本研究主要利用穿透式電子顯微鏡、拉曼光譜儀、X光繞射分析儀、交流阻抗分析儀等，分析共摻雜氧化鈰電解質的微觀特性、氧空位分佈與離子導電之關聯性，以及複合纖維陰極的催化特性。
首先，氧化釓(Gd2O3)與氧化鍶(SrO)共摻雜含量對於兩種不同共摻雜氧化鈰系統(Ce0.8Gd0.2-xSrxO1.9-0.5x and Ce0.8-xGd0.2SrxO1.9-x)，對微觀、離子電導率與氧空缺含量的影響進行研究。X光繞射圖譜的結果顯示所有的試片呈現立方相的結構。共摻雜氧化鈰系統的晶格常數隨著摻雜含量提升而呈現線性上升，其歸因於鍶離子具有較大的離子半徑。於相同的氧化鍶摻雜量下，共摻雜氧化鈰系統Ce0.8-xGd0.2SrxO1.9-x的粒徑明顯大於另一個Ce0.8Gd0.2-xSrxO1.9-0.5x系統；根據氧空缺含量的計算，Ce0.8-xGd0.2SrxO1.9-x具有較多的氧空缺數量，有助於氧離子、缺陷或不純物的擴散。少量的氧化鍶添加於GDC電解質將有效於提升離子電導率，但是電性迅速下降出現於氧化鍶重度摻雜的條件下。有趣的是，在共摻雜氧化鈰系統中，非對稱的拉曼F2g峰和氧空缺相依的拉曼散射峰則出現於465 cm-1 和 566 cm-1附近的拉曼位移位置。二價與三價陽離子摻雜於氧化鈰會產生不同的氧空缺分佈，並且可以藉由拉曼光譜分析去分離其摻雜的貢獻。可發現隨著氧化鍶摻雜量增加，氧空缺拉曼散射峰566 cm-1強度降低；而氧化鈰主要的拉曼散射峰則朝向低頻位移。此表示，共摻雜系統氧空缺含量隨著Gd3+和Sr2+共摻雜濃度增加而提升，雖然於拉曼位移566 cm-1處的拉曼散射峰強度值，隨著Sr2+於GDC的數量增加而降低，且共摻雜GDC的離子電導率有明顯上升；但是若GDC主散射峰F2g非對稱性大幅降低，且半高寬明顯提升的時候，則會因為產生嚴重的晶格畸變而使離子電導率快速下降，此現象則出現在重度摻雜的時候。因此我們認為，拉曼光譜是分析區域細微結構與離子電導率關係的重要工具之一，並且藉由拉曼光譜散射峰的變化則可以預估共摻雜系統離子電導率的變化。詳細的討論內容與數據呈現則歸納於本文中。
其次，本論文利用靜電紡絲手法製作Ce0.78Gd0.2Sr0.02O2-δ(GSDC)微奈米纖維，並對製程參數進行系統性的研究，將陶瓷纖維製程最佳化。結果顯示，最佳製備條件為電壓20kV、polyvinyl pyrrolidone(PVP)濃度為整體溶液的11.32wt%，可得到直徑均勻150nm，表面平滑且連續的GSDC纖維。觀察傳統爐燒與微波燒結對於GSDC微奈米纖維微觀變化的影響。與傳統爐燒相比，在低溫微波燒結微奈米GSDC纖維就可以明顯達到成相的結晶性，將有利於離子的傳導，進而提升整體的電極性能表現。
複合80 wt% LSCF- 20 wt% GSDC (L8G2)纖維陰極的交換電流密度值明顯高於其它LSCF-GSDC的複合陰極。此外，快速的升溫速率與較少的燒結時間則有助於抑制嚴重的纖維成長與陰極緻密度。藉由微波燒結的複合纖維陰極L8G2材料系統，則呈現較低的極化電阻與較高的交換電流密度，其歸因於多孔結構提升三相點的範圍而增加氧氣的還原反應機率。總之，微波燒結的LSCF-GSDC複合纖維陰極在低的燒結溫度提供了提升催化特性的可能性。研究結果則證實，利用微波燒結製作靜電紡絲複合纖維陰極的新技術，提供更廉價與方便的方式製作複合陰極，能提升三相點催化氧氣之活性，並增加催化反應面積與速率，有助於提升SOFC之效能。

In this study, the relationship among microstructure features, oxygen vacancy distributions and ionic conductivities of Gd3+ and Sr2+ co-doped ceria electrolytes and catalytic properties the ceria-based fiber cathodes are investigated by using transmission electron microscopy (TEM), Raman Spectrometer, X-ray diffractometer and AC impedance analyzer.
