鉍錳鐵摻雜氧化鈰材料用於中溫固態燃料電池電解質之研究

Abstract

本研究探討鉍、錳、鐵共摻雜氧化鈰之電解質材料之合成、燒結行為、電性劣化與應用於中溫固態燃料電池電解質之電能輸出表現。以EDTA-檸檬酸法合成特定摻雜量的粉末，利用熱膨脹儀(DIL)和密度量測研究燒結行為，以X光繞射法(XRD)分析結晶相，以及數種電子顯微鏡觀察微結構。先前(邱傑)的研究報導鉍的固溶限為8-9 at%，錳、鐵的固溶限少於1 at%。鉍錳鐵共摻雜氧化鈰(Ce0.9(Bi0.09Mn0.5Fe0.5)O2，簡稱 9HH)可以在1050°C持溫1小時燒結緻密，其熱膨脹係數約為15.5x10-6 K-1，和陰極材料鑭鍶鈷鐵(LSCF-6428)匹配。在650°C長時間的電性穩定性測試，顯示鉍摻雜氧化鈰的材料可以透過添加微量的錳、鐵明顯的提升高溫導電性，而劣化主要原因來自於第二相r相氧化鉍的生成與氧空位的聚集。最後，五層結構的單電池之結構中含緻密8YSZ(3.1 μm)/9HH(2.2 μm)雙層電解質，改善後之電池在800°C之輸出為242 mW.cm-2。

The effects of bismuth, manganese and iron co-doping in ceria-based materials used as electrolyte of solid oxide fuel cells have been investigated in this study. The powders are synthesized by EDTA-citric acid method. The sintering behavior is analyzed by dilatometry (DIL) and density measurement. X-ray Diffraction (XRD) is used to identify crystalline phases. Microstructure of the samples is observed by various electron microscopies. Previous work (by J. Chiu) reported that the solubility limit of Mn and Fe in ceria is less than 1 at% while that of Bi is at 8-9 at% in the presence of Mn and Fe. Ce0.9(Bi0.09Mn0.5Fe0.5)O2 can be sintered dense only at 1050°C for 1 hr. Its coefficient of thermal expansion (CTE) is about 15.5x10-6 K-1 within 30-800°C, matches with CTE of LSCF-6428. Long-term stability of Bi-doped ceria can be improved by doping trace amount of Mn and Fe because the formation of second phase (r-Bi2O3) and vacancy ordering would be suppressed even annealing at 650oC for 100 hr. Finally, the anode-supported cells of 5 layers are assembled and improved. The improved cell containing 8YSZ (3.1 μm)/9HH (2.2 μm) bilayer electrolyte shows a maximum power output of 242 mW.cm-2 at 800°C.