高溫型質子交換膜燃料電池與陰離子交換膜燃料電池，由於這兩類新型高分子電解質薄膜燃料電池有潛力解決關於電極反應效率不佳、貴重白金觸媒使用以及水管理等問題，因此近期的研究發展相當受到期待。基於(苯)咪唑官能基特殊的可酸可鹼的兩性特徵，藉由得到質子或脫去質子(質子化或去質子化)過程可轉化成為帶正價離子基或帶負價離子基，即可發展出具陽離子(質子)傳導基或者具陰離子傳導基之兩類電解質薄膜。因此，本論文聚焦於研究發展數種新型含苯咪唑官能基之燃料電池用高分子電解質薄膜，其中包含磷酸摻混之奈米複合材料薄膜、磷酸摻混之非對稱性孔洞材料薄膜、以及帶有(苯)咪唑官能基之四級胺聚苯咪唑薄膜。前兩者應用於高溫型質子交換膜燃料電池，後者應用於陰離子交換膜燃料電池。
本論文的第一部份，研究用於高溫型質子交換膜燃料電池的含有改質奈米碳管之聚苯咪唑奈米複合材料薄膜。改質奈米碳管的導入，可同時提升電解質薄膜之機械性質與燃料電池之功率。藉由非共價鍵結改質與共價鍵結改質的兩種方式來改質多壁奈米碳管，分別製備出磺酸化奈米碳管(MWNT-poly(NaSS))與咪唑化奈米碳管(MWNT-imidazole)。本研究透過紅外線光譜、X光光電子能譜、拉曼光譜與熱重分析等對改質奈米碳管進行鑑定。相較於非改質奈米碳管與磺酸化奈米碳管(MWNT-poly(NaSS))，咪唑化奈米碳管(MWNT-imidazole)對於聚苯咪唑有較好的相容性以及機械性質強化效果。含磺酸化奈米碳管之聚苯咪唑複材薄膜與含咪唑化奈米碳管之聚苯咪唑複材薄膜，在兩者之飽和磷酸含量情況下，並在160°C無水環境下所測得之質子傳導率皆高於純聚苯咪唑薄膜，分別為5.1 × 10-2 與 4.3 × 10-2 S/cm。並且，這兩類改質奈米碳管之聚苯咪唑複材薄膜在170 °C無水環境下所測得的燃料電池功率亦相對高於純聚苯咪唑薄膜。
本論文的第二部分，研究用於高溫型質子交換膜燃料電池之非對稱性孔洞聚苯咪唑薄膜。該薄膜透過軟模法成功地製備，軟模法採用一種特殊的離子液體 ([EMIM][TFSI]) 來做為軟模版或發泡劑。非對稱性孔洞聚苯咪唑薄膜，透過掃描式電子顯微鏡觀察形貌，發現其非對稱孔洞結構包含了一層緻密層與一層孔洞層。在其成膜過程中，發展非對稱結構的主要驅動因素推測來自於高分子主體與發泡劑間的密度差異。對於磷酸摻混之非對稱性孔洞聚苯咪唑薄膜，具高孔隙率之薄膜試片顯出相當高的磷酸含量與質子傳導率，磷酸摻雜程度可達到23.6，以及質子導電率可達到6.26 × 10-2 S/cm。另外，研究探討發現非對稱性孔洞聚苯咪唑薄膜，交聯處理對於提升薄膜其機械強度與氧裂解安定性有所幫助。本研究，我們製備出由含有非對稱性孔洞聚苯咪唑薄膜所構成的膜電極，並在高溫無水環境下的實際驗證燃料電池的功率表現。
論文的第三部分，合成一系列帶有(苯)咪唑嗡官能基之四級胺化聚苯咪唑薄膜，應用於陰離子交換膜燃料電池。高分子材料結構藉氫譜核磁共振、紅外線光譜與能量分散式元素分析等完成鑑定。同時，四級胺化聚苯咪唑薄膜之咪唑嗡官能化程度、離子交換能力、吸水率、膨脹率、水合數目與離子傳導率等各項性質皆進行量測分析與探討。實驗結果顯示，所合成製備的四級胺化聚苯咪唑薄膜，其離子交換能力落在0.96~1.49 mmol/g範圍之間，在80˚C所量測的最佳離子傳導率達2.72 × 10-2 S/cm。此外，四級胺化聚苯咪唑薄膜的熱安定性、機械性質與鹼安定性亦進行評估探討。實驗結果顯示，四級胺化聚苯咪唑薄膜具有可接受的熱安定性與機械強度，不過(苯)咪唑嗡官能基之鹼安定性仍須進一步改善。

This thesis focused on developing and studying polymer electrolyte membranes containing benzimidazole moiety for fuel cells. Benzimidazole is amphoteric and exists two equivalent tautomeric forms, which can be acted as either proton exchange site or anion exchange site depending on the transfer of a proton (deprotonation and protonation). Three novel polybenzimidazole (PBI) based polymer electrolyte membranes have been developed, including phosphoric acid doped MWNT/PBI composite membranes for high temperature proton exchange membrane fuel cell (HT-PEMFC), phosphoric acid doped asymmetric PBI membranes for HT-PEMFC, and quaternized PBI membranes with imidazolium and benzimidazolium functional groups for anion exchange membrane fuel cell (AEMFC). HT-PEMFC and AEMFC are the two promising variants of the polymer electrolyte membrane fuel cell, which have possibilities to meet the challenges associated with electrode reaction kinetics, use of expensive Pt catalyst, and water management.
