應用兩相流模式分析質子交換膜燃料電池陰極氣體擴散層參數影響

Abstract

本文推導出一個針對質子交換膜燃料電池的兩相流模式，模式中探討了質子交換膜燃料電池在不同的操作條件和設計參數下，物種在氣體渠道、氣體擴散層和觸媒層內部之傳輸行為，預測電流密度在觸媒層和質子交換膜的生成情形，以及比較其極化曲線和最大功率和設計參數間的關係。本文主要研究氣體擴散層中孔隙度和厚度的變化對於質子交換膜燃料電池性能的影響，除此之外，質子交換膜燃料電池操作溫度變化對入口條件的改變對於質子交換膜燃料電池性能的影響也一併探討。 藉由電化學反應產生之液態水，會佔據多孔性材質內部的孔隙體積，並造成氣體擴散層內部溢流的現象發生。本文的結果顯示，液態水佔據孔隙體積的影響並不顯著。從文中計算的結果中得到以下主要的結論: 1. 質子交換膜燃料電池性能會隨著孔隙度的增加、較薄的氣體擴散層厚和較低的操作溫度而上升；2. 最大功率密度和氣體擴散層孔隙度呈一指數型態的關係式；3. 最大功率密度和氣體擴散層厚度呈一線性型態的關係式。

A one-dimensional, steady-state, isothermal, two-phase flow model has been adopted to analyze the performance of a single proton exchange membrane fuel cell (PEMFC). The model describes the distributions of species at gas channel, gas diffuser layer (GDL), and catalyst layer and predicts the current density generated at catalyst layer and membrane of various operating conditions and design parameters. An investigation of the effect of change of porosity and thickness of GDL on the performance of a PEMFC is made at this study. Besides, the effect of change of operating cell temperature which affects the inlet conditions is also discussed. The liquid water, which produces by electrochemical reaction, occupies the volume of pores and results in the flooding of GDL. The results show that the influence of saturation level (the volumetric fraction of the void space occupied by the liquid water) is not significant. It is found that the performance enhances with higher porosity, thinner diffuser layer and lower operating temperature. The relation between maximum power density and porosity seems to be a convex exponential function. The relation between maximum power density and gas diffuser thickness is a linear function.