First, effect of Gd2O3 and SrO co-dopants amount on microstructural features, ionic conductivities and oxygen vacancy concentrations of two modified ceria electrolytes (Ce0.8Gd0.2-xSrxO1.9-0.5x and Ce0.8-xGd0.2SrxO1.9-x) are studied. The XRD results reveal that all specimens are cubic structure. Lattice parameters of co-doped ceria were observed to linearity increase with an increase of co-dopants amount, due to large radius of Sr2+. Grain size of Ce0.8-xGd0.2SrxO1.9-x is significantly larger than that of Ce0.8Gd0.2-xSrxO1.9-0.5x at the same Sr2+ concentration, because Ce0.8-xGd0.2SrxO1.9-x possesses more oxygen vacancy to migrate oxygen ion, defects and impurities easily based upon calculation of oxygen vacancy amount. Small addition of SrO into 20 mol.% Gd2O3 doped ceria was effective in enhancing of ionic conductivity, but a sudden decreasing of conductivity with Sr2+ heavy-doping. It is interesting that asymmetry Raman bands of the F2g and vacancy modes appear in aliovalent cations co-doped ceria at around 465 cm-1 and 566 cm-1 respectively.
Different morphologies of oxygen vacancy distribution affected by di- and tri-valent cations in two co-doped ceria systems could be separated and analyzed from Raman spectra. An decrease of intensity of the observed Raman band at 566 cm-1 and the negative frequency shifts of the F2g mode intensity with increased doping is found, indicating that the oxygen vacancy amount increases as the Gd3+ and Sr2+ concentrations increase. The peak intensity of 566 cm-1 feature increased with decreasing of oxygen vacancy amount when addition of Sr2+ in GDC, and then ionic conductivity of co-doped ceria was enhanced. But, if the F2g peak becomes increasingly asymmetric and full width at half maximum of the F2g peak significantly increases with Sr2+ content due to formation of serious distortion of lattice in co-doped ceria. It is found rapid decrease of ionic conductivity in co-doped ceria. We propose that Raman scattering is a very useful analytical tool for the study of relationship between variations of ionic conductivity and localized find structure of co-doped ceria and to estimate the variation of ionic conductivity. The details for discussing the relationship between localized fine structure and ionic conductivity in co-doped ceria systems were also discussed in this work.
Second, the influence of electrospinning parameters including polymer and applied voltage on microstructural features of Ce0.78Gd0.2Sr0.02O2-δ (GSDC) nanofiber are also investigated. Cathode catalyst of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) particle mixed nano-GSDC electrolyte fiber is coated onto GSDC electrolyte to study its catalytic property. The experimental results that a uniform GSDC nano-fiber of 150 nm diameter could be spun at the concentration of polyvinyl pyrrolidone (PVP) approximately 11.32 wt.% and applied voltage of 20 kV. Variations of microstructures in nano GSDC fiber with conventional furnace and microwave sintering were studied as well. Compared to conventional furnace sintering, significant improvement in crystallinity and density of GSDC fiber at lower sintering temperatures with microwave sintering was observed.
The exchange current density of the 80 wt% LSCF- 20 wt% GSDC (L8G2) nano-fiber composite cathode is much better than that of other LSCF-GSDC fiber cathodes. In addition, rapid heating rate and short sintering time for restricting serious fiber growth and density of cathode were observed as well. LSCF-GSDC fiber cathodes sintered by microwave furnace demonstrate the lower polarization resistances and the higher exchange current values. It is due to increasing of three phase boundary by porous fiber structure to increment oxygen reduction reaction. According to these above results, we would like to emphasize that microwave sintered LSCF-GSDC fiber cathode at low sintering temperatures provides the ability to enhance catalytic properties. The experimental results in this study confirmed that the new technology including fabrication of electrospun nano-fiber cathode by microwave sintering proposed will provide a more convenient and cheap approach to the fabrication of the composite fiber cathode.

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