| 摘要: | 為了讓質子交換膜燃料電池(proton exchange membrane fuel cell, 簡稱PEMFC)達到最好的性能，適當的水管理是一個很重要的課題。一方面得即時將化學反應產生的水移除，否則產生的水會阻塞催化層與氣體擴散層，進而阻塞氧氣與氫氣的傳輸，產生高的質傳阻抗，另外一方面，離子傳導膜也需要水來進行水合作用來增加離子傳導。所以水管理與質傳效應是重大影響PEMFC性能之兩大因素。 對於PEMFC之氣體擴散層(gas diffusion layer, 簡稱GDL)，其組成包含了由碳黑與PTFE混合而成之微孔層(micro-porous layer, 簡稱MPL)以及較大孔隙之碳紙。氣體擴散層不僅用來支撐催化層，它也提供電極與流道板之間電的接觸傳遞。 即使GDL在提升PEMFC性能中扮演著一個很重要的角色，可是對於GDL跟電池內部之間的相互影響關係，卻是無法有一個相當程度的了解。在本論文係探討GDL與MPL之孔隙大小、孔隙分布、親疏水性、氣體滲透率、AC阻抗及其對於電池性能之影響。 在本研究中，MPL所使用之碳黑為乙炔碳黑(Acetylene-black)，其中實驗包含了改變PTFE loading、使用不同的碳紙厚度以及MPL厚度。所使用的碳紙為未疏水之TGPH-060、TGPH-090以及TGPH-120的商用碳紙。根據實驗結果，我們發現使用未疏水之TGPH-090，並塗佈70μm之MPL，可以得到好的水管理與電池性能，特別一點的就是在中間區域之電流密度下，使用70μm厚度之MPL有較低的電子傳遞阻抗，而且在高電流密度下，也可以減少質傳阻抗。 Water management is an important issue in order to achieve high performance of proton-exchange membrane (PEM) fuel cell. On the one hand the product water from the chemical reaction needs to be removed in time, or it may block the pores in the catalyst layers as well as the gas diffusion layer (GDL) and then hinders the transport of oxygen and hydrogen, resulting in higher mass transport resistance. On the other hand, water is needed to hydrate the ionically-conducting membrane. So water management and mass transport have been shown to be important factors these strongly influence PEMFC Performance. The GDL in a PEMFC consists of a micro-porous layer (MPL) of carbon black mixed with polytetrafluoroethylene (PTFE) that is coated onto a sheet of macro-porous carbon backing paper. This GDL not only provides physical micro-porous support for catalyst layer but also provides electrical contact between the electrode and the flow field plate. At the same time, it must allow the water formed on the cathode to exit to the gas channels and permit the passage of water between the gas streams and the membrane surface. Although the GDL is a seemingly minor component in a fuel cell, it has been shown that altering the composition of the diffusion layer can lead to substantial improvements in the performance of the cell. Though the GDL in a PEMFC plays a critical role in the rise of performance, the GDL remains poorly understood because of a lack interactive effects with the other two main repeating units, the catalyst-coated membrane and the bipolar plate. It is the purpose of the present proposal to conduct a detailed study to investigate the effects of the characteristics of the GDL and MPL, including pore size, pore distribution, hydrophobic and hydrophilic treatment, gas permeability, and AC resistance and capillary force, on the water management and performance of a PEM fuel cell. In the experiments, we used acetylene-black in MPL. The investigations include the effects of PTFE loading, carbon paper thicknesses and MPL thicknesses. The GDL used are commercial carbon papers: TGPH-060-no proofed, TGPH-090-no proofed, and TGPH-120- no proofed. According to our results, The TGPH-090-no proofed coated with 70μm MPL provides the best water management and performance in the PEMFC. Especially in the middle current density region, we find that when the thickness of MPL is 70μm, the cell has the lowest charge resistance. It also reduces the resistance of mass transport in the high current density region. |
