釩摻雜鈰酸鑭作為陽極材料與用兩階段燒結合成LSGM電解質材料應用於中溫型固態氧化物燃料電池之研究

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，並探討金屬離子摻雜對材料物理及電化學性質之影響，而另外成功以兩步驟燒結的方式成功合成鎵離子取代A位且鎂離子取代B位之LaGaO3化合物。 對於La2(Ce1-yVy)2O7-系列，在0 ≤ y ≤ 0.2可以合成出純相化合物，並透過元素組成的分析作證實。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 ºC會開始與氫氣反應，並且至900 ºC尚能維持結構穩定性。供電性測試使用而壓制成的碇材的最佳燒結條件為1500 ºC持溫一小時。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，於600 ºC -900 ºC，離子導電度為4.8×10-3 - 1.3×10-1 S/cm，其導電度略高於YSZ((Y2O3)x(ZrO2)1-x)。 對於LSGM(La0.8Sr0.2Ga0.8Mg0.2O3)材料，利用X光繞射儀、掃描式電子顯微鏡進行性質與結構的鑑定，本材料之碇材利用預先合成的粉體壓製而成，最佳燒結條件為1450 ºC之下持溫 2小時，使用交流阻抗分析譜量測半電池之離子導電度，在500 ºC -900 ºC，離子導電度為2.9×10-5 - 1.07×10-1 S/cm，此純相粉體將用於電解質上並製備成單電池並測量其性質。 利用刮刀塗布法製作LSGM(La0.8Sr0.2Ga0.8Mg0.2O3)薄層以減少電解質層的厚度，而可控制刮刀狹縫的高度來製造出厚度110~170 μm之電解質薄層，此薄層也為單一純相，而其離子導電度在800 ºC及900 ºC分別為8.07×10-3 S/cm 和7.32×10-3 S/cm，因此可利用此電解質薄層進行中溫型固態氧化物之研究，分別將本實驗以溶膠-凝膠法(sol-gel method)合成之La2(Ce0.8V0.2)2O7-作為陽極、LSM20-I ((La0.80Sr0.20)0.95MnO3-x) 作為陰極，搭配上先前合成之LSGM薄層，LSGM在此單電池中提供了良好的電化學表現，而此單電池在不同溫度下之功率密度分為115, 109 and 98 mW/cm2 at 900, 850 and 800°C。此結果顯示以LSGM薄層當作電解質支撐之固態氧化物燃料電池可在800 °C左右也具有充足的性能表現。

In this thesis, series of La2(Ce1-yVy)2O7- were prepared by sol-gel method to study the influence of metal cation to their physical and electrochemical properties, for La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM) was successfully synthesized by 2-step sol-gel method. For La2(Ce1-yVy)2O7- series, pure phase were observed in a range of 0 ≤ y ≤ 0.2 and their compositions were analyzed by ICP-AES/SEM-EDS. The refined cell constants decreased as V contents increased. From the TPR result, these materials started to react with hydrogen in the temperature range of 400-750 ºC and they exhibited structural stability up to 900 ºC. The dense ceramic pellets were sintered at 1500 ºC under air for 1h. Total ionic conductivity increases with the substituted-V content. La2(Ce0.8V0.2)2O7- exhibited high total ionic conductivity of in the range of 4.8×10-3 - 1.3×10-1 S/cm at 600-900 ºC, which is higher than the total ionic conductivity of YSZ((Y2O3)x(ZrO2)1-x). For LSGM(La0.8Sr0.2Ga0.8Mg0.2O3) materials, these were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM). The dense ceramic pellets were sintered at 1450ºC under air for 2h by as-prepared powders. For LSGM, the measurement of ionic conductivity via EIS showed that the conductivities were in a range of 2.90×10-5 – 1.07×10-1 S/cm at 500-900 °C. The pure material will be used in single cell fabrication and analyze the power performance of the cells. A La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) thin film was fabricated by the usual tape casting method using a doctor blade to reduce the operating temperature in solid oxide fuel cells (SOFCs). The resultant LSGM film was 110~170 μm in thickness by control the gap of doctor blade. Also, the thin LSGM film showed a single phase, and its conductivity was 8.07×10-3 S/cm at 900 °C and 7.32×10-3 S/cm at 800 °C, respectively. Therefore, it seemed that the thin LSGM film was suitable as an electrolyte for intermediate temperature operating SOFCs. La2(Ce0.8V0.2)2O7- synthesized by sol-gel method was used as an anode and LSM20-I ((La0.80Sr0.20)0.95MnO3-x) was used as a cathode, respectively, and a single cell was fabricated with the thin LSGM film as an electrolyte. This single cell with the thin LSGM electrolyte exhibited excellent electrical performance, of which power density was over 115, 109 and 98 mW/cm2 at 900, 850 and 800°C, respectively. These results suggested that the LSGM-based SOFCs with the thin LSGM film in this study would exhibit adequate performance at a temperature lower than 700 °C.