微孔層結構對質子交換膜燃料電池 內之陰極氣體擴散層兩相流影響分析

Abstract

本研究分成兩個部分，第一個部分是設計一個孔隙度線性變化的氣體擴散層，利用兩相流的理論，對質子交換膜燃料電池的陰極氣體擴散層內，液態水飽和度以及氧氣濃度分析。研究中發現，依據兩相流理論，在觸媒層產生的液態水，會阻塞孔道，影響氧氣傳輸，利用此氣體擴散層，能夠增加排水性，增進電池的效率。而滲透率較小，以及接觸角增大，對氣體擴散層內的液態水以及氧氣傳輸，皆有幫助。而第二個部分則是在氣體擴散層接近觸媒層的那一側，加入一層薄的微孔層，因為在孔狀結構裡，液態水的傳輸主要是靠毛隙壓力，所以在氣體擴散層和微孔層的介面，我們可以從壓力連續的條件，來求得此介面的液態水飽和度，藉由此方式來探討當氣體擴散層和微孔層相互之間不同的性質時，對液態水飽和度，以及氧氣濃度的影響。

This study can be divided into two parts. The first part is that to design a gas diffusion layer with linear porosity. Analyzing liquid water saturation and oxygen concentration distribution in gas diffusion layer of cathode gas diffusion layer of PEM fuel cells by using two-phase flow model. We find liquid water due to chemical reactions reduces effective porosity of gas diffusion layer and hinders oxygen transport to reaction site. When the permeability decreases or the contact angle increases, the liquid water saturation and oxygen concentration distribution in gas diffusion layer would be better. The second part is to put a micro-porous layer on the catalyst side of gas diffusion layer. Liquid water transportation is governed by capillary action in pore structure, therefore , the gas and liquid pressure across the interface of these two layers are continuos. The effects of gas diffusion layer and micro-porous layer composed of two materials and characteristics are elucidated.