Preparation and Characterization of YxBa2-xCo2O5+δ Cathode Material for Solid Oxide Fuel Cell
| Autor: | Jeng-An Wang, 王政安 |
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| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 103 The double perovskite structure of YBaCo2O5+δ is different to typical perovskite cathode material, it has not only has excellent conductivity but also high concentration of oxygen vacancies. Therefore, it can decrease the polarization of cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The double perovskite structure of YxBa2-xCo2O5+δ (YBCO) has excellent conductivity and high concentration of oxygen vacancies, which is a potential cathode material of intermediate temperature solid oxide fuel cell. In this study, the YBCO powders were prepared using solid state reaction from various x values. The values of x is 1.2, 1.1, 1, 0.9 and 0.8. The conductivity and oxygen vacancies of YBCO increases by altering valance of A-site in this cathode material. This study showed that a single phase double perovskite Y1Ba1Co2O5+δ is prepared. The second phases of Y2O3, Y0.98(CoO3) and YBa2Co3O9-δ were observed as the x > 1 and x < 1, respectively. The lattice volume increases first and then decreases with the increasing contents of Y. The result of conductivity, the conductivity of YBCOs increase with the contents of Y increases. But the conductivity of YBCOs decrease due to the high amount of oxygen vacancies as the doping amount of Y increases. It exhibits a maximum conductivity of 450 S/cm at 350 oC in x = 1.0. In the thermal expansion result, doped Y reduces the CTE value of YBCO material and the value is 12.9 #westeur024# 10-6 / K as x = 1.2. It also shows a turning point at 350 oC in the results of conductivity, CTE and TGA and that due to the formation of oxygen vacancies. In composite cathode materials test, YxBa2-xCo2O5+δ(0.8≦x≦1.2) - Sm0.2Ce0.8O2-δ composite materials showed a good chemical composition at 950 oC. From the cross-sectional micrographs of symmetric cell, the microstructure showed a good adhesion between cathode and electrolyte layer, and the porosity of cathode layer is 25 %. The result of conductivity, the conductivity of YBCOs decrease by SDC mixed, and it exhibits a maximum conductivity of 64 S/cm at 300 oC in x = 1.0. In the thermal expansion result, mixed SDC success to reduce the CTE value and the value is 11.0 ~ 12.6 x 10-6 K-1. Comparing with YBCOs, the composite materials had better matching CTE with SDC. In the typical impedance spectra, the polarization resistance increase at initial and then decrease. It had a lowest value of 0.053 Ω cm2. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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