由於較高的工作溫度（800~1000oC），易衍生相變、熱應力、腐蝕、高運行成本等問題，是高溫燃料電池商業化的挑戰之一。近年來，為了降低高溫燃料電池工作溫度，可操作在500-650oC範圍之釤摻雜氧化鈰(Sm0.2Ce0.8O1.9; SDC)/鋰-鈉碳酸鹽(Li0.52Na0.48)2CO3; LNC)複合電解質呈現相當良好的離子導電率和獨特的混合離子傳導行為。但至於多重離子是如何傳導、個別離子的貢獻程度，以及 SDC /碳酸鹽之間界面之貢獻，都仍需要進一步釐清。
因此本研究之研究目的，是利用固相反應法分別合成SDC、 LNC電解質粉體，再藉凝膠冷凍乾燥法製作多孔SDC電解質基材。然後，將熔融的鋰/鈉碳酸鹽滲入而形成SDC/LNC複合電解質。之後，利用高解析SEM、XRD和電化學阻抗譜（EIS）進行複合電解質之微結構、結構和阻抗分析，以深入了解複合電解質在提升離子傳導之重要貢獻。
為了進一步檢視SDC/LNC複材系統的多離子傳導在燃料電池，以SDC/LNC複合電解質組裝成單電池，於650°C且H2/O2(air)氣氛下，於獲得340mW/cm2之功率密度。以傳統MCFC的LiAlO2/LNC電解質作為對照組，相較於LiAlO2/LNC電解質的電池154mW/cm2，達兩倍以上之性能表現。SDC/LNC複合電解質所以能有此一性能提升，除了因MCFC中使用惰性之LiAlO2基材被具有良好氧離子導性之SDC基材所取代外，SDC/LNC固-液界面之貢獻也不容忽視。本研究，在固定孔隙率（53vol%）條件下，製備不同孔洞尺寸（5,10,20μm）的多孔基材，以呈現不同固-液界面面積之效應。結果發現，當結構基材的孔洞從20μm改變為5μm時，在650oC下的電功率密度由126mW/cm2提升為340mW/cm2。此一性能提升推測為具5μm孔洞之複合電解質提供有助於離子傳導之龐大界面面積。由高解析穿透式電子顯微鏡之傅立葉轉換分析(Fast Fourier transform (FFT) analysis of the HRTEM)，發現由於陽離子在界面交互擴散確實造成SDC表面晶格扭曲，提供離子快速遷移之通道。因此，SDC/LNC複合電解質之界面是有助於其電化學性能之提升。

Since their high operating temperature (800~1000oC) tends to cause phase transition, thermal degradation, corrosion, high running cost, high temperature fuel cells still remain a number of challenges for commercialization. In recent years, samaria-doped ceria (Sm0.2Ce0.8O1.9; SDC)/((Li0.52Na0.48)2CO3; LNC) composite electrolytes have been developed for fuel cells to be operated at intermediate temperatures (500-650oC). This composite system exhibits impressive ionic conductivity and unique hybrid ionic conduction behavior. However, there are questions for such a composite still remain unclear with regard to the condcution mechanism of multi-ions and contribution of individual ions, especially the interface between SDC and LNC.
Therefore, the main objective of this study is to fabricate a novel composite using carbonate infiltration into a porous SDC framework otained from a gelation-freeze drying process. This composite were characterizd by High-resolution SEM, XRD, and Electrochemical Impedance Spectroscopy for microstructural, structural and impedance analyses to understand the important contribution of the composite electrolyte in improving ion conduction..
To further understand the advantage of multi-ion conduction, a single cell assembled using SDC/LNC composite was tested using H2/O2(air) at 650°C. The power density obtained was 340mW/cm2 which is two times as high as that from a conventional MCFC using LiAlO2/LNC electrolyte (154mW/cm2). In comparison to a conventional MCFC using LiAlO2/LNC electrolyte, higher power density of SDC/LNC cell may be attributed to the oxygen conduction from SDC. In addition, the contribution from SDC/LNC interface was examined based on various porous SDC framework with a fixed porosity of 53%. Composite electrolytes were fabricated using porous SDC frameworks with various pore sizes 5, 10, and 20μm. The power density measured from the cell based on a 20μm-pore SDC framework was 126mW/cm2 at 650oC. On the contrary, the power density measured was 340mW/cm2 from the cell based on a 5μm-pore SDC framework. Such enhancement in power density may be attributed to the enlarged interface area from the 5μm-pore SDC framework. From the Fast Fourier transform (FFT) analysis of the HRTEM, it was observed that cation inter-diffusion across the interface causes lattice deformation on SDC surface. The deformed lattice provides the path for ions to transport. As a result, the enlarged interface in SDC/LNC composite electrolyte may promote the ion migration and further enhance the desired electrochemical conversion in fuel cells.

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