利用點擊反應與原位聚合法製備磺酸化聚三唑/黏土奈米複合材料之燃料電池質子傳導膜與性質探討

Abstract

第一部分研究，利用修飾炔丙基官能基(Propargyl groups)的黏土(Clay)經由點擊化學(Click chemistry)，以原位聚合(In situ polymerization)的方式製備出脫層型態Polytriazole (PTA) /Clay奈米複合材料。本篇研究中，蒙脫土已成功的以脫層型態分散在高分子Polytriazole基材中，並且改善了複材的熱性質與機械性質。利用此方式也可應用在其他具炔丙基改質土與具疊氮(azide-)和炔烴基(alkyne-)的高分子聚合反應中。

近年有許多不同種類的質子交換膜(Proton exchange membrane)應用於燃料電池(Fuel cells)，其中以非含氟的高分子材料為基材之質子交換膜最被廣泛研究。經由導入高含量磺酸根於高分子，非含氟材料的質子交換膜可以達到高的質子導電度(Proton conductivity)，但此方式也同時損耗交換膜的機械性質，並且引起了甲醇穿透(Methanol crossover)的問題。此外這些聚集的磺酸根離子也將會造成質子交換膜有過度澎潤甚至溶在甲醇水溶液中。研究如何改善質子導電度且降低甲醇穿透的問題時，同時也不犧牲交換膜的機械性質和化學穩定性目前仍然具有相當大的挑戰。

第二部份研究，介紹如何利用點擊反應(Click reaction)並以原位聚合法 (In situ polymerization)製備出Sulfonated Polytriazole (SPTA) / Clay燃料電池質子傳導膜。有鑑於第一部份PTA/Clay奈米複材製備的成功，在此我們將單體1,4-bis(azidomethyl)benzene(BAB)換成具磺酸根官能基的sodium (E)-6,6'-(ethene-1,2-diyl) bis(3-azidobenzenesulfonate) (SEBA)，使複材可更多元的應用在燃料電池質子傳導膜。本篇研究中，蒙脫土也成功的以脫層型態分散在高分子基材中，不僅熱性質與機械性質提升，複材的保水性更佳、離子通道變小及離子團簇均勻分散，以上特性也使甲醇穿透度大幅下降與質子傳導度提升。只要加少量的的黏土(1-3wt%)即可有大幅性能提升。對於無機材料黏土導入的新手法，使未來在直接甲醇燃料電池(DMFC)質子傳導膜(PEM)的部分，又增加了一個很好的製備路徑。

(Part 1) This manuscript describes the preparation of polytriazole/clay nanocomposites through in situ polymerization of PTA, using click chemistry, in the presence of a propargyl-modified clay. The clay layers became exfoliated and dispersed well in the PTA matrix, thereby improving the thermal and mechanical properties of the clay. This approach can be extended to combine propargyl-modified clays with other azide- and alkyne-containing polymers.

Among various types of proton exchange membranes(PEMs) for fuel cells, several nonfluorinated polymeric materials are attracting more attention as alternatives to perfluorinated polymer membranes.The nonfluorinated PEMs can achieve high proton conductivities by introducing high extent of sulfonic acid groups, but tend to deteriorate the mechanical strength and permeability of PEMs simultaneously. The aggregation of conductive sites will cause these PEMs highly swollen or dissolved in aqueous/alcoholic solutions. The development of more efficient membranes with improved proton conductivity and reduced methanol crossover without detrimentally mechanical and chemical stabilities remains an important challenge.

(Part 2) Sulfonated polytriazole-clay (SPTA-clay) nanocomposites have been successfully prepared by in situ polymerization of SPTA using click chemistry in the presence of propargyl-functionality modified clay. The clay layers were found to be exfoliated and well dispersed in the SPTA matrix which resulted in improvement of thermal stability, echanical strength, methanol permeatbility, water retention, ion channel size, and ionic cluster distribution by the incorporation of a small amount of clay (SPTA 1 and 3). The SPTA-clay nanocomposite membranes by incorporating a small amount of clay in SPTA matrix possess higher selectivity defined as ratio of proton conductivity to methanol permeability, therefore, it had potential usage of a proton exchange membrane (PEM) for direct methanol fuel cells (DMFCs).