合成氣固態氧化物燃料電池性能與穩定性量測;Measurements of cell performance and stability for syngas solid oxide fuel cells

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Title:	合成氣固態氧化物燃料電池性能與穩定性量測;Measurements of cell performance and stability for syngas solid oxide fuel cells
Authors:	張華屹;Chang, Hua-Yi
Contributors:	機械工程學系
Keywords:	加壓型固態氧化物燃料電池;合成氣;電池性能;電化學阻抗頻譜;Pressurized SOFC;Syngas;Cell Performance;Electrochemistry Impedance Spectroscopy
Date:	2018-01-29
Issue Date:	2018-04-13 11:30:05 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究使用陽極支撐鈕扣型全電池於已建立之加壓型固態氧化物燃料電池(SOFC)實驗平台，量測合成氣(35% H2 / 65% CO)燃料，在不同操作環境下，其電池性能以及電化學阻抗頻譜之變化。當操作溫度從750°C提升到850°C，合成氣操作在0.8 V下之電池性能，可從947 mWcm-2增加到1146 mWcm-2，提升了21%。這是因為溫度上升可以提升電解質的離子傳導性，進而降低電池歐姆阻抗，同時也可減小活化極化。使用合成氣在750°C從1大氣壓加壓至3大氣壓，電池開路電壓(open circuit voltage, OCV)和最大功率密度均有明顯的提升，這是因為加壓可以增加反應氣體的體積莫耳濃度也可以增加電極表面的氣體覆蓋率，進而減少濃度極化和活化極化，但歐姆阻抗則不受操作壓力的影響而維持定值。在合成氣燃料加入3% H2O操作於700°C時，會因為水分子堵塞氣體擴散之孔洞，進而並降低反應速率，造成電池性能和OCV降低。使用合成氣在一大氣壓分別於700°C和750°C下進行電池穩定性測試，發現操作在750°C時，電池可以穩定操作25小時幾乎沒有性能衰退。但在700°C時，碳沉積明顯出現，甚至會造成陽極氣體管路的堵塞。所以，使用合成氣為燃料時，於常壓下溫度應高於700°C，以避免嚴重之碳沉積問題。同樣地，使用合成氣於750°C和3大氣壓條件下，進行電池性能穩定性測試，電池性能可維持穩定一段時間，10小時之後，碳沉積會越來越嚴重，逐漸影響電池性能，造成電池性能衰退。所以，在加壓條件下，需要更高的操作溫度來克服碳沉積的問題。在700°C條件下，進行乾和加濕(3% H2O)的合成氣穩定性實驗的比較，發現加濕之後可使電池維持穩定操作37小時，這是因為水可以和碳發生反應，降低碳沉積的影響。以上之實驗結果，有助於了解合成氣於SOFC在不同操作環境之碳沉積現象和電池性能變化，這對未來 SOFC 欲使用合成氣為燃料進行發電，在基礎知識上，有所助益。;This thesis applies the anode-supported cell to test the cell performance and electrochemical impedance spectroscopy at different operating conditions using syngas (35% H2 / 65% CO) as a fuel in a pressurized solid oxide fuel cell testing platform. When the operating temperature increases from 750°C to 850°C, the cell performance at 0.8 V increases from 947 mWcm-2 to 1146mWcm-2. Because the increase of the operating temperature can enhance the ionic conductivity of the electrolyte which can reduce the ohmic impedance and also it can reduce the activation polarization. The usage of syngas at elevated pressure from 1 atm to 3 atm at 750°C can significantly increase the open circuit voltage (OCV) and the power density. This is because pressurization can increase the molar concentration of the reaction gas and the gas coverage on the electrode surface, thereby reducing concentration and activation polarizations. However, the ohmic resistance remains the same independent of pressure. The addition of 3% H2O to syngas fuel at 700°C results in the reduction of cell performance and OCV. This is because the water molecules can block the pores of gas diffusion and reduce the reaction rate. The stability tests of syngas SOFC under atmospheric pressure at two different temperatures: 700°C and 750°C show that at 750°C the cell can be stably operated for 25 hours without any decay of cell power density. But the carbon deposition appears at 700°C getting worse with time and eventually blocking the anode gas pipeline. Thus, when using syngas as a fuel at 1 atm, the cell operating temperature should be higher than 700°C to avoid serious carbon deposition problem. Similarly, we conduct the cell stability test at 750°C and at 3 atm. Results show that the cell performance can remain stable for a period of time up to 10 hours. After 10 hours, the carbon deposition starts to appear and the cell performance is gradually decaying. Hence, at elevated pressure, the higher operating temperature above 750°C is needed to overcome the carbon deposition problem. Moreover, at 700°C, we compare the stability tests of both dry and humidified (3% H2O) syngas SOFCs. Results show that the humidification can extend the cell longevity. This is because water can react with carbon resulting in a decrease of carbon deposition. Finally, these results help our understanding of syngas SOFCs operated at different conditions and their associated carbon deposition phenomena, which should be useful for future power generation.
Appears in Collections:	[Graduate Institute of Mechanical Engineering] Electronic Thesis & Dissertation

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