質子交換膜燃料電池內水傳輸之暫態分析

Abstract

本文使用數值模擬來探討質子交換膜內水傳輸的現象，研究著重在氣體擴散層、觸媒層及質子交換膜內水濃度分佈的暫態行為。在質子交換膜內主要考慮擴散效應與電滲透效應對液態水傳輸所造成的影響；而在氣體擴散層與觸媒層內的氣態水傳輸，則僅考慮擴散作用的影響。而在質子交換膜與觸媒層的介面處，則以質子交換膜的吸水(water uptake)特性來處理。利用多個不同的操作條件設定，來探討不同操作條件對電池內水傳輸現象的影響。 研究結果顯示速率常數的大小對質子交換膜內水含量分佈的影響很大，較大的速率常數會使得薄膜內水含量較高，且到達大致平衡所需的時間也較短。在加濕量不足的情況下，質子交換膜內的水含量不但明顯偏低，連達到平衡所需的時間也大為增長。另外，不同的質子交換膜厚度，也會對薄膜內的水含量分佈有很大的影響，在質子交換膜厚度較薄的情形下，薄膜內的水含量分佈較平均也較高，而達到平衡所需的時間明顯較短。

A one-dimensional, isothermal, transient mathematical model is adopted to investigate the transient water transport behavior in membrane of the proton exchange membrane fuel cell (PEMFC). The water transport in the membrane is affected by diffusion of water and the electro-osmotic drag. The water concentration distribution in catalyst layer and gas diffusion layer concerns only the diffusion of water. The investigation of water transport transient behavior affected by different operating conditions is made at this study. The results show that the influence of different operating conditions on water transport behavior is significant. With higher humidification rate constant, k, the magnitude of membrane water content is higher and the time needed to achieve the water content balance is less. The water content of membrane reduces and time needed to reach stable is longer when the humidification is not sufficient. When the thickness of membrane is thinner, the water content of membrane is more uniform and higher, and the time for the water content become stable is shorter.