固態氧化物燃料電池Ba0.25Sr0.45 La0.3Co0.8Fe0.2O3-δ陰極材料之製備及性質研究

本論文之目的為降低中溫型固態氧化物電池陰極材料與電解質極化現象。比較La0.6Sr0.4Co0.8Fe0.2O3-δ(LSCF)及Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF)混合而成Ba0.25Sr0.45La0.3Co0.8Fe0.2O3-δ (BSLCF)與直接合成(S-BSLCF) 性質之差異。在燒結1000 oC形成單一相BSLCF鈣鈦礦結構，隨著燒結溫度上升晶粒逐漸成長。BSLCF之熱膨脹和熱重量損失有明顯轉折點，歸咎為氧空位產生和價數的還原。BSLCF 1100 重量損失為2.78%最大，表示氧空位產生最多，而BSLCF熱膨脹係數在25.75~29.86(×10-6 K-1)，隨著產生氧空位越多熱膨脹係數越大。BSLCF不同燒結溫度有不同的導電行為，其中BSLCF1100導電率為1584 S/cm最大，類似金屬導電行為，而BSLCF1000為P型半導體行為。在交流阻抗分析中，BSLCF1100在600 oC面積比阻抗明顯小於BSCF和LSCF，而價數轉換阻抗值為0.19Ω•cm2及氣體擴散阻抗為0.57Ω•cm2。接下來針對BSLCF 1100 oC在不同燒結時間與S-BSLCF作比較。BSLCF與S-BSLCF皆能得到單一相鈣鈦礦結構，晶格常數相近均3.865±0.002Å，經由ICP-MS得知BSLCF各元素莫耳數與S-BSLCF一樣且A/B比例為1。BSLCF表面型態隨燒結時間增加晶粒成長越明顯但孔隙率也逐漸減少，BSLCF孔隙率則比S-BSLCF還要高。BSLCF之熱重量損失 (1.76~2.78%)明顯大於S-BSLCF值為(1.67%)，且熱重損失經循環測試中重量並沒有改變，表示晶格中氧能隨著周圍環境達到平衡。BSLCF熱膨脹係數為23.71~29.86(×10-6 K-1)，其中BSLCF燒結2小時與S-BSLCF值(23.58×10-6 K-1)相近。BSLCF之導電率明顯大於S-BSLCF值(950 S/cm)，其中BSLCF燒結16小時導電率為最高。其中BSLCF燒結2小時與S-BSLCF呈現P型導電機制，而其餘BSLCF為金屬型導電機制主要受到電荷濃度影響。交流阻抗分析中，BSLCF經5、9及 16小時燒結於600 oC擴散換阻抗值分別為0.64、0.57及0.69 Ω•cm2 都明顯小於S-BSLCF之2.13 Ω•cm2，且整體阻抗值BSLCF明顯小於S-BSLCF。

關鍵字

固態氧化物燃料電池；陰極；電子導性；交流阻抗

並列摘要

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.

並列關鍵字

Solid oxidefuelcells ； Cathode ； Electrical properties ； Impedance

參考文獻

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固態氧化物燃料電池Ba0.25Sr0.45 La0.3Co0.8Fe0.2O3-δ陰極材料之製備及性質研究

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