以氧化鋯複合氧化鈰電解質中溫固態氧化物燃料電池之製備與性質研究

Abstract

本博士論文主要以GDC摻雜鋯金屬當作複合式電解質，利用Pichini方法合成粉體材料，並測量其物理性質與電性表現，主要分為三個部分。第一部分是利用不同檸檬酸對總金屬離子的比例去合成粉體材料，依不同當量比命名為 1-GDC、1.5-GDC和2-GDC。利用XRD、SEM、TEM和TGA測量其物理性質，實驗結果發現用1.5倍當量檸檬酸對總金屬莫爾比合成粉體時，在140°C烘箱下有自燃現象的發生，經TEM儀器觀察下，1.5-GDC粉體比1-GDC和2-GDC有最小的顆粒大小與良好的分散性，將粉體壓成錠狀並燒瑕到1500°C測量其導電度，1.5-GDC比1-GDC和2-GDC在500-700°C測量下有較好的導電度，1.5-GDC電解質在700°C下其導電度可達到3.26 S/m。單電池的測試以60%NiO當作陽極，6428-LSCF當作陰極，用1.5-GDC當作電解質，氣體流速控制在100 ml/min氫氣，160 ml/min空氣，在650°C可測到最大功率為628 mW/cm2和較高的開路電壓。 第二部分以鋯離子部分取代電解質CGO中的鈰離子和鋯跟鈣離子共摻雜CGO中的鈰離子，材料化學式為Ce0.8-xGd0.2Zr0.1-xO2 (x-CGZrO)和Ce0.8-xGd0.2Zr0.1-xCayO2 (xy-CGZrCaO)。經XRD測量發現x-CGZrO和xy-CGZrCaO粉體在700°C瑕燒下其結構為螢石結構，並無任何雜相的生成，在TEM觀察下發現x-CGZrO和xy-CGZrCaO顆粒大小皆比R-GDC要來的小，導電度的測量發現，共摻雜系統中22CGZrCaO在700°C下有最好的導電值5.15 S/m，比單摻雜的3CGZrO還要好( 3.26 S/m )，製備單電池時，用x-CGZrO與xyCGZrMO當作電解質，3-CGZrO當作電解質有最大電功率725 mW/cm2，其歐姆阻抗值最低可到0.179 Ωcm2。接著第三部分是附合式陰極的研究，利用先前做到最好氧離子導電度的3-CGZrO、22CGZrMgO和22-CGZCaO去複合LSCF陰極，複合的重量比20 wt %，複合式陰極表示為20%-3CGZrO/LSCF、20%-22CGZrMgO/LSCF和20%-22CGZrCaO-LSCF。複合式陰極製備用物理混合法，並接著做成單電池，在650°C 下測量發現已20%-22CGZrCaO-LSCF 當作複合是陰極友最佳的電功率827 mW/cm2，且其電極阻抗值最小可達到0.128 Ωcm2，比LSCF當陰極製備的單電池還要來的好 ( PPD =628 mW/cm2 )。

In the first parts, Gd-doped CeO2 (abbreviated GDC) with the composition Ce0.8Gd0.2O2-d was synthesized by Pechini method using different amounts of citric acid as the chelating agent. The molar citric acid to total metal ion ratios (R values) were varied from 1, 1.5 to 2. It was noticed that citric acid could help self-ignition when the ratios were 1.5 and 2. The transmission electron microscopic images showed that 1.5-GDC prepared with R= 1.5 contained smaller and more homogeneously distributed particles than the other two samples (1-GDC and 2-GDC). As a result, the electrolyte pellet prepared by sintering 1.5-GDC powders at 1500°C exhibited higher relatively density than those made from 1-GDC and 2-GDC, and it gave higher oxide ion conductivity at 500-700°C. Anode-supported SOFC single cells were fabricated by a simple co-pressing method using 60%NiO/Ce0.8Gd0.2O2 as anode and 6428-LSCF as cathode. The single cell prepared with 1.5-GDC electrolyte also gave highest power density and open circuit voltage. In the second parts, the Gd-Zr co-doped and Gd-Zr-Ca co-doped ceria was investigated. Ce0.7Gd0.2Zr0.1-xO2 (x-CGZrO) and Ce0.8-x-yGd0.2ZrxCayO2 (xy-CGZrCaO) powders were synthesized by Pechini method. The XRD results showed that Gd-Zr and Gd-Zr-Ca co-doped ceria calcined at 700°C had fluorite structure and smaller particle sizes than pristine GDC. Among these co-doped ceria, 22CGZrCaO has the highest oxide ion conductivity (5.15 S/m at 700°C). Moreover, Ce0.76Gd0.2Zr0.02Ca0.02O2-d sintered at 1500°C exhibited higher oxide ionic conductivity (5.12 S/m 700°C) than Ce0.8Gd0.2O2-d sintered at 1500°C (3.26 S/m). The single cell prepared with 3CGZrO electrolyte gave highest power density (725 mWcm2) and lowest ohmic resistance (0.179 Ωcm2). In the third parts, the x-GDC/LSCF (x= 10-50%), 20%-3CGZrO, 20%- 22CGZrMgO/LSCF, and 20%-22CGZrCaO/LSCF composite cathodes are investigated for the potential cathode for IT-SOFCs. The optimal content of GDC in composite cathode was determined to 20 wt%, which could give the higher maximum power density (827 mWcm2) than pure LSCF cathodes (628 mWcm2) at 650°C. In addition, among these composite cathodes, 20%-22CGZrCaO/LSCF results in the lowest polarization resistance (0.128 Ωcm2) and highest single cell performance (827 mWcm2).