| 摘要: | 本研究使用已建立之高溫高壓雙腔體固態氧化物燃料電池(SOFC)實驗平台，搭配自製鈕扣型(小面積)和平板型(大面積)全電池測試載具，針對以氨為燃料，量測氨陽極支撐型全電池(Anode-Supported Cell, ASC)之電池性能曲線及其電化學阻抗頻譜，並探討其溫度、流率、壓力效應和不同反應面積之影響，也與氫燃料之結果作比較。本論文含四個部分：(1)比較ASC兩種不同陰極材料(i.e. lanthanum strontium cobaltite, LSC; lanthanum strontium cobaltite ferrite, LSCF)之電池性能與電化學阻抗頻譜；(2)氨ASC(Ni-YSZ/YSZ/LSC) 之壓力效應(1、3atm)和其穩定性測試分析；(3)氨ASC( Ni-YSZ/YSZ/LSC)於三個不同溫度600、650、700°C條件下，探討流率效應對電池性能之影響；(4)比較大面積(16 cm2)和小面積(1.54 cm2)之ASC的壓力效應對電池性能之影響。由第一與第二部分之結果顯示，當溫度為750~850°C時，使用氨燃料之電池性能幾乎與氫燃料相近，因氨氣在溫度於750°C以上時會裂解成氫氣與氮氣，隨後氫和氧反應成水。無論是使用氫氣或是氨氣燃料，提升溫度和壓力均可提升電池性能，兩者皆可使總極化阻抗減小，而歐姆阻抗則與加壓效應無關，但歐姆阻抗會隨溫度增加而下降。LSC材料因其電子導電率較LSCF材料高，故其電池性能較佳。於氨ASC之穩定性量測方面，在固定溫度750°C 、定電壓0.8V和1、3atm下，進行90分鐘穩定性測試，結果顯示氨ASC在穩定性測試期間並無電池劣化發生，且性能還略為提升1-3%，顯示氨SOFC在溫度750°C或以上具有良好的性能和使用壽命。
第三部份結果顯示，在溫度為600°C下，提升氨氣的流率並不能有效提升電池性能，因氨氣流率提升會降低其滯留時間，而氨氣裂解率會隨滯留時間減少而下降，導致陽極端的氫氣濃度降低。在流率提升的同時也會提升極化阻抗，因未參與反應的氮氣和生成物的增加影響了氣體的擴散所致。有關第四部分結果，從電化學阻抗來看，小面積電池片主要是由氣體擴散(特徵頻率10~100Hz)所主導，而大面積電池片主要是由氣體轉移(特徵頻率< 1Hz)所主導。這是因為大面積電池片燃料的消耗速率較快，因此出口燃氣少，產物多使氣體轉移阻抗增加。經加壓後，兩者總極化阻抗皆有所減少，表示加壓有助於提升電池性能。本研究成果對於未來開發氨SOFC為主的發電系統應有所助益。
;This thesis applies an already-established high-pressure and high temperature SOFC testing platform using a button cell (smaller reactive area; 1.54cm2) and a planar cell (large reactive area; 16cm2) to measure the cell performance and electrochemical impedance spectroscopy of anode-supported cell (ASC) fueled with ammonia. We investigate the impact of the temperature (T), the flow rate and the pressure (p) on the cell performance of different cells with different reactive area. Then we compare the results of both ammonia and hydrogen SOFCs. This study includes four parts. First, we compare the cell performance and electrochemical impedance spectroscopy of two ASC which has different cathode materials (i.e. lanthanum strontium cobaltite, LSC; lanthanum strontium cobaltite ferrite, LSCF). The second part is to measure the pressurization effect and the stability test of ASC (Ni-YSZ/YSZ/LSC) using by ammonia as a fuel. The third part is to investigate the flow rate effect of cell performance of ASC (Ni-YSZ/YSZ/LSC) fueled by ammonia at three different temperatures (600、650、700 oC). The fourth part is to compare the pressurized effect of ASC which has different reactive area. For the first and second parts, results show that at 750~850 oC, two kinds of ASC using ammonia as a fuel have almost the same cell performance as hydrogen-fueled SOFCs. This is because at 750 oC and above ammonia decomposes into H2 and N2, then following by H2 oxidation reaction to form H2O. Regardless of fuels (ammonia or hydrogen), the cell performance increases with increasing p and T. It is found that the ohmic polarization resistance is independent of p, but it decreases with increasing T. The total polarization resistances decrease with increasing T and p. The cell with different cathode material of LSC has higher electronic conductivity than LSCF, so it has better cell performance. The stability test of ASC is conducted at 750 oC under both 1 atm and 3 atm and at 0.8 V. After 90 minutes stability test, the cell of ASC fueled with ammonia has no degradation, even with a slight increase of power density (1-3%).
The third part shows that increasing the flow rate of ammonia cannot increase the cell performance when the temperature at 600 oC and below. Because increasing the flow rate can decrease the fuel residence time and the ammonia decomposition decreases with decreasing the residence time, resulting in the lower hydrogen concentration in the vicinity of anode. Thus the increase of flow rate can result in an increase of the total polarization resistances, since the product and nitrogen can increase the gas diffusion. The fourth part is to compare the pressurized effect of ASC which has different reactive area. From the EIS data, we find that the smaller reactive area of ASC is dominated by the gas diffusion having characteristic frequencies between 10~100Hz. For the larger reactive area of ASC, the dominated polarization is via gas conversion having characteristic frequencies less than 1 Hz. Such difference is that the larger reactive area of ASC can consume the fuel faster, resulting in less fuel and more product in the outlet gas which in turn increases the gas conversion resistance. The total polarization resistances decrease with increasing p for both small and large reactive area of ASCs, indicating that pressurization increases the cell performance. These results should be useful for the future development of ammonia SOFC power generation system. |
