Synthesis Of Novel Proton Exchange Membrane And Effect Of The Electron Beam Radiation On Its Properties

Energy sources are the foundation of economics. There are many revolutions ofthe way to utilize energy in history, from original steam engines to gas turbine andinternal-combustion engine, each time the revolution accelerated modern civilizationgreatly. However, two main disadvantages still exist: first, limited by the Kano cycle,the conversion from chemical energy to heat and then to mechanical energy orelectricity wastes most of the energy, the final conversion efficiency is only 33-35%;second, the conversion process causes serious environmental pollution. Forconquering these drawbacks, fuel cell technique comes into being.Fuel cells can convert chemical energy to electricity directly by electrodereaction. The electrode reactant is not stored inside of the cell but provided from theoutside equipments. The conversion efficiency of energy is high and there is nopollution during the power generation process, so fuel cell technique is the mostpromising clean power in the future.Proton exchange membrane (PEM) is the heart of a proton exchange membranefuel cell (PEMFC), which plays an important role in separating fuels and oxidantand conducting protons. Most PEMs are constituted by polymer matrix and sulfonicacid groups. These acid groups transport protons by H2O. Currently commercialused PEM is Nafion (Dupont) but the high cost limits the large-scale applications offuel cells. So developing new kinds of PEMs with superior performance and lowercost is attracting more and more attention nowadays, especially the non-fluonatedpolymer materials.Poly (aryl ether ketone) (PAEK) is a semi-crystalline thermoplastic materialwith excellent thermal stability, electrochemical performance and good chemicalresistance. PAEKs have already played an important role in electronic appliances,transportation, aerospace technology etc.According to the excellent properties of PAEKs, we synthesized two kinds ofPAEKs as precursors of sulfonated proton exchange membranes. Through the newmonomer tri-oligomer containing thio-ether band, we successfully introduced thethio-ether structure into the polymer main chain. One kind of the PAEK containsonly the thio-ether structure (PETEK) and another kind contains both the thio-etherstructure and the trifuoromethyphenyl(PETEK-CF3). We characterized two kinds ofpolymer by FTIR,DSC,TGA,WAXD etc.. Both of the two kinds of polymermaintain the good performance of PAEKs, but PETEK-CF3 is no longer crystallinebut amorphous because of the bulk-substituent, which also improved the solubilityof the polymer.We used concentrated sulfonic acid (98%) to introduce sulfonic acid group intothe two kinds of polymer chain through post-sulfonation procedure. The degree ofsulfonation rises with the sulfonation time. Solubility of the polymer is improved alot by the sulfonic acid group but the 5% decomposed temperature declined.However, TGA analysis shows the sulfonated polymers are stable under 200℃,which means these materials can be used in fuel cells totally.The sulfonated polymers were dissolved in DMAc and cast onto a glass plate toobtain a series membranes. Then these membranes were radiated under a linearelectronic accelerator in the air atmosphere, the radiation dose is 200kGy and400kGy separately. The color of these membranes turns deep after radiation. Wecharacterized the sulfonated polymers before and after radiation by WAXD,DSC,TGA,Solartron SI126 Impedance/Gas-phase Analyzer and SI1287 Electro chemicalInterface analyzer.The testing results indicated that electron beam radiation brought someinfluence on the properties of the membranes at a certain extent. Ion exchangecapacity, water uptake and swelling ratio all decreased after radiation. Protonexchange ability is related with the radiation dose, degree of sulfonation and testingtemperature. Radiation damaged the sulfonic acid group of the membrane and maychange the microstructure of the membrane at the same time. With appropriateradiation dose and sulfonation degree, the proton exchange ability of the membranesis good enough for the fuel cell application. Performances of the polymer withtrifuoromethyphenyl were inferior to the polymer without the bulk substituent.The next research point is the study of the influence on the microstructurebrought by radiation.