含有磷酸鋯衍生物之質子傳導複合膜:磷酸鋯衍生物之合成與複合膜製備及特性研究

Abstract

本實驗利用控制溫度、溶劑和進料比例等實驗參數，以不同的反應條件來控制α-zirconium phosphate sulfophenylenphosphonates (α-ZrSPP)之組成成分、晶粒大小和顆粒大小。當溶劑由水改為弱鹼性之N-甲基-2-四氫吡各酮 (NMP)時，雖然觀察到所合成的α-ZrSPP晶粒大小有些微的增加，但顆粒大小卻大幅的下降。在同樣的反應溫度及進料比例的反應條件下，以NMP為溶劑所得的α-ZrSPP會有較高含量的SPPA。由低溫(室溫)製程所得的α-ZrSPP，其晶粒大小與顆粒大小皆隨著反應進料的m-sulfophenylphosphonic (SPPA)添加量的增加而上升；然而高溫製程(>80°C)所得的α-ZrSPP，其晶粒大小隨SPPA的添加量增加而縮小，但顆粒大小則呈現先下降後上升的趨勢。一般來說，較低的反應溫度所得的α-ZrSPP會有較高的SPPA含量。 將不同成分、不同顆粒大小之α-ZrSPP和Nafion&reg;的NMP溶液以不同比例進行摻混並將溶劑揮發製成複合質子傳導膜。複合膜之吸水率會隨著α-ZrSPP添加量的增加而隨之上升；通常所添加之α-ZrSPP之SPPA含量越高，則複合膜的吸水率越高。複合膜的離子交換容量(IEC)跟質子傳導度(proton conductivity)受到所添加的α-ZrSPP的特性，其在膜內分散的情形及膜的微結構所影響而顯現出複雜的行為。當所添加的α-ZrSPP的粒徑>40nm且SPPA的含量較低時，複合膜的IEC值隨著α-ZrSPP添加量的增加而上升；但其質子傳導度卻呈現相反的趨勢。當所添加的α-ZrSPP的粒徑<40nm且SPPA的含量較低時，複合膜的IEC值與質子傳導度與α-ZrSPP添加量的關係呈現複雜的走勢。當α-ZrSPP的SPPA含量較高時，所對應的複合膜的IEC值並不會隨著α-ZrSPP添加量的上升而有所變化，但質子傳導度則呈現先上升後下降的趨勢。有趣的是，含有顆粒最小且SPPA含量最高的α-ZrSPP的複合膜並沒有得到最高的IEC及質子傳導度。然而顆粒越小的α-ZrSPP越能有效阻擋甲醇的穿透，且只需要少量的α-ZrSPP的添加(<10wt%)。通常顆粒越小且SPPA含量越高的α-ZrSPP會有較好的分散性，因此其複合膜會表現出較好的選擇性。添加了5wt% α-Zr(HPO4)0.36(SPPA)1.64之Nafion 1100&reg;複合膜將選擇率由重製的Nafion&reg;膜的4600提升至22000。

In this study, α-zirconium phosphate sulfophenylenphosphonates (α-ZrSPP) were prepared via various reaction conditions to control their compositions, crystal domain sizes and particle sizes. The properties of α-ZrSPP were affected by the reaction temperature, the solvent and the ratio between different reactants in the feed. When NMP, a basic organic solvent, was used as the solvent instead of water, the crystalline sizes of the obtained α-ZrSPP were slightly larger than those of α-ZrSPP synthesized from water while the particle sizes were significantly smaller. α-ZrSPP obtained from NMP had higher SPPA (m-sulfophenylphosphonic acid) contents than those from water did when both of them were synthesized at the same temperature with the same SPPA/H3PO4 ratio in the feed. When the reaction temperature was low (for example, room temperature), high SPPA/H3PO4 ratios in the feed would lead to large particle sizes and large crystalline sizes. However, when the reaction was carried out at high temperatures (>80°C), the resulted α-ZrSPP exhibited decreasing crystalline size with incresing SPPA/H3PO4 ratio in the feed; in addition, the minimum particle sizes were observed from the reactions with SPPA/H3PO4=3. Higher SPPA contents ofα-ZrSPP were obtained from the low temperature reactions. Different amount of α-ZrSPP with various sizes and compositions was blended with Nafion&reg; solution in NMP and the composite membranes were obtained from these mixtures by solvent casting. With increasing loading of α-ZrSPP, water uptakes of the composite membranes increased andα-ZrSPP having high SPPA contents generally led to higher water uptakes. Ion exchange capacity (IEC) and proton conductivity were complicated functions of the properties and the distribution of α-ZrSPP as well as the morphologies of the composite membranes. When the particle sizes of α-ZrSPP were larger than 40nm and the SPPA contents were low, the IEC values of the composites increased with increasing loading while the proton conductivities decreased. When the particle sizes were below 40nm, IEC and proton conductivities of the composites showed a mixed trend. When the SPPA contents of α-ZrSPP were high, the IEC value retained as a constant regardless the loading while the proton conductivities show a convex trand with increasing α-ZrSPP loading. Interestingly, α-ZrSPP particles having high SPPA content and small particle sizes were not necessarily providing their corresponding composite membranes the highest proton conductivity. Nevertheless, when smaller α-ZrSPP particles were used as fillers, the methanol crossover could be substantially suppressed with a small amount of α-ZrSPP loading. In general, composite membranes containing small α-ZrSPP particles with high SPPA contents showed better selectivity (conductivity/methanol permeability) owing to more homogeneous distribution of α-ZrSPP in the membrane. The 5wt% α-Zr(HPO4)0.36(SPPA)1.64/Nafion 1100&reg; composite membrane showed a selectivity of approximately 22000, which was much improved than that (4600) of the recast Nafion&reg; membrane.