質子交換膜型燃料電池膜電極組內觸媒分布形式對性能之研究分析

Abstract

本論文主要研究方向為質子交換膜燃料電池的心臟--薄膜電極組，薄膜電極組佔整顆電池成本約80%，因此若能減低薄膜電極組的製造成本，無疑能減少燃料電池整體的花費。 本文中採用傳統疏水性方法製造觸媒電極，並以中科院所製之MEA效能作為比較。MEA之組成如三明治般，由氣體擴散層，觸媒層，高分子電解質膜，氣體擴散背層等結構結合而成，每一層結構之含量差異或不同類型都會對性能造成影響。 石墨雙極板的鏤空流道處主要是氣體反應區，肋條則為電子傳送區域，若加大流道-肋條比，則可使反應氣體增加，但卻減少電子傳輸路徑。本實驗主要將電極製作方法分成流道區和肋條區，採取不同分佈方式塗佈觸媒，或是在不同區域製作氣體擴散層等方法，研究不同類型的MEA對性能有無影響。 實驗得知，氣體會通過觸媒層進行反應，當觸媒大部分分佈於流道區時，在低電流密度，氣體會滲入被遮蔽的肋條底下，但肋條底下觸媒存在少，因此對性能無助益。而當電流密度提昇時，氣體消耗速率加快，會有較少的氣體滲入肋條端，此時加重流道處的觸媒量，可以提升性能。若增加肋條端氣體擴散層的厚度，可增進質傳效果，因為在傳輸方向增加了氣體的輸送路徑，使傳輸限制降低，氣體可以充分進行反應，使性能也相對的提升。 本文對於MEA的製作方法不同於以往，可看出某些方法對於MEA性能有所改善，若能將這些製程制式化，甚或減少材料用量，則可對於燃料電池成本降低有所助益。

This paper focuses on the heart of PEMFC (Proton Exchange Membrane Fuel Cell)—Membrane Electrode Assembly. The MEA accounts for about 80% of whole cell cost. If we can lower the manufacturing costs of the MEA, then we can reduce the whole cost of fuel cell. In the paper, we adopt the traditional hydrophobic method to make the catalyst electrode, and compare the efficiency with the MEA made by Chung-Shan Institute of Science and Technology. The structure of MEA is like sandwich, made up by gas diffusion layer, catalyst layer, polymer electrolyte membrane, and backing layer. The different composition of each layer would lead to the different performance. The hollow channel part of the graphite bipolar plate is mainly the gas reacting area, and the rib part conveys the electron. If we strengthen the ratio of flow and rib, we can make reacting gas increase. However, this action would reduce the electron transmission routes. This experiment divides the manufacture method of the electrode into two parts- flow area and rib area, also take different ways to coat catalyst layer or make the gas diffusion layer on the different areas, etc. Through this experiment, this paper aims at investigating whether the different kinds of MEA will have a influence on performance of MEA. From the experiment, we can learn that, when the catalyst is mostly distributed on flow channel, the gas would react thought the layer, and at low current density, the gas would permeate into the part covered by the rib. However, there is a bit of catalyst under ribs, so it’s not helpful to the performance. And at high current density, the gas consuming rate increase, and less gas would permeate into the rib part.At this time, if we raise the catalyst amount of flow part, then we can improve the performance. If we increase the thickness of gas diffusion layer under rib area, we can promote the mass transmission, because the gas would fully react after we increase the gas transport route of transmission direction to reduce transmit limiting.In comparison, the performance would improvement. The manufacture practiced in this paper is different from what has been done in the past. We can find that some methods would improve the MEA performance. If we can make the procedure more general, or reduce material consumption, then can reduce the fuel cell cost helpfully.