近年來，鹼性燃料電池的發展受到各界矚目，因其使用非白金觸媒，而能降低出售價格。良好的鹼性燃料電池薄膜需要高離子傳導率及低燃料竄透，但要同時兼具兩者成為鹼性燃料電池作為商業材料的阻礙之一。 本研究將高分岐結構的改質雙馬來醯亞胺聚合物(mBMI)與聚(4-乙烯吡啶) (P4VP)透過氫鍵作用力與酸鹼作用力而形成semi-IPN (半互穿網路)結構。透過mBMI帶有鹼基的官能基將水分子與氫氧根離子保留於複合薄膜中，以協助離子傳導，因此隨著mBMI添加含量增加，離子傳導度隨之上升；此外，因高分歧結構的mBMI與P4VP形成緻密結構，使複合薄膜在吸附高含量的水分的期間保有極佳的尺寸穩定性。另外，semi-IPN結構也能有效阻絕燃料竄透，因而提高電池整體的效能。 為進一步改善複合薄膜之物性，本研究以外加電場極化方式成膜，使薄膜內電負度較大的原子(如：N、O等)或具有共振性質的結構(如：苯環等)暴露於外以增加親水性，同時形成有序的親水傳導通道使非結晶區變得更加緻密。相較於無電場極化下的複合薄膜，外加電場誘導的複合薄膜展現較優越的離子傳導率(1.33×10-2~1.85×10-2 S/cm)以及低乙醇竄透率(6.15×10-8~4.02×10-8 cm2/s)，同時也有效提高薄膜選擇率。 本研究顯示以外加電場誘導方式製備複合薄膜，不僅能提升離子傳導度、降低燃料竄透率等特性之外，在物性的方面也有增長，像是提高複合薄膜的化學穩定性、熱穩定性以及機械強度等，在最後的ADEFC單電池測試中，其電流密度為 112 mA/cm2時，具有最大功率密度為 13.66 mW/cm2，顯示此類型複合薄膜可應用於鹼性直接乙醇燃料電池中。 ;Being able to use non-platinum based catalyst which promises substantial fuel cell cost reduction, alkaline fuel cell received growing interests especially in the development of key fuel cell materials. Previous attempts to develop alkaline ionic exchange membrane encounter the dilemma that factors to enhance one of the cardinal properties: conductivity, low ethanol permeability, and mechanical/chemical stability are usually achieved at the expanse of the rest. This situation constitutes the major hindrance to rapid commercialization of alkaline fuel cell. In this study, we report a novel approach in preparing fuel cell membrane based on the composite system of poly(4-vinylpyridine) (P4VP) polymer reinforced by bismaleimide (mBMI) hyper-branch oligomer. P4VP and mBMI form miscible blends through intermolecular hydrogen bonding between –NH (mBMI) and –N (P4VP). This composite shows high ionic conductivity because the hyper-branched oligomer served both to institute mechanical/chemical stability, but the specific functional groups also promotes OH- transport and repels alcohol due to its huge solubility parameters difference from that of alcohol. As a result, the composite membrane exhibited simultaneous increase of both the ionic conductivity; a pronounced reduction of alcohol permeability and enhanced membrane strength. Most interestingly, preparing membrane under externally applied electric field (E-F poling) initiated changes in the membrane morphology that leads to further improvement of these physical properties. The physical, chemical and electronic properties of the two series of P4VP / mBMI membranes with and without electric field-induced composite membranes are compared through Alkaline stability, Fenton test, TGA and XRD analyses. The results confirmed membrane prepared under applying external electric field displayed high ionic conductivity; low fuel permeation; high mechanical strength and high chemical stability. After E-F poling, the composite membrane displays ionic conductivity of (1.33×10-2 ~ 1.85×10-2 S/cm) and low ethanol permeation (6.15×10-8 ~ 4.02×10-8 cm2/s); yielding record high ethanol selectivity ratio ( > 4.60×105 S s cm-3). The maximum power density reach up to 13.66 mW/cm2 with a current density at 112 mA/cm2. This improvement is attributed first to the entangled P4VP with mBMI chain and the realignment of the twisted helical segment under external electric field which induced more ordered ion conducting channel, tougher membrane strength and dense polymer chain packing. As results of these structure attributes, fuel cell membrane bearing high ion conductivity; low fuel permeation; high membrane strength; and high chemical stability can be established, simultaneously.
