| 摘要: | 本研究針對鈕扣型(NiO-YSZ/YSZ/GDC-LSC)固態氧化物燃料電池(Solid Oxide Fuel Cell, SOFC)，以氨氣為主要燃料，分別對其進行加濕、加氫、改變溫度與陰極流率條件之實驗，藉此研究使用氨氣於不同條件下的電池性能。其中又以加濕氨氣的研究為主要重點，這是為了模擬垃圾掩埋場所產生之氨氮廢水成分，因此本實驗測試加濕氨氣適合在什麼環境下運作可以取得比較好的電池性能，以及探討氨氮廢水是否需要脫水才適合於SOFC使用。本研究使用實驗室已建立之雙腔體高溫高壓爐為主要測試平台，在不同的條件下進行測試。陽極燃料設計了七種不同H2/NH3/H2O/N2之體積濃度比例:(1) H2/N2 (120/80 sccm); (2) H2/H2O/N2 (120/20/60 sccm); (3) NH3/N2 (80/40 sccm); (4) NH3/H2O/N2 (80/20/20 sccm); (5) H2/NH3/N2 (30/60/50 sccm); (6) H2/NH3/H2O/N2 (30/60/20/30 sccm); (7) H2/NH3/H2O/N2 (30/60/40/10 sccm)。而陰極則是固定使用空氣，並以200、400、600、800、1000 sccm等五種不同的空氣體積流率來進行實驗。實驗結果顯示，氨氣與氫氣在添加水氣後性能都會下降，這可能跟陽極燃料體積流率和其反應面積比例有關，此比例越大代表會有剩餘的陽極燃料無法被陽極觸媒反應，而加濕時H2O在高溫的時候會在陽極鎳觸媒上裂解成氫氧根離子，進而佔據三相邊界之反應區域，造成性能下降。另外，本實驗針對氫毒化與H2O之交互影響進行實驗，將相同體積濃度之氫氣、氨氣以三種不同體積濕度(0%, 10%, 20%)進行電池性能與電化學阻抗頻譜量測。結果顯示：在700oC時加濕10%與20%之加氫氨氣的總阻抗都小於未加濕之加氫氨氣，推測是氫毒化被H2O產生之氫氧根部分消除，使得極化阻抗電池可以下降。最後，我們量測陰極流率效應，發現增加陰極流率會造成性能下降，其中歐姆阻抗上升，而極化阻抗下降，但總阻抗是增加的。原因可能是氧離子在三相邊界層過多，進而造成燃料匱乏所致；當陰極流率過高時，會有少部分氧離子到陽極與鎳觸媒結合成氧化鎳增加歐姆阻抗。另一種可能是陰極流率過大，造成電池表面溫度下降使歐姆阻抗上升。再者，H2O可能占據部分鎳觸媒，會進一步使電池性能下降。本研究針對加濕氨氣進行測試研究，其結果對於日後使用垃圾掩埋場所產生之氨氮廢水於SOFC發電應有所幫助。;This thesis investigates experimentally the cell performance of an ammonia button-type solid oxide fuel cell (SOFC) with the consideration of H2 and H2O in anode ammonia fuel at different operating temperatures and cathode air flow rates. We use the highly humidified ammonia gases to simulate the compositions of the ammoniacal nitrogen wastewater from the landfill. Thus, this study tests several different experimental conditions to find out a better cell performance of humidified ammonia-SOFCs and investigates whether the ammoniacal nitrogen wastewater needs to be dehumidified for the usage in SOFC. The experiments are conducted in an already established high temperature, high pressure double-chamber facility. The present anode fuels are designed with seven different H2/NH3/H2O/N2 volume ratios: (1) H2/N2 (120/80 sccm); (2) H2/H2O/N2 (120/20/60 sccm); (3) NH3/N2 (80/40 sccm); (4) NH3/H2O/N2 (80/20/20 sccm); (5) H2/NH3/N2 (30/60/50 sccm); (6) H2/NH3/H2O/N2 (30/60/20/30 sccm); (7) H2/NH3/H2O/N2 (30/60/40/10 sccm). In the cathode, we use air at five different flow rates, i.e. 200, 400, 600, 800, 1000 sccm. Results show that both hydrogen and ammonia cell performances decrease when doping with H2O. This may be attributed to the ratio of the anode flow rate and the effective area of anode surface, as hydroxyl radicals produced by H2O at high temperature can occupy the anode catalysts and suppress the electrochemical reactions of hydrogen and ammonia. This thesis also explores the possible relation between hydrogen poisoning and H2O addition in anode. By using the electrochemical impedance spectra (EIS), we obtain that when T = 700oC, the cases of (6) and (7) with the humidity of 10% and 20% have smaller total resistances as compared with the case of (5) with 0% humidity. It is thought that hydrogen poisoning can be eliminated partially by hydroxyl radicals. At last, we test the effect of cathode flow rate on the cell performance. The result surprises us that when we raise the cathode flow rate, the cell performance decreases. This situation may be caused by the “fuel starvation” in the anode; if sufficient oxygen ions come to the three-phase boundary on the anode side. Another possible reason may be cause by the excess cathode flow rate, it reduces the cell temperature and increases the ohmic resistance. It becomes more severe when doping H2O because hydroxyl radicals can occupy the anode catalyst nickel. Finally, these results may be of help for the possible usage of the ammoniacal nitrogen wastewater produced from the landfill in ammonia SOFC. |
