質子交換膜燃料電池電流密度分佈與水分佈之暫態分析研究

Transient Analysis of Current Density and Water Distribution on PEM Fuel Cell

辛銘仁(Ming-Jen Hsin)

指導教授 ： 郭景宗

國立臺灣大學/工學院/機械工程學研究所/碩士(2004年)

https://doi.org/10.6342/NTU.2004.10013

摘要

要得到好的操作性能，適當的水管理對質子交換膜燃料電池來說是不可或缺的。含水量不足將降低膜的傳導性，並造成高內電阻，而過多的水將導致電極的淹水，使反應面積減小。然而，水管理的困難在於不容易直接地觀察。
本實驗展示一個新的方法，利用透明流道板與分割電流收集板來量測區域電流密度與水分佈情形。每個分割電流收集板與鄰近區塊絕緣，並各別與分流器相接，以電流多通傳輸法來量測電流密度分佈；此外，利用數位相機擷取陰陽/極流道內液態水形成的影像，來解釋流道內不同區域淹水的反應機制，以暫態分析的角度，探討不同流道形式與操作條件對電池局部區域的影響。
實驗結果顯示，陰極端水分佈主要是從流道尾端往入口端擴散，而乾燥的情形則是從入口端往出口擴散；液態水凝結會從小水滴轉變成膨脹型水滴，進而造成流道的阻塞。流道入口區域，水分子主要藉電子拖曳力來傳輸，流道下游區域，水分子逆擴散的現象旺盛，使整體電流分佈形成出口與入口較高，中間區域較平均。進氣流量大會造成入口乾燥，性能下降，但流道內液態水較容易排除；流量小使入口處較濕潤，但流道內的液態積水嚴重。進氣溫度愈高入口處愈乾燥，並容易造成電池內部的液態水凝結。此外，多流道出口積水容易發生回流現象，使正常的反應區域縮小導致性能衰退；當大量積水排出時，多流道尾端會出現拖曳現象，使原本積水的區域恢復反應，性能提升。
單條蜿蜒式流道的排水效果最好，但整體性能最差；三條蜿蜒流式道電流密度區域變異大，受進氣流量影響也最明顯；平行蜿蜒式流道電流密度分佈較平均，但排水性最差。本實驗所研究的單電池，整體性能表現以平行蜿蜒式流道最好，以進氣溫度55 °C與進氣流量50 ml/min為最佳的操作條件。

關鍵字

燃料電池 ； 水管理 ； 電流密度 ； 水分佈 ； 暫態分析

並列摘要

It is well known that proper water management inside a proton exchange membrane fuel cell is essential for obtaining good performance. Insufficient water lowers the conductivity of the membrane and causes high internal resistance whereas excess water leads to flooding of the electrode and decreases reaction area. However, water management is quite difficult because it is not easy to be observed directly.
The experiment set up demonstrates a new method of measuring current distribution and water distribution in a specially designed single fuel cell, using a transparent flow field plate and segmented gold foil current collectors. Each segment was electronically insulated from the neighboring compartments. With current multiplex method, current distribution was measured by shunts connected to the corresponding segments. Furthermore, image of water formed inside the cathode and anode are presented to explain the phenomenon of water flooding in the gas channels. This approach provides a useful tool for investigating different flow field designs and for optimizing utilization of the active electrode area with the most appropriate reactant stoichiometries and humidification conditions.
The results reveal that the water distribution propagates from outlet to inlet at cathode side and dry effect propagates from inlet to outlet. Water condensed from small droplet to swelled droplet and then clogged channels. Water molecules were carried by electro-osmotic drag near inlet areas and back diffusion phenomenon is growing vigorously near outlet. High stoichiometry causes inlet area to dry out and less water holdup than operating in low stoichiometry. Performance loss occurs at elevated temperature near inlet and water condenses more easily than low temperature condition. Under less humidification conditions, segment performance increases as distance from the gas inlet increases, indicating external humidification of the hydrogen increases performance. Furthermore, back flow occurs at gas outlet of multi-channels and leads to more flooding areas that decrease the performance.
Single serpentine has a characteristic of draining out water fluid. The current density varies more steeply between neighboring area of tri-serpentine flow type. Parallel-serpentine gets better performance of these three flow type, but it’s easy to be clogged by water fluid in last two channels. The optimum operating conditions for the studied cell are around 55°C and 50 ml/min with hydrogen humidification.

並列關鍵字

Water distribution ； Fuel cell ； water management ； Current density ； Transient analysis

參考文獻

2. Scherer, G..G.., 1997, “Interfacial aspects in the development of polymer electrolyte fuel cell”, Solid State Ionics, Vol.94, pp.249-257.

3. Bevers, d., Roger., Von Bradke, M., 1996, ”Examination of the influence of PTFE coating on the properties of carbon paper in polymer electrolyte fuel cells”, Journal of Power Sources, Vol.63, pp.193-201.

4. Lee, W.K., Ho, C.H., Van Zee, J.W., and Murthy, M., 1999, ”The effects of compression and gas diffusion layers on the performance of a PEM fuel cell”, submitted to Journal of Power Sources.

5. Verbrugge, M.W. and Hill, R.F., 1990b, “Transport Phenomena in Perfluorosulfonic Acid Membranes during the Passage of Current,” Journal of Electrochemical Society, Vol.137, pp.1131-1138

6. Verbrugge, M.W. and Hill, R.F., 1990a, “Ion and Solvent Transport IN Ion-Exchange Membranes,” Journal of Electrochemical Society, Vol.137, pp.893-899.