含浸磺酸化聚苯乙烯之聚四氟乙烯膜於燃料電池質子交換膜之應用

Sulfonated Polystyrene Impregnated Poly(tetrafluoroethylene) Membrane as Proton Exchange Membranes for the Application in Fuel Cell

李維倫(Wei-Luen Lee)

指導教授 ： 孫一明

元智大學/工程學院/化學工程與材料科學學系/碩士(2002年)

摘要

本研究利用多孔性聚四氟乙烯(PTFE)薄膜為基材，以Ar/H2電漿處理方式使其膜表面與孔洞壁表面活化，再浸入含離子交換性磺酸官能基(SO3─)之磺酸化聚苯乙烯(SaPS)溶液中進行披覆處理，經乾燥處理程序後得到可使用於燃料電池系統中之質子交換膜。本研究中所使用的鑑定方法包括薄膜離子導電度分析、薄膜結構電顯觀察與元素分析、官能基分析、薄膜結晶性、薄膜機械強度、水與甲醇的膨潤性、氣體滲透性、化學與熱穩定性等測試的方法，並與商業化之Nafion-117膜作比較，以驗證其應用於燃料電池高分子電解質中之電極膜組的可行性。
原初PTFE膜對純水接觸角度為141 ±4°，而經電漿處理後接觸角度降為102 ±5°，證明電漿處理程序的確會改善PTFE薄膜表面親水程度；而由掃描式電子顯微鏡(SEM)與FTIR-microscopy可觀察到電漿處理後之PTFE膜的確會有SaPS披覆於上。由氣體滲透實驗結果，PTFE-SaPS膜於O2與H2滲透係數比Nafion-117膜低許多，有可能降低燃料電池系統中氣體未反應前溢透過質子交換膜的程度。
一般而言，離子導電度可隨膜材含水率與溫度增加而提高，而磺酸化程度(離子交換容量)愈高則離子導電度也愈高，若利用交流阻抗(AC Impedance)儀分析膜材離子導電度，於相對溼度為35 ％ 時，離子導電度接近1.0 ×10-3 S/cm，略低於Nafion-117膜(σ＝5.7 ×10-3 S/cm)；由膜材離子交換容量與吸水膨潤性可知PTFE-SaPS膜皆優於Nafion-117膜，因此於環境相對溼度為95 ％時，PTFE-SaPS 60膜離子導電度可接近1.0 ×10-2 S/cm左右，高於Nafion-117膜之6.4 ×10-3 S/cm。由以上幾種結果可以判斷，PTFE-SaPS膜的確有應用於燃料電池上質子交換膜的可行性。

關鍵字

聚四氟乙烯 ； 電漿 ； 磺酸官能基 ； 聚苯乙烯 ； 燃料電池 ； 質子交換膜 ； 膜電極組 ； 離子導電度

並列摘要

In this study, porous poly(tetrafluoroethylene) (PTFE) membranes were treated with Ar/H2 plasma to enhance their surface activity, and then impregnated with sulfonated atactic polystyrene (SaPS). The obtained membranes were tested for the application as proton exchange membranes (PEM) in fuel cell. A series of standard characterization methods were used to identify the membrane properties, such as FIIR-ATR/microscopy, SEM observation, EDX, density measurements, thermal analysis, mechanical test, swelling test in water and in methanol, chemical stability, gas permeability, and AC impedance analysis. The properties of PTFE-SaPS membranes were compared with those of Nafion-117 with an aim to be used for the fabrication of membrane electrode assembly (MEA).
After plasma treatment, the hydrophilicity of the membrane surface was improved as the water contact angle of the membrane dropped from 141 ±4° to 102 ±5°. FTIR-microscopy and SEM observation confirmed the impregnation of the sulfonated polystyrene on the surface as well as in the inner pores of the membranes. The permeabilities of oxygen and hydrogen through the PTFE-SaPS membranes were one to two orders lower than those through Nafion-117 membranes.
The ion conductivity of the PTFE-SaPS increased as temperature, humidity, and ion-exchange capacity (degree of sulfonation) and degree of swelling of the membranes. When the humidity was 35 %, the ion conductivity of PTFE-SaPS membranes was close to 1.0×10-3 s/cm and it was lower than that of Nafion-117 membrane (σ＝5.7×10-3 S/cm). At 95 % humidity, the ion conductivity of PTFE-SaPS (σ＝1.0 ×10-2 S/cm) was better than Nafion-117 membrane (σ＝6.4×10-3 S/cm). Based on all the data, PTFE-SaPS membranes have potential to be used for PEMFC.

並列關鍵字

PTFE ； plasma ； sulfonated ； polystyrene ； fuel cell ； PEM ； MEA ； ion conductivity