| 摘要: | 本論文採用熱壓製程製備膜電極組(Membrane Electrode Ass- embly, MEA)，所得MEA先用I-V極化曲線分析該電池之性能。然而，由於MEA之壓降損失不能由極化曲線理解其理由，因此本實驗進一步配合交流頻譜(Electrochemical Impedance Spectroscopy ,EIS) 分析探討電池內部結構各組成單元接觸面之特性。 EIS結果顯示：熱壓製程之溫度、壓力、質子交換膜之厚度與Nafion溶液之負載均影響MEA的性能甚鉅。膜電極組熱壓之最佳溫度為125℃，若溫度<125℃，則質子交換膜與觸媒顆粒黏合不夠緊密；反之，若溫度>125℃，則造成觸媒顆粒被質子交換膜過度被覆而失去活性。另一方面，膜電極組熱壓之最佳壓力為50kg/cm2，若壓力<50kg/cm2，其接觸電阻太高；反之，若壓力>50kg/cm2，造成質子交換膜與觸媒顆粒間接觸壓合之效果不佳。使用厚度不同之Nafion質子交換膜組成MEA時，以最薄的50.8um(Nafion112)，其阻抗最低；而以最厚的177.8um(Nafion117)，其阻抗值最高，電化學阻抗的高低，主要取決於質子交換傳輸路徑的長短，與催化反應的難易而定。Nafion溶液最佳負載量為1.0mg/cm2，若負載量太少則質子傳導所需網絡不足；若負載過量則觸媒與氣體燃料接觸面積太少，無法進行催化反應。 MEA之最佳操作溫度為60℃；若溫度太低，質傳擴散作用不足，電極反應速率降低；若溫度太高，則造成觸媒迅速老化而降低電極反應速率。 MEA之最佳氣體燃料進給量(陽極/陰極化學計量比為1.5：2.0)，當陰極端計量比減小時，則造成氣體燃料供給不足；而當計量比增大時，則造成氣體燃料與催化劑的接觸時間不足，兩者均不利於MEA的有效操作。 The paper will use hot press process to produce Membrane Electrode Assembly (MEA), and used I-V polarization curve to analyze the performance of the cell. However, the voltage loss of the MEA can not to explain from polarization curve, therefore the experiment to go a step further used Electrochemical Impedance Spectroscopy (EIS), and analyze the characteristic of contact interface of every component inside cell structure. Result of EIS to exhibit: the temperature and pressure of hot press process, and the thickness of proton exchange membrane, and the load of Nafion solution that have more effect of MEA performance. The best hot press temperature is 125℃ in MEA, if the temperature<125℃,then proton exchange membrane and catalyst particle can not bonding enough. On the other hand if the temperature>125℃, then catalyst particle will to warp by proton exchange membrane and to lose activity. On the other hand, the best hot press pressure is 50kgf/cm2 in MEA, if the pressure<50kgf/cm2, then the contract resistance is so high. On the other hand if the pressure>50kgf/cm2, then to cause between proton exchange membrane and catalyst particle bonding result not fine. Use proton exchange membrane of different thickness to compose MEA, when 50.8um (Nafion112) that is most thin and impedance is lowest, and 177.8um (Nafion117) that is most thick and impedance is highest. The electrochemical impedance value that major to depend on proton exchange transmission path is long or short, and catalytic reaction is good or bad to decide. The best Nafion solution load quantity is 1.0mg/cm2. If the load quantity is too less, then proton exchange transmission network is not enough. If the load quantity is too much, then the contract area that between catalyst and gas fuel is too less and can not to proceed catalytic reaction. The best operation temperature is 60℃ in MEA. If the temperature is lowest, then the effect of mass transmission and diffusion is not enough, and electrode reaction rate is to reduce. If the temperature is highest, then to cause catalyst ageing quickly, furthermore reduce electrode reaction rate. The best gas fuel feed quantity (anode/cathode chemical stoichiometry is 1.5:2.0). When the stoichiometry is reduce in cathode that to cause gas fuel feed is not enough. When the stoichiometry is to increase that to cause the contract time of between gas fuel feed and catalyst are not enough. Both of above condition are not effective operation for MEA. |
