操作參數、電解質及流道設計對直接甲醇燃料電池甲醇穿透 及性能之影響

Effects of operation parameters, electrolytes and flow fields on the DMFC crossover and performance

杜承鑫(Cheng-Hsin Tu)

指導教授 ： 蘇艾

元智大學/工程學院/機械工程學系/博士(2007年)

https://doi.org/10.6838/YZU.2007.00327

摘要

影響直接甲醇燃料電池性能之因素有許多，包含薄膜電極組的特性、甲醇穿透、甲醇濃度、電解質、觸媒、操作溫度、燃料種類及流率以及流道設計形式等。以機械工程的角度來看，可以研究的主題不外乎改變操作參數(溫度、流量、濃度、溼度等)、電池與流道設計。然而，本論文除了研究操作參數以及電池流道設計對性能效能之影響外，還深入自製薄膜電極組，改變電解質形式已研究不同電解質對性能及甲醇穿透之影響，更深一步進行不同流道之半電池模擬討論氣體濃度分布情形，與實驗結果相互印證。
根據研究成果，我們發現性能上升與操作溫度成正比但與膜材厚度成反比，儘管較薄的膜材會導致較多的甲醇穿透。然而，實驗也發現甲醇穿透的趨勢可以由開路電壓以及測量甲醇穿透電流來判斷。此外，由於直接甲醇燃料電池中陰陽極反應物與生成物之特性差異，我們更進一步的研究不同流道組合對其性能之影響。研究發現陰極流道設計對性能有較高的影響，故我們深入的討論陰極流道的效應，並藉由半電池模擬來驗證實驗之理論。研究中發現蛇形流道有較好的燃料分布特性然而柵狀流道則會有濃度貧瘠區產生。雖蛇行流道擁有較好之性能與穩定性，但若針對小型發電系統而論，其產生的高壓力差部分將會影響整體系統之發電效率。因此，針對各種流道進行壓力降測試，並考慮流道開放面積對於壓差以及性能之影響，結果發現使用棋盤流道有較小的能量損失且能提供適當的性能輸出。

關鍵字

直接甲醇燃料電池 ； 甲醇穿透 ； 濃度貧瘠

並列摘要

The performance of direct methanol fuel cell (DMFC) was affected by many factors; include membrane electrode assemblies, methanol crossover, concentrations, electrolytes, catalysts, temperatures, flow field design and so on. In this study, we do lots of investigations of the effects of operating parameters, electrolytes (Nafion 211, 112, 117, Nx-424), flow fields designs and combinations on DMFC performance and efficiency.
According to the results, we find the performance increase with the increasing temperature and decreasing membrane thickness no matter the thin membrane cause more methanol crossover. However, the tendency of methanol crossover can be determined by open circuit voltage and crossover current densities measured via electrochemical oxidation technique. In addition, the experiments with flow field designs and different stoichiometric factor were investigated to see the influences of the DMFC with the different combinations as a result of entirely different characteristic of reactants and products in anode and cathode of DMFCs. Among these, cathode flow field holds higher influence than that of anode. However, more detailed experiments needed to be done to find out the reasons. In this study, CFDRC half-cell models are adopted to simulate the flow phenomena within flow fields. We find that gas is well distributed within serpentine flow field while barren region are observed within parallel flow field. In the conclusion, balance the energy demand and the performance export of DMFCs system by using grid flow field design to supply oxygen to the cathode can be verified.

並列關鍵字

Direct Methanol Fuel Cell ； crossover ； barren region

參考文獻

[1] K. Kordesch, G. Simader, Fuel Cells and Their Applications, VCH, Weinheim, 1996

[3] J. Cruickshank, K. Scott, J. , 1998, Power Sources 70, pp 42.

[7] A. Eisenberg and H. L. Yeager, Perfluorinated Ionomer Membranes ACS Symposium Series 180, American Chemical Society, Washington, DC (1982).

[9] V. Tricoly, 1998, J. Electrochem. Soc., 145, pp 3798

[11] T. L. Yu, H. L. Lin, K. S. Shen, L. N. Huang, Y. C. Chang, G. B. Jung, and S. H. Chan, 2005, J. Power Sources, 150, pp 11.