氣體擴散層的壓縮不均勻效應對質子交換膜燃料電池之性能影響

The compressed non-uniformity effect of gas diffusion layer on PEM fuel cell performance

紀丕鴻(Pei-Hung Chi)

指導教授 ： 詹世弘

元智大學/工程學院/機械工程學系/博士(2007年)

https://doi.org/10.6838/YZU.2007.00270

摘要

質子交換膜燃料電池(Proton Exchange Membrane Fuel cell‚PEMFC)的組裝過程中，必需陰陽極兩端的端板(或壓板)加壓鉗住燃料電池，其目的不外乎防止漏氣及減少接觸阻抗。但是加壓的結果在流場板的肋條部分會對氣體擴散層(Gas Diffusion Layer, GDL)產生擠壓效應，而流道部分則不受擠壓，使氣體擴散層(GDL)以受壓與否而產生不均勻週期性方波型的孔隙度(porosity)及滲透性(permeability)分佈。氣體擴散層(GDL)是質子交換膜燃料電池的主要元件之一，其目的包括(1)固接觸媒層，(2)傳遞反應物(燃料或氧化物)至觸媒層，(3)排除生成水，(4)散熱及(5)傳導電子等功能。所以不均勻的孔隙度及滲透性分佈，將嚴重的影響氣體擴散層的效能。
本研究的目的以實驗和數值，分析氣體擴散層因鉗緊固裝力量的作用造成不均勻孔隙度及滲透性分佈，對燃料電池性能影響。在實驗中以各種不同厚度的墊圈控制氣體擴散層的壓縮比，測試燃料電池性能。相對應壓縮比的數值模擬，是以有限容積法的計算流體力學求解。建立三維質子交換膜燃料電池物理模型，以商用計算流體力學CFD-ACE+ 2003軟體，同時模擬電化學動力、電流分布、流體動力及多成分傳輸現象。數值模擬的結果與實驗比較，整體燃料電池性能上，獲得良好的一致性。因為以往的數值研究都假設為均勻壓縮氣體擴散層模式，本文進一步詳細的研究針對比較不均勻壓縮模式和相對等效均勻壓縮模式的作用，同時考量滲透性(permeability)亦隨孔隙度而改變。結果顯示不均勻的壓縮性導致高電流區域明顯的濃度極化。此外，不均勻壓縮會造成在肋條下方被壓縮的氣體擴散層有更高的電傳導性，更多生成水被保留在肋條下方的膜，導致上游膜的導電性增加，但是到了下游則應液態水會過多，而形成水氾濫。最後，探討不同壓縮效應對水和熱管理及電流密度、溫度，和成分的分佈情形，以作為未來最佳化設計PEM燃料電池的參考。

關鍵字

氣體擴散層 ； 非均勻氣體擴散層結構 ； 壓縮氣體擴散層 ； 數值模式 ； 燃料電池

並列摘要

The present study investigates both experimentally and theoretically the effects on fuel cell performance of non-uniform porosity and permeability in the gas diffusion layer (GDL) due to clamping force. In the experimental study, various kinds of gaskets are used to simulate various compression ratios of the GDL. In the theoretical simulations, a relevant GDL compressed model and a three-dimensional proton exchange membrane (PEM) fuel cell model are developed to simulate multi-physic transport based on code from the Computational Fluid Dynamics Research Corporation (CFDRC). The results of the numerical simulation are compared and showed in good agreement with that of experiments in overall fuel cell performances.
Further detailed investigations are made in comparing the present non-uniformly compressed model with its commonly assumed uniformly compressed model. It is shown that, although both models yield almost the same total performance at working voltage range, their local distribution characteristics are far different such that the uniform compressed model can not predict well the local phenomena. Also, the distributions of temperature, heat flux, species concentration, current density and saturation are found to be highly oscillating in nature between the local rib and channel locations. Furthermore, the higher the compression ratio, the better is the cell performance and the larger is the fluctuation amplitude. Finally, the higher the compression ratio, the more are the saturation, water flooding and hydrogen deficiency downstream. More detail compression effects on membrane conductivity, etc, are also presented.

並列關鍵字

Gas diffusion layer ； Non-uniform GDL structure ； compressed GDL ； numerical modelling ； fuel cell

參考文獻

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