Ca doping at A site was accordingly estimated to be approximately 20%. The study selected three common electrolytes SDC, GDC and YSZ to perform chemical matching experiments with (Ba0.5-Sr0.5)0.9Ca0.1Co0.8Fe0.2O3-δ. The results identified SDC and GDC as good matches with (Ba0.5-Sr0.5)0.9Ca0.1Co0.8Fe0.2O3-δ as there was still no secondary phase when they were heat treated at 900ºC. Using 4-point probe method to measure the conductivity found that the highest conductivity was 59 Scm-1 at 600 ºC. Compared to the cathode material Ba0.5Sr0.5Co0.8Fe0.2O3-δ with no calcium doping, the electrical properties reported significant improvement. The thermal expansion coefficient of the calcium-doped cathode read 17.29 x 10-6 K-1 when heat treated at 800 ºC, showing an obvious decrease as compared to the thermal expansion coefficient of the undopped BSCF (19.7 × 10-6 K-1). As the above experiment results demonstrate, BSCaCF emerges as a more promising new SOFC cathode material than the traditional BSCF.