Firstly, composite membranes used for proton exchange membrane fuel cells comprising of PBI and carbon nanotubes with certain functional groups were studied. They could enhance both the mechanical property and fuel cell performance at the same time. Two kinds of composite membranes including sodium poly(4-styrene sulfonate) functionalized multiwalled carbon nanotubes (MWNT-poly(NaSS))/ PBI and imidazole functionalized multiwalled carbon nanotubes (MWNT-imidazole)/PBI composite membranes were prepared. The functionalization of carbon nanotubes involving non-covalent modification and covalent modification were confirmed by FITR, XPS, Raman spectroscopy, and TGA. Compared to unmodified MWNTs and MWNT-poly(NaSS), MWNT-imidazole provided more significant mechanical reinforcement due to its better compatibility with PBI. For MWNT-poly(NaSS)/PBI and MWNT-imidazole/PBI composite membranes at their saturated doping levels, the proton conductivities were up to 5.1 × 10-2 and 4.3 × 10-2 S/cm at 160°C under anhydrous condition respectively, which were slightly higher than pristine PBI (2.8 × 10-2 S/cm). Also, MWNT-poly(NaSS)/PBI and MWNT-imidazole/PBI composite membranes showed relatively improved fuel cell performance at 170 °C compared to pristine PBI.
Secondly, a novel asymmetric PBI membrane used for HT-PEMFC has been successfully fabricated by a soft-template method using ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) as porogen. The asymmetric PBI membrane typically exhibits a double layer structure comprising a dense layer and a porous layer with a distinguishable boundary. The morphology and asymmetry of the porous structure has been characterized by SEM micrographs. The density difference between the polymer matrix and the porogen can be considered as the driving force for developing the asymmetrical structure. The phosphoric acid-doped asymmetric PBI with a high porosity exhibited considerably enhanced doping level and proton conductivity. For example, a doping level of up to 23.6 and a proton conductivity as high as 6.26 × 10-2 S/cm were achieved. Moreover, the crosslinking modification of asymmetric PBIs had facilitating effects on mechanical strength and oxidative stability, which were investigated. We have also demonstrated fuel cell performance of membrane electrode assembly (MEA) based on the asymmetric PBI at elevated temperatures under anhydrous conditions in the present work.
Thirdly, a new series of quaternized PBIs having imidazolium moieties in the main-chain and/or in the side group were synthesized for use as anion exchange membrane (AEM) for fuel cells. The polymer structures were characterized by 1H NMR, FTIR, and EDX analyses. The degree of imidazolium functionalization (DIF) of the quaternized PBI was also determined. The properties required for AEM, such as ion exchange capacity (IEC), water uptake, swelling ratio, hydrated number, and ionic conductivity were measured. The IECs of the quaternized PBIs were in the range of 0.96~1.49 mmol/g. The highest ionic conductivity of 2.72 × 10-2 S/cm was achieved at 80˚C. Besides, the thermal stability, mechanical properties, and alkaline stability of the quaternized PBI membranes were investigated. The results revealed that the thermal stability and mechanical properties of the membranes were acceptable, but the alkaline stability of the (benz)imidazolium moieties needs to be improved.

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