研究影響NiO-YSZ陽極性能在固態氧化物燃料電池的應用

Abstract

本篇論文研究的目標為決定最好的製程條件以Ni-YSZ為基底的陽極材料應用在固態氧化物燃料電池(SOFC)，研究內容包括粉體合成、電池組裝己及性能測試。首先，使用四種不同的化學方法來合成Ni-YSZ粉體，分別為GNP燃燒法、共沉澱法、凝膠-溶膠法和水熱法，之後再用XRD分析相的結構和組成，SEM分析微結構。用GNP法合成得到的粉體效果最好，具有蓬鬆的海綿狀結構，粉末顆粒大小分佈均勻，而且在用共壓法組裝電池時有很好的效果。然後再從改變NiO/YSZ的比例、陽極孔隙率、陽極厚度、電解質厚度、共壓時的壓力和陰極這些條件來製備出最佳化電池，並拿去做電化學測試測性能。最佳的電池為NiO/YSZ比例為60、陽極孔隙率10%、陽極厚度為900 μm、YSZ電解質厚度為20 μm、共壓壓力為10 MPa，在800 ℃通入氫氣的條件下。較高的NiO/YSZ比例會造成三相界面(TPB)降低，使電池性能下降。孔隙率太低也會使TPB降低，太高無法支撐陽極容易使電池結構損壞。陽極厚度太薄無法支撐電池在高溫下容易損壞，太厚則減少氣體傳送速率。電解質則越薄越好可以降低歐姆電阻。壓力則要適中，太低結構還未成型，太高會損壞電池結構。 更進一步在最佳電池塗上LSM陰極，目前功率密度最多為0.62 W/cm2測量溫度為800℃。

The objective of this thesis is to determine the optimized condition for Ni-YSZ (yttria stabilized zirconia) based anode materials in solid oxide fuel cell (SOFC) application, and the research includes powder synthesis, cell fabrication and performance test. Ni-YSZ powder is initially synthesized from four different chemical methods；GNP (Glycine-Nitrate Process) combustion, co-precipitation, sol-gel and hydrothermal techniques. The synthesized powder is characterized by X-ray diffractometer (XRD) to analyze the phase-composition and scanning electron microscope (SEM) to examine the microstructure. The GNP synthesized Ni-YSZ, which is considered as the finest powder with the most foam-like structure and homogeneous distribution, is further employed to fabricate anode-supported SOFC by co-pressing method. The molar ratio of NiO/YSZ, anodic porosity, anodic thickness, electrolyte thickness and co-pressing pressure have been systematically examined in this fabrication process and are optimized at 6/4, 10%, 900 μm, 20 μm and 10 MPa, respectively, as cells are tested in the pure H2 fuel at the temperature range of 600 – 800 oC. Higher and lower NiO/YSZ ratio causes less TPB (Three-Phase-Boundary) and electrical conductivity, respectively, and results the degradation of the performance. Similarly, the lower porosity and thinner anode leads to the loss of TPB as well. However, the higher porosity and thicker anode causes the fragility of the ceramic. In addition, the thicker Ni-YSZ also results another problem of H2 transportation in the anodic region. The thickness of electrolyte is directly related to the junction potential of the cell and the 20-m YSZ, the thinnest electrolyte can be fabricated in our process, shows the best performance. Finally, the optimized anode/electrolyte cermet has further screen printed with the excellent cathode of LSM (Lanthanum Strontium Manganite，La0.8Sr0.2MnO3). The optimized SOFC of Ni/YSZ/LSM reaches the maximum power density of 0.62 W/cm2 at 800 ℃.