有機無機複合質子傳導膜中混摻的無機粒子通常有分散性不佳和低質子傳導度的缺點,因此如何製備分散性佳且擁有良好質子傳導度的無機奈米粒子對質子傳導膜來說是個重要課題。本實驗共採用兩種方式希望達到上述的目標,第一部分是利用合成本身具有良好質子傳導度的α-zirconium phosphate sulfophenylenphonates (α-ZrSPP)直接混摻成質子傳導膜;第二部分則合成溶解度佳且本身也具有質子傳導度的聚磺酸苯乙烯(ZrC-PSStNa)作為添加物,再進行混摻形成質子傳導膜。 在第一部分,我們將剛合成好的α-ZrSPP混合物直接和Nafion®溶液混摻為複合膜。我們系統化研究了複合膜中關於α-ZrSPP混摻量和α-ZrSPP顆粒大小對複合膜的質子傳導性質影響,並從SEM斷面圖中發現混摻有顆粒小且SPPA含量低的α-ZrSPP粒子之複合膜可以達到較均勻的分散性。複合膜的吸水率和離子交換容量(IEC)隨著α-ZrSPP添加量的增加而上升。且SPPA含量少者離子交換容量較高。而複合膜的質子傳導度則因所添加α-ZrSPP的特性和其在內部分散情況不同,進而有複雜的行為。一般而言,隨著α-ZrSPP混摻量增加,其質子傳導度顯示出先升後降的趨勢,代表在過量的α-ZrSPP混摻量之下,複合膜的質子傳導途徑可能被破壞。混摻有顆粒大且SPPA含量低的α-ZrSPP之複合膜有最高的質子傳導度。此外,混摻有顆粒小但SPPA含量高的α-ZrSPP之複合膜能抑制甲醇滲透因而有良好的選擇性,甚至可以達到Nafion® recast的5倍。在α-ZrSPP的保水能力幫助下,複合膜在高溫低濕下也有不錯的質子傳導度。 第二部分中,我們使用兩種不同溶劑來進行聚合ZrP-PSStNa 反應(使用甲醇者為M粒子,使用NMP者為N粒子),這些粒子因使用溶劑不同而造成不同的顆粒大小和微結構。我們將合成之ZrP-PSStNa和Nafion®混摻為複合膜,並系統化研究PSStNa分子量大小、顆粒大小和形態對複合膜中ZrP-PSStNa分散性和質子傳導途徑的影響。複合膜的吸水率和離子交換容量(IEC)隨著ZrC-PSStNa添加量的增加而上升,且ZrC-PSStNa分子量高者離子交換容量較多。而複合膜的質子傳導度則因所添加ZrC-PSStNa不同和其在內部分散情況不同,而有複雜的行為。一般而言,M膜質子傳導度顯示出先升後降的趨勢,而N膜則是隨混摻量增加而增高。SEM斷面圖顯示含有較高分子量的PSStNa之N粒子複合膜表現有較佳的分散性。此外,在N膜且分子量較大的複合粒子少量混摻下,對甲醇滲透有不錯的阻擋,因此其複合膜會表現出較高的選擇性。在高溫或低濕下只要有混摻ZrC-PSStNa粒子之複合膜均能維持其質子傳導度,甚至能達到Nafion®的2.5倍。
Most of the inorganic additives used in organic/inorganic composite proton exchange membranes (PEMs) generally exhibited low intrinsic proton conductivity and difficulty in forming homogeneous dispersion of nanoparticles within the membrane. Therefore, the development of inorganic nanoparticles having good proton conductivity and capability of homogeneous dispersion is critical for the further improvement of the composite PEMs. In this study, two different strategies are employed to achieve the above mentioned targets. The first approach is to develop a new methodology of the preparation of the composite membranes using highly proton conductiveα-zirconium phosphate sulfophenylenphonates (α-ZrSPP). The second approach is to synthesize zirconium phosphate-poly(styrene sodium sulfonate) (ZrP-PSStNa) composite nanoparticles with high proton conductivity and good solubility as the additives for the composite membranes.. In the first part, the membranes are prepared by solvent casting from the blends of the reaction mixture of as-synthesized α-ZrSPP and Nafion® solution. The effect of composition, particle size and loading amount of α-ZrSPP on the distributions of α-ZrSPP within the membranes and the transport properties are systematically investigated. SEM cross-sectional images suggest that smaller particles with lower zirconium sulfophenylphosphonate (SPPA) content are more feasible to form homogeneous blends within the composite membrane. With increasing loading ofα-ZrSPP, water uptakes and ion exchange capacities of the composite membranes increase.α-ZrSPP having lower SPPA contents generally lead to higher IEC. Proton conductivity exhibits complicated trends as affected by both the properties and the distribution ofα-ZrSPP as well as the morphologies of the composite membrane. Generally, proton conductivity increased first and then decreased with increasing loading ofα-ZrSPP, indicating the existence of an optimal loading and overloading of ZrSPP would damage the proton conduction pathways. Large ZrSPP particles with lower SPPA contents lead to the highest proton conductivity of the composite membrane. In addition, the incorporation of small α-ZrSPP with high SPPA contents resulted in significantly suppressed methanol permeability and dramatic improved selectivity, at most a 5 fold increase comparing with the pristine Nafion recast . The composite membranes also show improved proton conductivity at low relative humility and elevated temperature, probably owing to the water retention and the proton conduction originated from ZrSPP. In the second part, two series of ZrP-PSStNa composite particles with different lengths of PSStNa are synthesized by changing the solvent (methanol for M-particles or NMP for N-particles) for polymerization, and the morphologies and the sizes of these particles are significantly affected by the solvent used. The membranes are prepared by solvent casting from the blends of the solution of ZrP-PSStNa and the Nafion solution. The effect of the molecular weight of PSStNa, the particle size/morphology and the loading amount of ZrP-PSStNa on the dispersions of the composite particles within the membranes and the transport properties are also systematically investigated. With increase loading of ZrC-PSStNa, water uptakes and IEC of the composite membranes increase and ZrC-PSStNa having large molecule weight of PSStNa generally lead to higher IEC. Proton conductivity behaves complicatedly, affected by the intrinsic properties and the dispersion of ZrC-PSStNa as well as the morphologies of the composite membrane. Generally, with increasing loading of ZrC-PSStNa, proton conductivity of the composite membranes containing M-particles increased then decreased, but the membranes containing N-particles increased consistently. The SEM cross-sectional images show that N-particles with PSStNa of larger molecule weight can be blended more homogeneously within the composite membranes. The composite membranes containing low loading of N-particles with large molecule weight PSStNa show better selectivity owing to suppressed methanol crossover. Furthermore, the proton conductivity of the composite membranes at low relative humility and high temperature was enhanced significantly, up to a 2.5 fold increase comparing with the pristine Nafion recast.