燃料電池質子交換膜用磺酸化聚醚醚酮之製備與性質研究

Preparation and Properties of Sulfonated Poly(ether ether ketone) for Proton Conducting Membrane in Fuel Cell

吳漢朗(Han-Lang Wu)

指導教授 ： 馬振基

國立清華大學/工學院/化學工程學系/博士(2006年)

https://doi.org/10.6843/NTHU.2006.00671

摘要

本論文旨在研究磺酸化聚醚醚酮之製備方法，及其利用於燃料電池質子交換膜之可行性與相關性質。藉由後磺酸化步驟改質聚醚醚酮，隨著磺酸化程度增加，同時增加質子導電度。本研究發現，質子導電度的提昇會增加膜材對水或其他溶劑之膨潤程度，但降低膜材之尺寸安定性。為了要維持高質子導電度，同時降低膜材之含水率，本研究將磺酸化聚醚醚酮混摻不同的高分子來達成此目的。
本論文主要分為四部分，第一部份討論磺酸化聚醚醚酮之溶解度參數。研究結果發現，磺酸化聚醚醚酮的溶解度參數為26.4 J1/2 · cm-3/2與35.7 J1/2 · cm-3/2，與Nafion®同樣具有兩個溶解度參數(19.8 J1/2 · cm-3/2與35.3 J1/2 · cm-3/2)。由理論計算之磺酸化聚醚醚酮之溶解度參數為26.1 J1/2 · cm-3/2，這個數值與其中之一的實驗值相同。由理論之溶解度參數，經由Flory方程式可計算出理論之磺酸化聚醚醚酮在不同溶劑下之體積分率。當溶劑之溶解度參數小於35 J1/2 · cm-3/2，由van Krevelen方法推算之磺酸化聚醚醚酮，在不同溶劑下之體積分率與實驗值差異不大，但是當溶解度參數大於35 J1/2 · cm-3/2時則有明顯之差異，本論文認為這是來自於磺酸化基團存在的關係所造成。磺酸鈉鹽型態之磺酸化聚醚醚酮，相較原本之磺酸化聚醚醚酮，具有較低之溶劑膨潤程度。
本論文第二個部分探討磺酸化聚醚醚酮與聚醚碸聚摻合物，應用於質子交換膜之含水率、甲醇滲透率與質子導電度等性質。經過交錯極化魔角旋轉(magic angle spinning)之固態核磁共振儀分析，發現磺酸化聚醚醚酮之分子運動性會隨著聚醚碸添加量增加而降低。比較不同聚醚碸含量之聚摻合物玻璃轉移溫度，發現較不符合Fox方程式所預測的結果，而是相對地較符合Kwei方程式預測的結果，因此可知磺酸化聚醚醚酮與聚醚碸之間，可能存在特殊作用力(specific interaction)。本研究推測由於這特殊作用力，使得聚摻質子交換膜具有更低的甲醇滲透率與含水率。
