水、熱管理在燃料電池中為一相當重要之因素，在本篇論文之研究中，將會探討氣體擴散層(GDL)、微孔層(MPL)與流道特徵參數對於燃料電池之放電性能影響。內容分為實驗與理論兩部分，分別為以實驗設備進行不同氣體擴散層與微孔層的氣體滲透率、孔隙率、孔隙大小與表面結構的測量，並結合碎形理論以分析其物理特性對於氣體滲透率與熱傳導係數的影響。 實驗係對MPL的有無、厚度、PTFE含載量、製程時間等因素對GDL特性之影響進行研究，其結果顯示，在燃料電池中使用MPL可有效的增加排水的能力，並可提升電池性能。並發現MPL之燉燒製程時間可增加氣體滲透率與孔洞大小，造成電池性能提升。 理論分析中也藉由碎形理論分析氣體滲透率與氣體擴散層的熱導率。在氣體滲透率中，使用碎形串聯模型來推算其GDL與MPL的氣體滲透率。模型中，主要考慮孔洞尺寸，孔隙率，碎形尺寸等等參數進行分析。此外，模型中同時考慮微小氣體分子流動對滲透率的影響。在GDL的熱傳導率上，同樣也藉由碎形理論分析其熱傳導現象，研究結果顯示，其熱傳率主要取決於樣品的孔隙率，並且使用不同含量的黏著劑對於熱傳率的影響不大。 Water and thermal management is an important issue in proton exchange membrane (PEM) fuel cell design and operation. The purpose of this work is to investigate the effects of the microstructure characteristics of the gas diffusion layer (GDL) and microporous layer (MPL) on the water management and performance of a PEM fuel cell. The microstructure characteristics studied include pore size, pore size distribution, pore shape, and hydrophobic treatment. In the experiments, the effects of the MPL, the thickness of the MPL, the PTFE loading of carbon paper and MPL, and the baking time of the MPL have been investigated. Results show that the addition of MPL increases cell performance in the high current density region due to the elimination of mass transfer limitation. There exists an optimum thickness of MPL. Furthermore, increasing the MPL baking time enhances cell performance due to enlarged pore size and permeability. In the theory, a series fractal permeability model is developed to predict the gas permeability for the MPL and GDL in PEM fuel cells. The model is based on the maximum pore size, porosity, fractal areal dimension and fractal tortuosity dimension. The thicknesses of MPL and GDL are used in this model. In addition, the gas molecule effect is considered by using the Adzumi equation. According to the SEM images, two fractal dimensions are determined by the box-counting method. Moreover we also study the thermal conductivity by fractal theory, and we find that the porosity of GDL has strong effect on the thermal conduction.
