Nafion®/SBA-15質子交換複合膜之製備及其於直接甲醇燃料電池電解質之應用

Abstract

直接甲醇燃料電池因甲醇擁有高能量密度、不易揮發的特點而可作為可攜帶式電子產品的能量來源，此種電池的操作溫度低，也可以保持其中電解質質子交換膜的含水度。甲醇燃料電池的電解質為質子交換膜，需要將質子從陽極傳到陰極，也必須具備防止甲醇穿透的能力，才不會使電池陰極被毒化造成電壓降低以及電池壽命減短。商業化的質子交換膜Nafion® 具有高穩定性及不錯的質子傳導能力，但是其甲醇穿透度也高。為了克服甲醇穿透的問題，同時保有良好的質子傳導效果，本研究以介孔SBA-15作為Nafion質子交換膜的填充材料，使用溶劑揮發法添加介孔SBA-15材料進入Nafion®，製成複合膜。SBA-15材料的模板試劑可以當作質子的固態溶劑，也可以幫助質子傳導，因此在本研究中討論加入不同形貌的SBA-15材料、有無保留SBA-15的模板試劑、將SBA-15接上幫助質子傳導的磺酸根官能基、以及使用不同的溶劑來進行溶劑揮發對複合膜表現的影響。填充材料的性質以小角度X光繞射儀、氮氣吸脫附及掃描式電子顯微鏡來鑑定，複合膜的性質則以螺旋測微器量測其厚度、測量甲醇穿透度、質子傳導率、計算選擇率以及測量全電池表現來鑑定。

Direct methanol fuel cell (DMFC) is considered a promising power supplier for various applications because of its high theoretical energy density of methanol, low emission, and moderate operation temperature. Generally, a high selective membrane with high proton conductivity and low methanol crossover is suitable for DMFC. Commercialized Nafion® exhibits high chemical stability and proton conductivity, but suffers high methanol crossover which leads to decrease of cell voltage and lifetime. In the present study, mesoporous SBA-15 silica was used as the additive of Nafion membrane. Mesoporous silica SBA-15 of different morphologies with and without surfactant are synthesized then imbedded into the Nafion® membrane by solvent-recasting procedure using N,N’-dimethylacetamide (DMAc) and 2-propanol (iPA) as the solvents. Pore directing agent of SBA-15, P123, can serve as nonaqueous proton transporter which may assist proton conductivity of composite membrane. The additive materials were characterized with powder-XRD, N2 sorption, and SEM. The characteristics of composite membranes prepared by solvent recasting procedure were examined with thickness from spiral micrometer, methanol permeability, proton conductivity, selectivity, and single cell performance test.