| Fuel cell is an electrochemical apparatus that the chemical energy of fuel with out fuel combustion turned to electrical energy, which is considered to be a promising technology for efficient, clean and environmental power generation in the twenty-first century. Direct methanol fuel cell (DMFC) has attracted attention as an ideal resource and offers a reasonably high fuel energy density, a readily stored and available liquid fuel, ease of refueling, and direct and complete electrooxidation of methanol. Proton exchange membranes (PEMs) are the key component in fuel cell system. Well-studied perflurosulfonic acid proton exchange membranes such as Nafion have been the referenced ones due to their high chemical stability as well as excellent electrochemical properties; however, they have a limitation for large-scale commercialization under anhydrous or low-humidity conditions because of their high cost and methanol cross over. Consequently, PEMs with high proton conductivity, environmental-affability with low methanol crossover, and production cost have attracted considerable application-driven interest recently for problem solving in current technology.Sulfonate poly (aryl ether sulfone)s (SPES) have been investigated extensively as a promising candidate for their excellent chemical and thermal stability,good mechanical property as well as conductivity. Nano-sized organic-inorganic hybrid materials are attracting increasing attention for they constitute a unique class of materials which can combine the advantages of organic moieties (eg., flexibility, dielectric, ductility, and processabiliy) and the inorganic materials(eg., rigidity, and thermal stability) together. Nanosilicas exhibit good water retention ability and efficiently hinder methanol to crossover by changing the length and size of transportation channel, and they play a reinforce role between the filler and polymer matrix. Nanocomposite membranes are prepared by a solution casting method, and sulfonic acid functionalized silica dispersed in the membrane matrix. It is expected that functionalized silica in polymer chain will balance its hydrophilic-hydrophobic nature, reduce methanol permeability, and enhance proton conductivity as well as thermal and mechanical stabilityOrganic-inorganic hybrid cross-linked membranes SPES/TEOS/TPABS for direct methanol fuel cells (DMFC) were synthesized by incorporation a zwitterionic silica precursor containing sulfonic acid and ammonium groups,3-[[3-(triethoxysilyl)-propyl]amino]butane-l-sulfonic acid (TPABS), with tetraethoxysilane (TEOS) and sulfonated poly(ether sulfone)(SPES) using the sol-gel process with the goal to obtain high proton conductivity and low methanol permeability as well as good stability. The structural variation impacting on their properties such as thermal stability, oxidative stability, solvent uptake, proton conductivity, methanol permeability and water retention ability have been investigated systemically. All of the membranes are thermal and oxidative stable. With the increasing content of inorganic zwitterionic TPABS, the morphology of the membranes became more uniform and formed denser and-SO3-richer cross-linked networks, consequently lead to higher proton conductivity and lower methanol permeability. It notes that the proton conductivity reached as high as Nafion117, whereas the methanol permeability has been greatly reduced by forming the cross-linked structures. Among these membranes, SPES/TEOS/TPABS-70(70wt%to SPES of TPABS in the membrane matrix), showed the best performance with proton conductivity of7.24×10-2Scm-1, methanol permeability of2.46×10-7cm2s-1, ion-exchange capacity value of1.37mequiv./g and comparable selectivity parameter of2.63×105S cm-3s. The new designed cross-linked membranes could thus be a promising candidate to satisfy the requirements of proton exchange membranes for DMFC application. |
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