- 學位論文
聚電解質多層膜於直接甲醇燃料電池 質子交換膜製備之應用
Polyelectrolyte Multilayer Membranes for the Preparation of Proton Exchange Membranes in Direct Methanol Fuel Cells
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摘要
本研究利用逐步靜電吸附技術 (LBLESA) 改質Nafion-117膜材表面，以應用於甲醇燃料電池中之質子交換膜。膜材表面藉由靜電吸引力吸附上陽離子聚電解質聚丙烯胺溴化氫poly(allyamine hydrochloride) (PAH)與陰離子聚電解質聚丙烯酸poly(acrylic acid) (PAA)形成多層聚電解質層。本研究所使用的鑑定方法包含全反射紅外光光譜分析、接觸角實驗、X光光電子能譜分析、穿透式電子顯微鏡觀測、原子力顯微鏡觀測、水的膨潤性測試、甲醇水溶液的滲透蒸發實驗與質子傳導率分析等測試方法，並與未改質前之膜材作比較，以驗證其應用於甲醇燃料電池高分子電解質中之電極膜組的可行性。 陰陽聚電解質層對水之接觸角有很大之差異，可藉由一系列之測試可間接證明聚電解質吸附採逐步吸附。利用穿透式電子顯微鏡觀測可估算出單層聚電解質層約30-45 nm左右，而全反射紅外光光譜可得知改質後有聚電解質之官能基存在，原子力顯微鏡觀測到當吸附上4層聚電解層時膜材表面開始有非均相(non-homogeneous)層產生；X光光電子能譜分析能證明磺酸根可穿透過聚電解質層達到外層。 在滲透蒸發實驗中，當Nafion膜表面吸附6層聚電解質層時，使用進料為9.6 wt %甲醇水溶液，滲透端甲醇水溶液濃度僅0.33 wt %對於甲醇之阻隔性非常好，可避免在甲醇燃料電池上，甲醇溢流 (crossover)之現象發生；在質子傳導率方面，操作溫度80℃、相對溼度95 %下，吸附6層聚電解質層之導電度為2.4×10-1 S/cm，大於Nafion-117導電度3.2×10-2 S/cm，由以上幾種結果可以判斷，吸附6層聚電解質層之Nafion膜材有應用於直接甲醇燃料電池之價值。
並列摘要
In this study, Nafion-117 membranes were modified by layer-by-layer electrostatic self assembly (LBLESA) technique and tested for their application as proton exchange membranes in direct methanol fuel cells (DMFCs). Polyelectrolyte multilayered (PEM) membranes were constructed by electrostatic absorbed polycation poly(allylamine hydrochloride) (PAH) and polyanion poly(acrylic acid) (PAA). A series of standard methods were used to characterize the membrane properties, such as ATR-FTIR analysis, contact angle experiment, XPS analysis, TEM observation, AFM observation, water uptake test, pervaporation test of aqueous methanol solution, AC impedance analysis. The properties of modified membranes were compared with those of pristine Nafion-117 with an aim to be used for the fabrication of membrane electrode assembly (MEA). Polycation and polyanion layer showed difference in water contact angle；therefore monolayer adsorption of polyelectrolytes could be confirmed. The averaged thickness of each layer in the multilayer was about 30-45 nm by TEM observation. ATR-FTIR confirmed the presence of polyelectrolyte element group in the modified membranes. After absorbed four double layer, membranes surface have a non-homogeneous layer growth by AFM observation. XPS analysis suggests the sulfonate group through polyelectrolyte layer as a path to permit easy proton transport. In pervaporation experiment, Six double layers were sufficient to minimize the methanol crossover ( 9.6 wt % in feed, methanol conc. of permeate 0.33 wt% ). The proton conductivity of LBL6 (σ = 2.4×10-1 S/cm) was higher than Nafion-117 membrane (σ = 3.2×10-2 S/cm) at 80℃, relatively humidity of 95 %. Base on all tested results, LBL6 membranes have potential to be used for DMFC.
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