新穎金屬摻雜燒綠石陽極材料於中溫型固態氧化物燃料電池之應用與研製過程最佳化

Abstract

本篇論文以溶膠-凝膠法(sol-gel method)分別合成釩離子取代在B位之La2Ce2O7化合物以及鉻離子取代在B位之La2Zr2O7化合物，並探討金屬離子摻雜對材料物理及電化學性質之影響。另一方面，我們也成功地以兩階段燒結的方式合成鍶離子取代A位且鎂離子取代B位之LaGaO3化合物。 對於La2(Zr1-xCrx)2O7-δ系列，在800 °C持溫5小時的燒結條件下，摻雜比例0 ≤ x ≤ 0.2可以合成出純相化合物，並透過元素組成的分析證實。晶格精算結果發現，材料的晶格常數隨著鉻離子取代量的增加而先減後增。從熱程控還原反應實驗得知，樣品在400-600 °C會與氫氣反應，且樣品氧化還原穩定性不佳。在樣品燒結1600 °C持溫5小時後，樣品會開始出現LaCrO3的雜相，可見其在高溫下的不穩定性。 對於La2(Ce1-yVy)2O7-δ系列，在1000 °C持溫3小時的燒結條件下，摻雜比例0 ≤ y ≤ 0.2可以合成出純相化合物，並透過元素組成的分析證實。晶格精算結果發現，材料的晶格常數隨著釩離子取代量增加而下降。從熱程控還原反應實驗得知，樣品在400-750 °C會開始與氫氣反應，並且在900 °C尚能維持結構穩定性。供電性測試使用的壓製錠材之最佳燒結條件為1500 °C持溫1小時。此系列化合物離子導電度隨著摻雜比例增加而上升，於y = 0.2時有最大值，在 600-900 °C為4.8×10-3-1.4×10-1 S/cm，其導電度略高於YSZ((Y2O3)x(ZrO2)1-x)在相同溫度區間的導電度。 對於LSGM(La0.8Sr0.2Ga0.8Mg0.2O3-δ)材料，我們分別進行商業化LSGM粉體和自製LSGM粉體刮刀塗佈法製作電解質片，並使用X光繞射儀、掃描式電子顯微鏡暨能量散佈分析進行結構分析。交流阻抗分析圖譜量測半電池之離子導電度結果顯示，在600-900 °C下，商業化電解質片之離子導電度為7.77×10-4- 1.08×10-1 S/cm，而自製LSGM電解質片離子導電度為7.71×10-4-4.98×10-2 S/cm，歸因於緻密程度的差異。最後，我們製作La2(Ce0.8V0.2)2O7-δ/商業化LSGM/(La0.60Sr0.40)0.95Co0.20Fe0.80O3-δ(LSCF)鈕扣型單電池片，在850 °C有最佳功率密度0.336 W/cm2;而La2(Ce0.8V0.2)2O7-δ/商業化LSGM/LSCF-LSGM鈕扣型單電池片之24小時800 °C定電壓測試中，功率密度從0.151 W/cm2下降至 0.096 W/cm2。此外，在5 cm×5 cm大面積電池片的測試中，在800 °C下功率密度僅僅只有3.5 mW/cm2，且陰極電阻大，測試後試樣破裂。由實驗結果得知，商業化大面積電池片的目標仍有待努力，但La2(Ce0.8V0.2)2O7-δ的確在中溫型固態氧化物燃料電池之陽極材料上有應用的潛力。

In this thesis, a series of La2(Zr1-xCrx)2O7-δ and La2(Ce1-yVy)2O7-δ were synthesized by sol-gel method to study the influence of metal cation to their physical and electrochemical properties. The electrolyte material, La0.8Sr0.2Ga0.8Mg0.2O3-δ(LSGM) was successfully synthesized by two step sintering method. For La2(Zr1-xCrx)2O7-δ series, pure phases in a range of 0 ≤ x ≤ 0.2 were observed from sintering stoichiometric amount of precursors at 800 °C for 5 hours. The as-prepared products were analyzed by ICP-AES/SEM-EDS for chemical composition. According to the refined unit cell from powder X-ray diffraction patterns, the refined unit cell dimensios firstly decreased, and then increased as Cr contents increased. The TPR experiments indicated that the Cr-substituted materials started to react with hydrogen in the temperature range of 400-600 °C, and exhibited poor redox stability. After sintering at 1600 °C for 5 hours, the impurity phase LaCrO3 started to appear, indicative of stuctural instability at high temperature. For La2(Ce1-yVy)2O7-δ series, pure phases in a range of 0 ≤ y ≤ 0.2 were observed by sintering the precursors at 1000 °C for 3 hours, and their compositions were analyzed by ICP-AES/SEM-EDS. The refined unit cell constants from powder X-ray diffraction patterns decreased as vanadium composition increased. From TPR expriments, these materials started to react with hydrogen in the temperature range of 400-750 °C, and remained the structure up to 900 °C. The passed ceramic pellets were sintered at 1500 °C under air for 1 hour. Total ionic conductivity increased with increased vanadium substitutions. La2(Ce0.8V0.2)2O7-δ exhibited high total ionic conductivity in the range of 4.8×10-3-1.4×10-1 S/cm among the metal-substituted compounds, which is higher than the total ionic conductivity of YSZ((Y2O3)x(ZrO2)1-x). For LSGM(La0.8Sr0.2Ga0.8Mg0.2O3-δ) materials, we fabricated commercial LSGM and lab-prepared LSGM thin films by tape casting method. The unit cell dimensions and compositions were characterized by powder X-ray diffraction(PXRD) and SEM-EDS. For commercial LSGM and lab-made LSGM thin films, the measurements of ionic conductivity via EIS showed that the conductivities were in a range of 7.77×10-4-1.08×10-1 S/cm and 7.71×10-4-4.98×10-2 S/cm respectively. The reduced conductivities were attributed to the degree of dense for LSGM plate. We fabricated the single cell of La2(Ce0.8V0.2)2O7-δ/commercial LSGM/LSCF, which showed best power density of 0.336 W/cm2 at 850 °C. The 24 hours performance test for La2(Ce0.8V0.2)2O7-δ/ commercial LSGM thin film/LSCF-LSGM showed power density decreased from 0.151 W/cm2 to 0.096 W/cm2. Large single cell of 5 cm×5 cm(single cell of La2(Ce0.8V0.2)2O7-δ/commercial LSGM thin film/LSCF-LSGM) was fabricated. The as-prepared large single cell showed poor power density of only 3.5 mW/cm2 at 800 °C, due to the big cathode polarization resistance, and the single cell was broken during the cell performance test. There are still a lot of efforts to do to reach the goal of optimized performance. The pyrochlore phase La2(Ce0.8V0.2)2O7-δ is anticipated to be a potential anode material for intermediate temperature solid oxide fuel cell.