本論文第三部分探討分別用聚乙烯砒咯烷酮(poly(vinylpyrrolidone) (PVP))、聚芳香族羥基醚氰苯(poly(arylene ether benzonitrile) (BPCN))、聚醯胺醯亞胺(poly (amide imide) (PAI)) 摻混磺酸化聚醚醚酮，探討磺酸化聚醚醚酮摻混不同含氮高分子，其膨潤程度之影響。第三部分又分為三小部分，第一小部分探討磺酸化聚醚醚酮與聚乙烯砒咯烷酮聚摻合物之質子傳導膜相關特性。研究發現，由於聚乙烯砒咯烷酮之高親水性，其形成之聚摻膜材之含水率，並不會隨著其含量增加而下降。然而，因為聚乙烯砒咯烷酮與磺酸化聚醚醚酮之間存在強特殊作用力，造成極低的甲醇滲透率。此外，因為高含水率，所以質子導電度並沒有明顯降低。當聚乙烯砒咯烷酮之含量為20 wt%時，具有最大的特殊作用力，使得聚摻膜材具有最低的甲醇膨潤率與甲醇滲透率。本研究同時利用這個比例的聚摻膜材進行膜電極組之組裝測試，並與商用材Nafion® 117做比較。相較於Nafion® 117，聚摻合膜材的開路電壓為0.72V，較Nafion® 117高(0.63V)，且極化情形也較低，SPEEK在電壓為0.15V時，電流密度大於80 mA cm-2，而Nafion® 117在0.15V電壓下電流密度只有63 mA cm-2。
本論文第三部分中的第二小部分探討磺酸化聚醚醚酮混摻聚芳香族羥基醚氰苯。聚芳香族羥基醚氰苯是藉由2,6-雙氯苯腈(2,6-dichlorobenzonitrile)與雙酚(biphenol)聚合而成。本研究改變不同聚芳香族羥基之分子量，其分別為1,641,060及185,976 g mole-1。在相同的摻混重量百分比下，高分子量之聚芳香族羥基醚氰苯，對磺酸化聚醚醚酮膨潤程度之降低，較低分子量樣品明顯。透過霍式轉換紅外光譜研究，聚芳香族羥基醚氰苯與磺酸化聚醚醚酮之分子間作用力(inter molecular force)。結果顯示，聚芳香族羥基醚氰苯之氰基波峰有位移的現象。另外，酮基訊號之側波峰隨著聚芳香族羥基醚氰苯含量增加而有增大的趨勢，顯示磺酸化聚醚醚酮與聚芳香族羥基醚氰苯間存在較弱的分子作用力。另外，本研究同時討論磺酸化聚醚醚酮與聚芳香族羥基醚氰苯聚摻合物之熱性質，包含玻璃轉移溫度與熱重損失溫度，摻混30 wt. %聚芳香族羥基醚氰苯之磺酸化聚醚醚酮之玻璃轉移溫度，由196 oC下降至175 oC。
本論文第三部分之第三小部分探討磺酸化聚醚醚酮與聚醯胺醯亞胺聚摻合物之質子傳導膜相關性質。藉由固態核磁共振儀與霍式轉換紅外光譜鑑定其化學結構。探討聚摻膜材之溶解度參數對水或甲醇之膨潤程度之影響。此外，比較不同含量聚醯胺醯亞胺之聚摻膜材其水擴散係數與質子導電度之關聯性。相較於Nafion®，本研究所製備之聚摻膜材具有較低的甲醇滲透率與質子導電度。從質子甲醇選擇率(即質子導電度除於甲醇滲透率之比值)來看，本研究所製備之聚摻膜材之選擇率為3.46 x 104 S s cm-3，與Nafion® 3.30 x 104 S s cm-3相近。
本論文第四部分以SPEEK摻混二氧化矽之方式，藉由表面改質胺鹽二氧化矽與SPEEK間形成酸鹼作用力，藉此來降低膜材在甲醇溶液中的膨潤程度(swelling)。添加30 phr表面改質胺基二氧化矽之樣品，質子傳導度為0.026 S cm-1，而甲醇滲透率為4.71 cm2 s-1。

