具鈣鈦礦結構之氧化物La1-xSrxCuO2.5-δ(0.15x0.25)，因具高電子導率(於800oC時約為800 S/cm)與氧空缺濃度(16.67%)，因此，本論文研究以具鈣鈦礦結構之鍶摻雜銅酸鑭(LSCu)做為中溫固態氧化物燃料電池(IT-SOFC)之陰極材料。首先，本文說明在不同鍶摻雜條件下，鑭銅氧化物的結構變化與其導電性特性，未添加鍶的情況下氧化鑭/氧化銅混合粉末於960oC大氣氣氛下煆燒後，形成具K2NiF4結構之La2CuO4與過量的CuO。當鍶摻雜量從0%增加到25%時，煆燒後之試樣從La2CuO4/CuO混合相變化至斜方相鈣鈦礦結構之La0.85Sr0.15CuO2.5-δ，再變化至正方相鈣鈦礦結構之La1-xSrxCuO2.5-δ (x =0.2與0.25)。根據LSCu之滴定結果與鍶摻雜之缺陷方程式分析鍶摻雜效應對鈣鈦礦結構穩定性的影響中，當鍶離子而佔據鑭離子晶格位置時，會形成帶有負電荷效應的SrLa'，為平衡材料的電中性，因而形成了帶正電效應缺陷—電洞，所形成的電洞會與二價銅離子結合成三銅離子，由於材料中三價銅離子濃度的增加，降低了銅離子平均離子半徑，同時增加銅離子與鄰近氧離子的鍵結強度，因而穩定了LSCu的鈣鈦礦結構。然而，當鍶的摻雜量高於約25%將會超出其溶解度極限，此時，隨著鍶的摻雜量增加，將會有雜相Cu2SrO3與La2SrCu2O6相繼出現。

　　接著進行LSCu的銅離子價態、膨脹係數、陰極過電壓行為、與釔安定氧化鋯(YSZ)反應時之高溫穩定性以及LSCu/YSZ界面電阻等試驗。當LSCu試樣從室溫加熱至800oC時，藉由其尺寸隨溫度增加的變化量，可計算出正方相具鈣鈦礦結構LSCu的熱膨脹係數約在1.6810-5 至1.7910-5 K-1之間。陰極材料LSCu與常用的電解質材料YSZ的高溫穩定性，則是利用LSCu/YSZ的混合粉末置於高溫爐中熱處理後分析，當LSCu/YSZ混合粉末於800oC空氣氣氛下共熱1000小時後並無反應物生成，然而當LSCu/YSZ混合粉於900oC以上熱處理時，將會有反應物SrZrO3與La2Zr2O7相繼生成，同時亦會有部分鈣鈦礦結構的LSCu相分解成La2CuO4與CuO。此外，藉由對LSCu/YSZ/Pt半電池LSCu/YSZ界面的陰極過電壓量測與交流阻抗分析，推斷LSCu中大量的氧空缺提供了電極表面的陰極反應位置，同時亦提供了氧離子擴散往空氣/電極/電解質三相點與電極/電解質界面的擴散途徑，因此，在LSCu/YSZ/Pt半電池測試中，當試樣在操作溫度為800oC並通入密度為200 mA/cm2的電流後，LSCu/YSZ界面具有良好的陰極過電壓行為(約為12 mV)與低極化電阻(約為0.25Ω)。

　　最後，本研究將多孔質LSCu被覆於具YSZ薄膜電解質的陽極支撐基板上，進行IT-SOFC單電池電力測試。當單電池操作溫度為800oC，陽極端與陰極端分別通入150與500 sccm的氫氣與空氣進行測試時，單電池的最大電力密度約為0.56 W/cm2。此外，進一步在LSCu陰極層與YSZ電解質層間加入一陰極/電解質中間層—緻密的釤安定氧化鈰(SDC)層，以避免單電池高溫製程中(850oC)，LSCu/YSZ界面產生微量的反應物，由於SDC的加入，單電池的最大電力密度增進至0.87 W/cm2。

　　根據本研究對LSCu結構與材料特性分析以及半電池與單電池測試結果，正方相具鈣鈦礦結構之鍶摻雜銅酸鑭極有潛力成為中溫固態氧化物燃料電池之新陰極材料。

ABSTRACT

　Oxygen-defifcent perovskite type oxides La1-xSrxCuO2.5-δ (LSCu) have been synthesized in the composition range of 0.15x0.25. Due to their high electrical conductivity (800 S/cm at 800oC) and high oxygen vacancy concentration (16.67%), these materials are characterized as new cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). First, the structural and electrical properties of lanthanum copper oxide were examined as a function of strontium addition. It was observed that the lanthanum oxide and copper oxide formed La2CuO4 with K2NiF4 structure and exceeds CuO when the powder mixture was calcined at 960oC in ambient pressure. As the strontium was doped from 0% to 25% , the calcined powder mixtures were phase transformation from La2CuO4/CuO mixture to orthorhombic perovskite La0.85Sr0.15CuO2.5-δ to tetragonal perovskite La1-xSrxCuO2.5-δ (x=0.2 and 0.25). Based on the titration analyses and pertinent defect reactions, the enhancement of perovskite stability is due to the presence of electron holes by strontium addition. As the strontium ions were added and occupied the lanthanum lattice sites, negative effective defects SrLa' were formed. The positive effective defects—electron holes were created and associated with divalent ions to form trivalent copper ions and balance the electrical charge by strontium doped. The formation of trivalent copper ions decrease the mean radius of the copper ions and increase the bonding strength of the copper ions toward their neighbor oxygen ions. Therefore, the perovskite structure of the LSCu was enhanced. When the Sr dopant exceeded its solubility limit of approximately 25% in the A-site sublattice, the Sr-rish second, La2SrCu2O6 and Cu2SrO3 appeared.

　Then the thermal expansion, cathodic overpotential, structural stability of LSCu against yittria-stabilized zirconia (YSZ) and the polarization resistance of the LSCu/YSZ interface were examined. The thermal expansion coefficients of LSCu, calculated by fitting the dilatometric curves, are in the range of 1.6810-5 to 1.7910-5 K-1 from 20 to 800oC. LSCu show no reaction against 8YSZ at 800oC for 1000 hours. However reaction between LSCu and YSZ occurred at 900oC. According to overpotential measurement and as impedance analyses, it can be suggested that the high oxygen vacancy concentration of LSCu provides numberous pathways for the diffusion of oxygen ions from electrode surface to air-electrode-electrolyte triple phase boundary and electrode/electrolyte interface. Hence, as the LSCu/YSZ/Pt half cell operating at 800oC and after passing a current of 200 mA/cm2 , it exhibits a good overpotential behavior of about 12.6 mV and a low polarization resistance of 0.25Ω at LSCu/YSZ interface.

　Lastly, the porous LSCu layers were applied on the anode-supported substrate with YSZ electrolyte thin film for the IT-SOFC single cell performance testing. The maximum power density of the cell operating at 800oC with 150 and 500 sccm of hydrogen and air flow, respectively, is about 0.65 W/cm2. For further improvement of the cell by applying a dense samaria-doped ceria (SDC) layer as cathode/electrode interlayer, the maximum power density of the cell was enhanced to 0.87 W/cm2. According to these results, LSCu is a potential new cathode material for IT-SOFC.

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