磺酸化苯乙烯-乙烯/丁烯-苯乙烯嵌段共聚合物之交聯質子交換膜

Crosslinked Sulfonated Polystyrene-block-poly（ethylene-ran-butylene）-block-polystyrene as Proton Exchange Membrane

王誌亭(Chih-Ting Wang)

指導教授 ： 趙基揚

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.01986

摘要

本論文主要目的是製備磺酸化sulfonated poly ( styrene – block - (ethylene – ran - butylene) – block - styrene) (sSEBS)交聯質子傳導膜，研究交聯後質子交換膜的性質和微結構，以期應用於氫氧燃料電池或是甲醇燃料電池。
本論文分二部分：第一部份是以不同醇官能基數目的一級醇作為交聯劑，第二部分為合成具磺酸根的一級醇作為交聯劑。交聯的形成是利用在高溫熱處理時sSEBS的磺酸根會和交聯劑的醇基進行脫水形成磺酸酯鍵結。此二部分合成的交聯膜將對微結構、熱穏定性、機械強度、耐化學性和質子傳導性質等依交聯劑添加量的不同作系統性的研究。
在第一部分我們以glycerol， D-mannitol 和poly vinyl alcohol ( PVA )此三種具不同數目醇基的交聯劑作比較。前二者可分類為小分子的交聯劑，PVA則是以高分子型態進行掍摻交聯。在加入以上交聯劑後的sSEBS交聯膜顯現出熱穏定性、機械強度的提升；耐化學性則是依具化學結構和交聯劑的添加量而改變。微結構的觀察裡，glycerol和mannitol 交聯的質子交換膜和初始sSEBS膜具有相同的微結構，並不會受到交聯劑添加量多寡的影響。但PVA交聯膜則是在PVA添加到一定量以上時開始有微結構的變形。離子交換容率和質子傳導度則是由於交聯時犧牲磺酸根，故隨著交聯劑的添加而減少，PVA交聯膜在此方面的影響尤其顯著。甲醇滲透率則是隨著glycerol和PVA的添加而能有效下降，但mannitol則是顯出上升的趨勢。變溫變濕試驗顯示交聯後的sSEBS薄膜有著質子傳導度的提升，特別是在低濕狀態中，可能原因為交聯後的結構具有保水性和交聯劑的醇基也提供了部份保水性。質子傳導度則是出現較複雜的趨勢，此可能和交聯劑分子大小、交聯後的結構與交聯劑添加量有關。
第二部份我們合成具磺酸根的苯環交聯劑，離子交換容率和質子傳導度並沒有隨著交聯劑的摻入量增加而降低，代表交聯劑上的磺酸根的確可補償sSEBS因為交聯所失去的磺酸根。另外此交聯膜在阻擋甲醇滲透和耐化學性方面皆比未交聯的sSEBS膜好。

關鍵字

燃料電池 ； 質子交換膜 ； 交聯 ； 團鍊共聚高分子 ； sSEBS

並列摘要

The major purposes of this thesis are to prepare crosslinked sulfonated poly(styrene-block-(ethylene-ran-butylene)-block-styrene) (sSEBS) membranes as the proton conducting membranes for proton exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) as well as to investigate the properties and the microstructure of the crosslinked membranes. Two parts of studies are presented using non-sulfonated (Part I) or sulfonated (Part II) multi-functional alcohols as crosslinkers. Crosslinking occurs within the sulfonated polystyrene (sPS) domains through the formation of sulfonate esters between the hydroxyl groups of the crosslinkers and the sulfonic acids of sPS via thermal curing. In each part, the dependence of transport properties, thermal stability, mechanical strength, chemical stability and morphology of the membrane on the chemical structure and the loading amount of the crosslinkers are systematically studied.
In the first part, the crosslinkers with different number of hydroxyl groups, including glycerol, D-mannitol and poly(vinyl alcohol) ( PVA ). The first two alcohols are classified as low molecular weight crosslinkers and PVA is classified as polymeric crosslinker.The introduction of these crosslinkers is demonstrated to improve the thermal stability, mechanical strengths and chemical stability and the enhancements are found to relate to the chemical structure and the loading amount of the crosslinkers. The microstructure of the crosslinked membranes are similar to that of the prisitine sSEBS membrane when glycerol and mannitol are used regardless the loading amount while the addition of PVA with high loading amount alters the microstructure. Ion exchange capacity and proton conductivity decrease with increasing loading of crosslinkers due to the loss of sulfonic acids to form crosslinking and the use of PVA leads to the most significant decrease comparing with pristine sSEBS. The use of glycerol and PVA provide the crosslinked membranes suppressed methanol crossover and improved selectivity. The crosslinked membranes also show much improved proton conductivity at elevated temperature and low relative humidity, probably owing to the better water retention within the membrane attributed to the presence of crosslinks and the hydroxyl groups of the crosslinkers. All the transport properties show complicated trends against the chemical structure and the loading amount of the crosslinkers.
In the second part, a novel bifunctinoal alcohol containing two sulfonic acids is designed and synthesized as the crosslinker. Interestingly, IEC and proton conductivity of the corresponding crosslinked membrane are almost constants regardless the loading amount of the crosslinkers, indicating the use of this novel crosslinker could compensate the loss of sulfonic acids originating from the crosslinking. The resulted membranes also exhibit lower methanol permeability and enhanced selectivity. In addition, these membranes also show improved chemical resistance comparing with pristine sSEBS.

並列關鍵字

fuel cell ； proton exchange membrane ； crosslink ； block copolymer ； sSEBS

參考文獻

1. Gebel, G., Structural evolution of water swollen perfluorosulfonated ionomers from dry membrane to solution. Polymer 2000, 41 (15), 5829-5838.

2. Weiss, R. A.; Sen, A.; Pottick, L. A.; Willis, C. L., Block Copolymer Ionomers .2. Viscoelastic and Mechanical-Properties of Sulfonated Poly(Styrene-Ethylene Butylene-Styrene). Polymer 1991, 32 (15), 2785-2792.

3. H. -G. Haubold; Th. Vad; Jungbluth, H.; Hiller, P., Nano structure of NAFION: a SAXS study Electrochim Acta 2001, 46 (10-11), 1559-1563.

4. Gierke, T. D.; Munn, G. E.; Wilson, F. C., The morphology in nafion perfluorinated membrane products, as determined by wide- and small-angle x-ray studies. Journal of Polymer Science: Polymer Physics Edition 1981, 19 (11), 1687-1704.

7. Kreuer, K.-D.; Rabenau, A.; Weppner, W., Vehicle Mechanism, A New Model for the Interpretation of the Conductivity of Fast Proton Conductors. Angewandte Chemie International Edition in English 1982, 21 (3), 208-209.