關鍵字

質子交換膜 ； 燃料電池 ； 磺酸化聚醚醚酮

並列摘要

The objectives of this dissertation are the preparation and characterizations of proton exchange membrane in fuel cell utilizing sulfonated poly(ether ether ketone) (SPEEK) and its blend membranes. A post- sulfonation method was used to enhance the proton conductivity of SPEEK. Both water uptake and solvent uptake were increasing with the increasing of the degree of sulfonation. In order to reduce the swelling of the membrane at high proton conductivity, various polymers were blended with SPEEK.
There are four parts in this dissertation. The first part discusses the solubility parameter of SPEEK. SPEEK exhibited two solubility parameters, 26.4 and 35.7 J1/2 · cm-3/2, which was similar to that of Nafion®. Since Nafion® has two cohesive energy densities. The theoretical solubility parameter of SPEEK, 26.1 J1/2 · cm-3/2, has been determined using the van Krevelen’s method and was correlated to the experimental value. The theoretical volume fraction of SPEEK in the solvent was determined using the Flory’s equation. The trend of theoretical volume fraction of SPEEK was fit quite well with the experimental results when the solubility parameter of solvent was lower than 35 J1/2 · cm-3/2. The significant deviation of the experimental volume fraction of SPEEK in high solubility parameter was resulted from the presence of sulfonic acid group. SPEEK with sulfonated group in sodium form (SO3Na) exhibited the reduced solvent absorption in comparison with the one in acid form (SO3H).
The second part of this dissertation describes the preparation of polymer blends of SPEEK and poly (ether sulfone) (PES). The investigation on water uptake, methanol uptake, permeability and proton conductivity has been conducted. The spin-lattice relaxation time (T1ρH) in the rotating frame of PES/SPEEK phase was obtained from the results of cross-polarization magic angle spinning (CP/MAS) solid state 13C NMR. SPEEK blended with PES result in increasing T1ρH, indicating the molecular motion of polymer chain was reduced. The glass transition temperature of the PES/SPEEK blend membranes were predicted by the Kwei equation. PES plays an important role in reducing water uptake, methanol uptake and methanol permeability while enhancing the thermal stability of the blend membrane, which shows the feasibility for direct methanol fuel cell.
The third part of this dissertation was the investigation on the blend of SPEEK with nitrogen-containing polymers. The nitrogen-containing polymers used in this research were poly(vinylpyrrolidone) (PVP), poly(arylene ether benzonitrile) (BPCN), and Poly (amide imide) (PAI). The first sub-part is the SPEEK/PVP acid-base polymer blends, which was designed to reduce methanol uptake and to decrease methanol permeability while maintaining high proton conductivity. The acid-base interaction occurring on the sulfonic acid group and on the tertiary amide group was characterized by FT-IR and DMA. As the composition of PVP is lower than 20 wt. % in the blends, the acid-base interaction causes great reduction on methanol uptake and the methanol permeability, however, the proton conductivity is still high. In this work, membrane-electrode assemblies (MEAs) have been prepared for direct methanol fuel cell (DMFC) from both blend membrane and Nafion® 117. DMFC single cell performance was also evaluated. Results confirmed that SPEEK with the degree of sulfonation (DS) = 69% blended with PVP (Mn=1,300,000) at a ratio of 80/20 (w/w) exhibits higher open-circuit voltages (OCV), 0.73 V and lower polarization loss (0.15V, current density > 80 mA cm-2) than those of Nafion® 117 (0.15V, current density > 60 mA cm-2). The acid-base blend membrane will be suitable for DMFC application.
The second sub-part was the SPEEK blended with poly(arylene ether benzonitrile), BPCN, which was synthesized using 2,6-dichlorobenzonitrile and biphenol. Two molecular weights of BPCN 1,641,060 and 185,976 g mole-1 were synthesized by controlling the stoichiometry of the monomers and were blended with SPEEK. The higher the molecular weight of the BPCN in the blends, the lower the degree of swelling can be obtained. At the same ion exchange capacity, the SPEEK blended with high molecular weight of BPCN resulted in the lower water uptake, low swelling, low lambda value, and low methanol permeability comparing to the one with low molecular weight. The molecular interaction between SPEEK and BPCN was studied by FT-IR. From the increasing shoulder peak of carbonyl of SPEEK and the slightly shifted peak of nitrile of BPCN, it was suggested that the molecular interaction between these two functional groups were existed. The glass transition temperature and thermal stability of SPEEK/BPCN blends was also discussed in this study.
The third sub-part was the SPEEK blended with poly(amide imide), PAI, which was synthesized using 1,2,4-benzenetricarboxylic anhydride (BTBA) and 4,4’-methylenebis (phenyl isocyanate) (MBPI). SPEEK/PAI blend membranes were prepared and the properties were investigated by NMR, GPC, FT-IR and AFM. The chemical structures of PAI and SPEEK were characterized by using NMR and FT-IR. The adsorption of the SPEEK/PAI blend membrane of water or methanol solution was also characterized. The significant swelling of the blend membrane in concentrated methanol solution was explained by the solubility parameter. The water diffusion coefficient (DH2O) was related to the lambda value of the membrane. The SPEEK/PAI blend membrane had a lower proton conductivity and methanol permeability than that of Nafion® 117. Furthermore, the relative selectivity (proton conductivity divided by methanol permeability) of the SPEEK/PAI 70/30 w/w blend membrane was 3.46 x 104 S s cm-3, which is closed to that of Nafion® 117 (3.30 x 104 S s cm-3).
The fourth part describes the amine salt modified colloidal silica blended with SPEEK. By means of the acid-base interaction between the modified silica and SPEEK, the swelling and methanol uptake of the membranes were reduced. Although the proton conductivity was decreased up 50 %, the 80 % reduction was found in the methanol permeability. The composite membrane with 30 % amine salt modified silica is suitable for further DMFC application.

並列關鍵字

Proton Conducting Membrane ； Fuel Cell ； Sulfonated Poly(ether ether ketone)

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