Study Of Silicane-crosslinked Sulfonated Poly(Arylene Ether Ketone)s Proton Exchange Membranes

Researches on direct methanol fuel cells (DMFCs) are very attractive due to theirunique properties，such as high efficiency，low power-source emissions，as well as thesimplicity of system. Proton exchange membranes (PEM) are the key components ofDMFC systems. Currently，the widely used PEMs are perfluorosulfonic acid membranes，such as DuPont’s Nafion. However，several drawbacks including expensive cost，highmethanol permeability and poor properties at higher temperatures (>80℃) have limitedtheir applicability. Therefore， considerable efforts have been made to search foralternative cost-effective PEMs. Recently，fluorine-free ionomer membranes such assulfonated poly(arylene ether ketone)s (SPAEKs) are attracting a great deal of attention.These materials possess remarkable properties，such as good mechanical properties，excellent thermal stability，and high proton conductivity that can be controlled by thedegree of sulfonation. However，high methanol permeability and water swelling would beinduced due to the increasing number of sulfonic acid groups. Thus，we use severalmethods to modify SPAEK membranes.In this work，we propose a novel efficient method to prepare cross-linked hybridproton exchange membranes by a combination of silane-crosslinking and thiol–ene clickchemistry. Propenyl，containing a double bond，is an excellent cross-linking agent，because it can initiate a radical reaction by heating or UV irradiation. It could be involvedin thermally and photo-chemically initiated thiol–ene click reactions using thiol and allyl functionalized polymers. We chose3-mercaptopropyltrimethoxysilane containing–SHgroups(Trademark: KH590) as a cross-linker for SPAEK membranes containing propenylgroups. We grafted a special silane monomer，KH590，onto the SPAEK backbone by thethiol–ene click reaction.The silane-crosslinking was then induced by ahydrolysis-condensation. The hydrophilic SPAEK could be blocked in the Si-O-Sinetwork，making a contribution to the decrease of swelling and methanol permeability。SPAEK system’s sulfonic acid groups not take part in the reaction of cross-linking。Moreover，other properties of the cross-linked hybrid membranes，such as water uptake，oxidative stability and mechanical properties were also investigated as compared with thepristine SPAEK membrane.Then in Chapter4，we blend SPAEK containing–COOH with two silane monomers:3-glycidoxypropyl–trimethoxysilane(GPTMS)and3-mercaptopropyl trimethoxysilane(MPTMS). GPTMS are grafted to SPAEK when epoxy group cross linked with–COOH.The–SH groups of MPTMS are oxidized to sulfonic acid groups，which are attributed toenhance the proton conductivity of hybrid membranes.The structures of SPAEK and cross-linked membranes are confirmed by Fouriertransform infrared spectroscopy. The Si-O-Si cross-linked structure makes a greatcontribution to the improvement of dimensional and chemical stabilities. The protonconductivity of a cross-linked hybrid membrane G50M50reaches up to0.20S cm-1at80℃，which is comparable to that of SPAEK and much higher than that of Nafion.Meanwhile，the methanol permeability is nearly three times lower than that of Nafion andtwo times lower than that of SPAEK. We also investigated the thermal stability，IEC，water uptake and swelling.