固態氧化物燃料電池(Ba0.5Sr0.5)1-yMyCo1-xNxO3-δ(M=La, N=Fe, Cu)陰極材料之製備及性質研究

Preparation and Characterization of (Ba0.5Sr0.5)1-yMyCo1-xNxO3-δ (M=La, N=Fe, Cu) Cathode Material for Solid Oxide Fuel Cell

梁宸毓(Chen-Yu Liang)

指導教授 ： 洪逸明

元智大學/工程學院/化學工程與材料科學學系/碩士(2009年)

https://doi.org/10.6838/YZU.2009.00168

摘要

本實驗以Ba0.5Sr0.5CoO3(BSC)結構為主體，以低價Cu離子取代BSC中部分四價Co離子晶格位置(B-site)，利用電荷補償效應形成氧空缺來平衡電荷，增加氧空缺濃度及氧離子導性使陰極催化的電化學特性增加；並同時以三價且半徑較大之La離子取代BSC中部分A-site晶格位置，預期會增加其電子導性。藉由同時摻雜A-site和B-site離子來達到提升電子及氧離子導性和改善陰極的極化現象等目的。
實驗採用固相反應法、Pechini法及Citrate-EDTA合成法。發現使用Citrate-EDTA合成法所製備之Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF)粉末在形成BaCoO2.23之所需煆燒溫度、晶粒大小差異性、孔洞分佈及導電性質均較其他二種製程所合成之粉末佳。而後探討Citrate-EDTA合成法所製備粉末之前趨液pH值對於陰極材料之影響，發現使用不同pH值所製備的粉末皆具有相似的結構、晶格常數、微結構等，其結果顯示不同pH值對於BSCF粉末的結晶化跟結構影響不大。但使用pH=6所製備的粉末同時具有較好的化學計量比及電化學性質，其在400℃有最高的導電性50.2 S/cm，約比pH=9在400℃的導電率37.7 S/cm高出了33%。不同pH值所製備之BSCF皆具有相似的活化能，表示傳導機制相同。
決定製程條件後即進行利用Cu取代量為實驗變因之(Ba0.5Sr0.5)0.8La0.2Co1-xCux (BSLCCu)的陰極改質，發現在Cu為低取代量(≦0.2)時，經950℃的煆燒溫度後仍有第二相的生成，無法產生單一相的鈣鈦礦結構，但若經1050℃燒結後皆可得到單一相的鈣鈦礦結構。而所製備的BSLCCu之晶粒大小在x=0~0.15時約介於1~5μm，在x=0.2以上則明顯成長至10μm以上；且BSLCCu皆為多孔性的材料，其孔隙度大小介於1.44%~19.66%。另外觀察到當x值在0.3以上時在晶界會出現液相燒結的現象，而液相燒結會導致燒結體表面之孔隙度明顯減少。熱膨脹係數隨著Cu取代量的增加而減少，其熱膨脹係數介於15.8×10-6~24.8×10-6 K-1。導電率隨著Cu取代量的增加持續下降，且BSLCCu0.00在300℃達最高導電率689 S/cm，而最低之導電率為BSLCCu0.45在400℃之導電率221 S/cm。在低溫環境下之活化能Ea1值介於9.02 ~ 13.18 (kJ/mole)，在低溫環境下，改變Cu的取代量皆有相似的活化能，表示具有相似的傳導機制；而在高溫環境下之活化能Ea2，可發現隨著Cu取代量的增加，其Arrhenius曲線有趨於水平的現象，可推論在高溫環境中離子的活化能降低，使得氧離子較容易在晶格中擴散。交流阻抗分析可發現Cu的取代造成陰極擴散阻抗明顯的改善，而擴散阻抗又是陰極阻抗的主要來源，故可以得到隨著Cu的取代，可以改善陰極的極化現象並增加離子導性。

關鍵字

固態氧化物燃料電池 ； 陰極

並列摘要

The objective of this study was to promote ion and electronic conductivity and decrease the polarization of cathodes with Ba0.5Sr0.5CoO3-based cathode material. Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) were prepared by solid-state reaction methode, Pechini process and citrate-EDTA complexing method. From the results of XRD and conductivity, it was formed that BSCF prepared by citrate-EDTA complexing method have the best electrochemistry property.
Although the samples prepared from different pH solution have similar structure and microstructure morphologies. The optimized composition of BSCF electrode was prepared from the precursor solution with a pH value of 6 and showed highest conductivity of 50.2 S/cm at 400℃, which is 1.3 times higher than the sample prepared from the precursor solution with a pH value of 9.
The (Ba0.5Sr0.5)La0.2Co1-xCuxO3-δ (x=0~0.45, BSLCCu) were prepared with pH values of 6 by citrate-EDTA complexing method. X-ray diffraction results of all samples sintered at 1050℃ revealed that the single phase cubic structure of perovskite was formed. The grain size of BSLCCu (X=0~0.15) is in the range of 1~5 μm, and the grain size grow up to about 10μm as x≧0.2. The open porosity of BSLCCu was decrease with increase of x value. Coefficient(CTE) of thermal expansion (CTE) and conductivity of BSLCCu was also decrease with increase of x value. BSLCCu with x=0 showed the highest conductivity of 689 S/cm at 300℃, which is 3.1 times higher than that of BSLCCu with x=0.45. From the result of AC impedance, it was formed that the gas diffuses resistance of BSLCCu much lower than that of BSLC.

並列關鍵字

Solid Oxide Fuel Cell ； SOFC ； cathode ； BSCF

參考文獻

1. T. Horita, K. Yamaji, M. Ishikawa, N. Sakai, H. Yokokawa, T. Kawada, and T. Kato, "Active sites imaging for oxygen reduction at the La0.9Sr0.1MnO3-x/yttria-stabilized zirconia interface by secondary-ion mass spectrometry," Journal of the Electrochemical Society, vol. 145, pp. 3196-3202, 1998.

2. J. Mizusaki, Y. Yonemura, H. Kamata, K. Ohyama, N. Mori, H. Takai, H. Tagawa, M. Dokiya, K. Naraya, T. Sasamoto, H. Inaba, and T. Hashimoto, "Electronic conductivity, Seebeck coefficient, defect and electronic structure of nonstoichiometric La1-xSrxMnO3," Solid State Ionics, vol. 132, pp. 167-180, 2000.

3. Z. P. Shao and S. M. Haile, "A high-performance cathode for the next generation of solid-oxide fuel cells," Nature, vol. 431, pp. 170-173, 2004.

4. W. Grove, "On Voltaic Series and the Combination of Gases by Platinum," Philosophical Magazine and Journal of Science, vol. 14, pp. 127-127, 1839.

5. N.M. Sammes, R.J. Boersma, and G.A. Tompsett, "Micro-SOFC system using butane fuel," Solid State Ionics, pp. 487-491, 2000.