A Quasi-Two Dimensional Analytic Solution for the Cathode Side Half-Cell Model of Proton Exchange Membrane Fuel Cell

本論文針對質子交換膜燃料電池陰極側的內部傳輸現象進行分析與研究。論文中假設操作條件為等溫、穩態，燃料的變化情形在流道部分僅隨沿著流道方向做改變，當進入氣體擴散層後的傳輸則僅考慮擴散效應所以分布只隨穿越薄膜方向而改變。最後解出一套可描述電池內部傳輸現象的解析解以供討論。而本文更利用此解析解，進而改變不同的操作條件參數來探討其對電池性能的影響性。 在本文中得知，氣體擴散層的孔隙度分布愈大，則可以傳輸至觸媒層的燃料增加，所以可提升電池性能。而氣體擴散層的厚度上則是愈薄愈好，因為過厚的電極裝置對使得燃料傳輸路徑變長，因而減少了可供觸媒層反應的燃料量，因此電池性能會降低。對於觸媒層的考慮上，太厚或太薄的觸媒含量對於電池性能都不好，因為厚度過厚會造成較大的歐姆阻抗產生，而太薄時又會使得反應速率變慢，無法有效提升性能，所以對於燃料電池中觸媒層的含量問題，應該經由嚴謹的討論設計，以便找出最佳化範圍可供相關人員參考。而質子交換膜應該盡量設計的愈薄愈好，因為其厚度增加，電池也會因為歐姆阻抗的增加造成性能下降的情形。最後由局部位置分析傳輸現象得知，氣體流道的設計往往也會影響到電池性能的好壞，例如在流道長度的最佳化設計上、流道類型的使用、或是檔板的應用情形等，都有待相關單位進一步的探討。由於本文中並不考慮水的效應對於電池的影響，所以所提供的結果僅在排除水的情形下才適用。The principle concern of this study is about the oxygen transport situation in the cathode side of PEM fuel cells. A steady state and isothermal half-cell model is considered in the present study. It is assume that the oxygen concentration in the gas channel changes in the channel direction. While in the gas diffuser layer, the oxygen concentration varies across the membrane in the membrane direction. We successfully obtain an analytical solution that describe the phenomenon relate to oxygen transport and membrane phase potential. This solution can be used to analyze fuel cell performance with variable operating parameter. It shows that increasing the porosity of gas diffuser layer allows more oxygen to diffuse across the catalyst layer and improves the cell performance. A thin gas diffuser layer thickness is better than a thick one, because too thick gas diffuser layer makes the transport route longer and resulting in less oxygen could participate in the catalyst and then reduce the cell performance. Considering catalyst layer thickness, catalyst layers that are either too thin or too thick do not give satisfactory results, because a thin layer would lead to lower reaction rate, while a thick layer would form higher Ohm resistance. Therefore, there exists an optimum thickness of catalyst layer. Considering the membrane thickness, it is found that a thick layer would increase cell resistance and eventually reduce the cell performance. Finally, base on the results at different locations it is discovered that oxygen distribution in the gas channel always influences the cell performance. Hence, the discussions and analysis of gas channel design for fuel cells are necessary. Since the cell present study does not consider water effect, all result presented in this work were based on the situation without water.目錄 中文摘要…………………………………………………………………I 英文摘要………………………………………………………………..III 表目錄…………………………………………………………………...V 圖目錄…………………………………………………………………...V 符號說明……………………………………………………………...VIII 第一章 序論……………………………………………………………..1 1.1 燃料電池的發展………………………………………………….1 1.2 燃料電池的本原理……………………………………………….2 1.3 燃料電池種類…………………………………………………….3 1.4 文獻回顧………………………………………………………….5 1.5 研究主題…...……………………………………………………10 第二章 理論分析………………………...…………………………….12 2.1 基本假設………………………………………………………...12 2.2 統御方程式……………………………………………………...13 2.2.1 氧氣傳輸現象…………………………………….………...13 2.2.2 薄膜相電位....…………………………………….………...15 2.2.3 電流密度………………………………………….………...17 2.2.4 電池電壓………………………………………….………...18 第三章 結果與討論……………………………………………………20 3.1 基本操作條件(base case)下之結果分析…………...………...20 3.1.1 濃度分布之結果….………………………………………...20 3.1.2 薄膜相電位分布之結果….………………………………...21 3.1.3 電流密度分布之結果….…………………………………...22 3.1.4 I-V、I-P性能曲線之分布…………………………………...23 3.2 氣體擴散層之分析……………………………………………...23 3.2.1氣體擴散層孔隙度對濃度影響之分析……………………..23 3.2.2氣體擴散層孔隙度對薄膜相電位影響之分析...…………...24 3.2.3氣體擴散層孔隙度對電池性能影響之分析……………......25 3.2.4氣體擴散層厚度對濃度影響之分析………………………..26 3.2.5氣體擴散層厚度對薄膜相電位影響之分析………………..26 3.2.6氣體擴散層厚度對電池性能影響之分析…………………..27 3.3陰極觸媒層之分析………………………………..……………...27 3.3.1陰極觸媒層厚度對濃度影響之分析………………………..27 3.3.2陰極觸媒層厚度對電池性能影響之分析…………………..28 3.4質子交換膜之分析……………………………..………………...29 3.5水平x方向之局部特性分析……………………………………..29 3.5.1不同x位置下的濃度分析………………….………………..29 3.5.2在x=0時的特性分析…………….……………………………..30 第四章 結論與建議……………………………………………………56 4.1 總結……………………………………………………………...56 4.2未來研究方向與建議……………….…………………………...57 參考文獻………………………………………………………………..58 Appendix....…………………………………………………………….6