聚(2,5-苯並咪唑)與官能基化氧化石墨烯之複合材料應用於中高溫質子交換薄膜

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题名:	聚(2,5-苯並咪唑)與官能基化氧化石墨烯之複合材料應用於中高溫質子交換薄膜
作者:	張楷杰;CHANG, KAI-CHIEH
贡献者:	化學學系
关键词:	燃料電池;高溫質子交換薄膜
日期:	2020-07-01
上传时间:	2020-09-02 15:04:20 (UTC+8)
出版者:	國立中央大學
摘要:	與傳統質子交換膜燃料電池相比高溫型質子交換膜燃料電池擁有較快的電化學反應速度、較高的一氧化碳耐受度和不需要複雜的水管理等優點。能展現優越高溫型燃料電池特點最關鍵的元件是質子交換膜。為使電池能發揮較好效能一個良好的高溫型質子交換薄膜，除了必須具備高質子導電度之外還需要具備化學穩定性和一定程度的機械強度使其能延長使用壽命。目前較常使用的在高溫型質子交換膜材料為PBI (polybenzimidazole)高分子材料，此種材料雖然具有很高的磷酸摻雜水平，但在高度吸附磷酸之後會導致其機械強度的下降，除此之外，此材料成本昂貴不利於廣泛使用，因此開發一種在高溫環境下仍具有良好的質子導電度、化學穩定性和機械強度的質子交換薄膜是許多學者的研究目標。本研究選用聚2,5-苯並咪唑(ABPBI)高分子，此種材料比起PBI成本較低且合成方法簡單，只需要一種單體且一聚合步驟即可完成。因其具有鹼性的苯並咪唑(benzimidazole)結構，具備耐高溫和良好磷酸的摻雜能力，因此ABPBI可以與磷酸產生酸鹼作用力，使ABPBI擁有吸附磷酸的能力。此類高溫型燃料電池薄膜即以磷酸做為質子傳遞的介質。為改善物性本研究選用了官能基化氧化石墨烯(graphene oxide) 作為添加物。該添加物乃在為氧化石墨烯的結構接上苯並咪唑(benzimidazole)官能基團。以這樣設計的官能基化石墨烯的目的一方面是提高氧化石墨烯的分散性，另一方面可以用於吸附更多的磷酸，提高薄膜磷酸的摻雜量，增加薄膜導電度。氧化石墨烯結構上的含氧官能基團(如：羥基、羧基)也可以在薄膜體系中提供更有效的新穎質子傳遞通道，進一步的提高薄膜的質子導電度。為更進一步改善導電及機械物性，我們依據本實驗室先前研究的方法以外加電場誘導產生具有順向排列紋理之隔離膜。薄膜中的孔道形成具有方向性的優先取向結構，提供更直接的質子傳遞路徑，增加薄膜傳遞質子的效率。以添加2 wt%的官能基化氧化石墨烯的薄膜(ABPBI-2)為例薄膜經過外加電場誘導後，質子導電度達到0.063 S/cm；相較於原始的ABPBI薄膜導電度提升了大約3倍。氧化石墨烯具有的含氧官能基會與磷酸形成氫鍵，提高薄膜保存磷酸的能力，避免薄膜在高溫操作下造成磷酸的流失，磷酸流失率從28%減少至10%，在高溫下有較好的質子導電度穩定性。另外在化學穩定性方面，官能基化的氧化石墨烯與ABPBI高分子之間的氫鍵可以增加薄膜分子間作用力，使薄膜的化學穩定性提高了約20%，延長薄膜的使用壽命。 ;High-temperature proton exchange membrane fuel cell have many advantages, such as a simple water and cooling system, higher catalytic activity and enhanced tolerance to carbon monoxide. An excellent high-temperature proton exchange membrane must have high electrical conductivity, chemical stability and mechanical strength. The most commonly used material for high-temperature proton exchange membranes is PBI (polybenzimidazole). Although the material has a very high level of phosphoric acid doping, it will lead to a decrease in the mechanical strength after highly adsorbed phosphoric acid. In addition, this material is expensive not suitable for widespread use. Therefore, the development of proton exchange membranes with good proton conductivity, chemical stability and mechanical strength under high temperature environment is the research goal of many scholars. In this study, we use ABPBI polymer, which is cheaper than PBI and simple in synthesis. ABPBI has an imidazole functional group that can adsorb phosphoric acid. Acid−base pairs composed of imidazole and phosphoric acid can realize proton conductivity. In addition, we chose graphene oxide as an additive. The graphene oxide is functionalized to connect the benzimidazole functional group. The purpose of the functionalization is to increase the dispersibility of graphene oxide and adsorb more phosphoric acid to increase the membrane conductivity. The optimal content of functionalized graphite oxide is 2 wt % (ABPBI-2 membrane). By applying an external electric field create a preferential orientation structure with directionality. This structure forms a more direct proton transfer path and increases the efficiency of the membrane to transfer protons. The proton conductivity of APBBI-2 membrane reaches 0.063 S/cm which are 3 times higher than the original ABPBI membrane. The oxygen contained functional group of graphene oxide forms a hydrogen bond with phosphoric acid, which increases the ability of the membrane to retain phosphoric acid. The phosphoric acid loss rate is reduced from 28% to 10%. In addition, the hydrogen bonding force between the functionalized graphene oxide and the ABPBI polymer can increase the intermolecular force which improve the chemical stability for 20%.
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