| Summary: | 碩士 === 元智大學 === 化學工程與材料科學學系 === 99 === The objective of this study was to decrease the polarization of cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). To compare the character of Ba0.25Sr0.45La0.3Co0.8Fe0.2O3-δ(BSLCF) synthesized by La0.6Sr0.4Co0.8Fe0.2O3-δ(LSCF) and Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) with direct synthesis of Ba0.25Sr0.45 La0.3Co0.8Fe0.2O3-δ(S-BSLCF). BSLCF has single-phase perovskite at sintered 1000 oC. The sizes of grain gradually increase, with sintering temperature increasing. The coefficient of thermal expansion and thermogravimetry of sample show turning point around 300~400oC, which is associated with the loss of lattice oxygen and reduction of transition metal valence. BSLCF 1100 showed the highest weight loss of 2.78% with more oxygen vacancies. The thermal expansion coefficients of BSLCF are in range of 25.78x10-6 to 29.86x10-6K-1 from 40 to1000 oC. The highest conductivity of BSLCF 1100 is 1584 S/cm which is belong to metal conductor behavior, but BSLCF 1000 is a p type semi-conductors behavior. Area specific impedance of BSLCF were obviously smaller than that of BSCF and LSCF sample, and the charge-transfer resistance and gas phase diffusion resistance of BSLCF 1100 are 0.19 Ωcm2 and 0.57 Ωcm2 at 600 oC, respectively.
BSLCF and S-BSLCF have single-phase perovskite structure with lattice parameter (a) of 3.865±0.002Å. ICP-MS showed moles of each element of BSLCF are similar with S-BSLCF and the A/B ratio is of 1. Morphologies of BSLCF displayed the growth of grain size with increasing sintering temperature, but the open porosity decreased. The weight loss of BSLCF obviously larger than that of S-BSLCF, the three heating-cooling cycles and the weight loss of the samples showed good reproducibility that indicates all samples captured and released oxygen depend on the temperature. The thermal expansion coefficients of BSLCF are in the range of 23.71x10-6 to 29.86x10-6K-1, and BSLCF sintering at 1100oC for 2h is similar with the that of S-BSLCF (23.58x10-6K-1). The conductivity of BSLCF are better than that of S-BSLCF, and the conductivity of BSLCF sintered at 1100oC for 16h has the highest value. The AC impedance revealed the best electrochemical performance for BSLCF. For example, BSLCF sintered at 5、9 and 16h yielded the gas phase diffusion resistance of 0.64, 0.57 and 0.69 Ωcm2, respectively, which was smaller than S-BSLCF of 2.13 Ωcm2 at 600 oC.
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