| 摘要: | 本論文使用已建立之高壓測試平台，搭配鈕扣型實驗載具，針對加壓型SOFC陽極支撐全電池(Ni-YSZ/YSZ/LSC)，量測其使用甲烷燃氣所產生之碳沉積效應，以及相關之性能曲線(I-V curve)與電化學阻抗頻譜(Electrochemical Impedance Spectra, EIS)。實驗條件為固定氣體流率(陽極50 sccm CH4+150 sccm N2和陰極200 sccm Air)，並控制電池負載(0.9和0.8V)、系統操作壓力(p = 1和3atm)和系統溫度(T = 750和800oC)。結果顯示，壓力和溫度增加皆會使電池性能有效提升，兩者皆可使總極化阻抗減小，但歐姆阻抗則與加壓效應無關，其僅會隨溫度增加而下降。
為詳細探討電池負載、加壓和溫度效應對於碳沉積之影響，我們進一步作性能穩定性測試。結果顯示，當電池在較高的負載下，可有效抑制碳沉積的產生，例如:在溫度800oC與壓力1 atm下時，0.8V可穩定操作達120分鐘，0.9V則會隨時間持續衰退無法穩定。加壓和升溫理論上會加快碳沉積形成之速率，但因電池性能會同時受加壓和升溫影響而提升，故提高了水與二氧化碳的濃度，它們可增加除碳作用。整體電池性能是否可達到穩定，必須取決於壓力、溫度和電池負載間的交互影響。最後，使用氫氣移除碳沉積，證實碳沉積可被氫氣移除，但移除後電池性能較移除前低。這可能是因為碳沉積已些微破壞電池微結構，造成無法完全回復原電池性能。本研究結果，應有助於了解加壓型SOFC使用甲烷燃氣所形成之碳沉積現象，值得一提的事，本研究為國際上首度利用實驗，來進行壓力效應對碳沉積之研究，這對未來開發加壓型SOFC與微氣渦輪機複合式發電系統應有所助益。
;This study applies an established high-pressure SOFC testing platform together with a button cell experimental setup, so that the impact of carbon deposition on the cell performance, electrochemical impedance spectroscopy (EIS), and stability tests of an anode-supported button full cell can be analyzed when using methane as a fuel. Fixed flow rates are used for all experiments (CH4 + N2: 50 +150 = 200 sccm in anode and air: 200 sccm in cathode) at two different cell loads (0.9V, 0.8V), temperatures (750, 800oC) and pressures (1, 3atm). Results show that cell power densities increase with increasing p and T. It found that the ohmic polarization resistance is independent of p, but it decreases with increasing T. The total polarizaiton resistances decrease with increasing T and p.
To investigate effects of operational parameters i.e. cell loading, temperature, and pressure on carbon deposition, we further conduct the stability test of the cell performance. Results suggest that increasing the cell loading can inhibit effectively carbon deposition. For example, when T = 800oC and p = 1 atm, the cell performance is stable at 0.8V for at least 120 minutes but degradation of performance is found at 0.9V. Though increasing T and p can promote methane cracking rate, cell performance can be also enhanced simultaneously resulting in higher concentrations of H2O and CO2 that remove carbon effectively. Therefore, the stability of cell performance depends on interactions of cell loading, temperature, and pressure. After the stability test of cell performance, we apply hydrogen for the reduction of carbon deposition. The result shows that carbon can be removed by using hydrogen but the original performance can not be fully recovered. The present study should be useful for understanding the carbon deposition phenomenon when using methane as the anode fuel. Generally, the power density increases due to pressurization. However, the effect of pressure must be combined with loading and temperature effects to determine whether cell performance can be stable. To the best knowledge of the authors, it is worth of noting that the aforesaid pressurization effect on carbon deposition is the first available experimental investigation in literatures, which should be useful in the development of pressurized SOFC integrating with micro gas turbines for hybrid power generation systems. |
