摘要 本論文旨在研究質子交換膜燃料電池(proton exchange membrane fuel cell，PEMFC)之雙極板的替代性材料，採用具有彈性的熱塑性聚 胺酯 (Thermoplastic Polyurethane，TPU)，欲藉由高分子材料本身的 彈性，增加雙極板於燃料電池組裝上的氣密性，取代氣密墊圈的使 用，且降低材料與製造的成本。 研究中使用不同的導電填充物與比例，以熱壓成型的方式製備高 分子複合材料，由實驗結果可以發現，導電填充物對材料的機械性質 可提升強度硬度與吸震的效果，由熱傳導係數的量測，可得知導電填 充物對材料熱性質的影響，再從自行架構的電阻率量測系統以定電流 輸出量測，可得知試片在固定夾持力下的體電阻值，使用掃瞄式電子 顯微鏡觀測試片中導電性材料的分布情況，最後藉由田口式實驗計劃 法，找出最佳化的導電填充物添加比例與混練參數，並製備出高分子 複合材料燃料電池雙極板。 最佳化的導電填充物添加比例為碳纖維添加30wt%與XC-72 碳 黑添加30wt%。為模擬燃料電池的操作溫度，因此藉由溫升電阻率量 測系統，探討溫度上升時對電阻率的影響。最佳添加比例的複合材料 試片具有正溫度係數效應，由室溫30°C 升溫至90°C時電阻率由0.396Ω-cm 上升至0.424Ω-cm。 本研究最後使用高分子複合材料雙極板進行燃料電池性能測 試，在實驗中分別對組裝鎖緊扭矩、電池溫度與增濕溫度之不同參數 下進行研究。燃料電池組裝時，雙極板與膜電極之間不使用氣密墊 圈，當組裝鎖緊扭矩達3N-m 時，即可達到氣密的效果；而鎖緊扭矩 為3.5N-m 時，可降低接觸阻抗獲得較佳的電池性能；在未加濕的條 件下改變電池操作溫度進行性能測試，結果發現高分子複合材料雙極 板受正溫度係數效應影響，電池操作溫度在50°C 時電池性能最佳； 固定入口氣體溫度，改變加濕溫度進行測試，當加濕溫度為80°C 時， 可獲得較佳的電池操作性能。測試結果發現較佳的電池性能，在定電 壓0.6V 放電下，電流密度可達650mA/cm2 以上。 Abstract The purpose of this study is to investigate the effects of various carbon materials on the mechanical, thermal and electrical properties of polymer composites. These composites materials are potential replacements for graphite bipolar plates currently used in proton exchange membrane fuel cells (PEMFC). Polymer composites are fabricated by the hot press method using different mixing ratios of conductive fillers and TPU. In this work, acetylene black (AB), carbon black (XC-72), carbon fiber, and graphite are used as the conductive fillers. The results show that as the content of the conductive fillers increases, the mechanical strength, the hardness, and the vibration-absorption ability of the composite increase. The thermal conductivity also increases. The electrical resistance decreases as the filling ratio of the conductive fillers is increased. Of the four fillers, carbon fibers and XC-72 carbon black samples have the lowest resistance. The Taguchi method is used to study the optimal content of the conductive fillers and process parameters. The best mixing speed and time are found to be 50rpm and 4 minutes, respectively. The optimal filling content is 30wt% of carbon fiber plus 30wt% of XC-72. This best sample shows a slightly positive temperature coefficient of the resistance. It increases from 0.396Ω-cm at 30 °C to 0.424Ω-cm at 90 °C . Finally serpentine flow channel bipolar plates are fabricated using the optimal design and are assembled with a Gore MEA to a single cell PEMFC. NO gaskets are used between the MEA and the bipolar plate. Gas tight is achieved with a torque of 3N-m. For cell temperature of 50°C and humidification temperature of 80°C , the current density reaches 650 mA/cm2 at voltage 0.6 V.
