應用金屬薄片雙極板於質子交換膜燃料電池之研究

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Title:	應用金屬薄片雙極板於質子交換膜燃料電池之研究 Application of Metallic Thin Bipolar Plates on a Proton Exchange Membrane Fuel Cell
Authors:	蘇聖惇
Contributors:	機械工程學系數位機電碩士班
Keywords:	高溫型質子交換膜燃料電池金屬雙極板性能測試電化學阻抗電化學阻抗
Date:	2017
Issue Date:	2017-04-07 11:16:47 (UTC+8)
Abstract:	質子交換膜燃料電池有著低噪音、低污染與發電轉換效率高、方便移動、啟動關閉迅速與運作溫度低的優點，對於運輸工具與可攜式能源是一項非常優良的選擇。雙極板在質子交換膜燃料電池整體成本與重量中占據了很大的比例，使用金屬薄片雙極板取代傳統石墨雙極板即能夠有效達到輕量化與降低成本的效果。另一方面，改用高溫型質子交換膜燃料電池可解決低溫型燃料電池水管理不易、一氧化碳之容忍度較差、觸媒使用量較大等缺點。因此，金屬薄片雙極板與高溫型質子交換膜燃料電池具有相當好的發展潛力。本研究以自製墊片搭配不鏽鋼SS304、SS316沖壓製成的金屬雙極板，成功地組裝單電池並進行低溫與高溫兩個部分的實驗。預計在改善墊片製程後，使用金屬薄片雙極板取代傳統石墨板，雙極板重量將由127.26 g減輕至約80 g，減少約37%，且電池可獲得更佳的耐震效果。本研究所整合之高溫型PBI/H3PO4質子交換膜燃料電池最大功率密度可達250 mW cm-2。低溫型質子交換膜燃料電池最大功率密度可達223 mW cm-2。本研究實驗結果發現，氣密性能與組裝扭矩有著正向關係，在使用組裝扭矩為7.0 N-m時皆可獲得最佳的氣壓下降速率。在墊片材質方面，由於耐溫矽氧樹脂在160 oC環境下之物理特性較穩定，故較RTV矽氧樹脂更適合用於高溫型質子交換膜燃料電池。使用低溫型質子交換膜時，由於歐姆阻抗隨扭矩增加而下降，因此性能隨著扭矩上升而增加。但當扭矩超過7.0 N-m時，會因氣體擴散層孔隙率下降、微孔層之破壞造成排水不易以及流道變形，最後導致質傳阻抗上升，造成性能下降，而此現象於高電流時更為明顯。在使用高溫型質子交換膜時，SS316雙極板與SS304雙極板之性能皆未隨著扭矩的上升出現明顯的變化。由阻抗分析可得知，此乃因歐姆阻抗以及電荷轉移阻抗與質傳阻抗之總和未隨扭矩變化而明顯變化，此乃因高溫矽氧樹脂墊片硬度較高所致。 Proton exchange membrane fuel cells have the advantages of low noise, low pollution level, high efficiency, high mobility, rapid start-up, and low operating temperature. It is a good candidate for transportation and portable power systems. Bipolar plates occupy a large proportion of cost and weight of a proton exchange membrane fuel cell. Using thin metallic bipolar plates to replace the traditional graphite bipolar plates in the proton exchange membrane fuel cell can effectively reduce the volume, weight and cost of the fuel cell. Additionally, using a high temperature proton exchange membrane fuel cell can solve the problems of difficult water management, weak carbon monoxide tolerance and high catalyst loading in a low temperature fuel cell. As a result, the development of thin metallic bipolar plates and the high temperature proton exchange membrane fuel cell is promising. In this study, we successfully assembled the single cells with the self-made gaskets and the thin metallic bipolar plates made of 304 and 316 stainless steel, which were manufactured by stamping processes. We as well carried out two parts of experiment, the low temperature fuel cell and the high temperature fuel cell. After we modify the manufacture process of the gasket, it is expected that weight of a bipolar plate will decrease from 127.26 g to about 80 g, i.e., a 37% reduction, as using the thin metallic bipolar plates to replace the traditional graphite bipolar plates. Furthermore, the fuel cell with the thin metallic bipolar plates is expected to have a better shock resistance. In this study, the maximum power density of the high temperature PBI/H3PO4 proton exchange membrane fuel cell integrated with the metallic bipolar plates is 250 mW cm-2. The maximum power density of the low temperature proton exchange membrane fuel cell integrated with the metallic bipolar plates is 223 mW cm-2. The experimental results indicate that the rate of pressure drop decreases with increasing the assembly torque. At the torque of 7.0 N-m, the best pressure drop rate is obtained. In the aspect of the gasket material, the temperature-resistant silicone gasket is more suitable for high-temperature proton exchange membrane fuel cells than the RTV silicon gasket because the physical properties of the temperature-resistant silicone are more stable than the RTV silicon at 160 oC. Increasing the torque increases the performance of the low temperature fuel cell using because the ohmic resistance decreases with increasing the torque. Nevertheless, the fuel cell performance tends to decrease when the torque exceeds 7.0 N-m. It may be attributed to the damaged micro-porous layer or declined porosity of gas diffusion layers, resulting in an elevated mass transport resistance. This phenomenon is more obvious at high currents. The performance of the fuel cell using SS316 bipolar and SS304 bipolar are both not improved significantly by increasing the torque for the high temperature fuel cell. This is because the ohmic resistance and the sum of the charge transfer resistance and the mass transport resistance do not change significantly with the change in torque. This is because of a higher hardness of the temperature-resistant silicone gasket.
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