Preparation,Characterization Of Proton Exchange Membranes Via Polyacylation For Fuel Cells

Because of the excessive consumption of fossil energy and the increasingly serious environmental issues. Proton exchange membrane fuel cells (PEMFC) have attracted great attention due to their high energy efficiency and low polluting emissions. Proton exchange membrane(PEM) is a key component playing a critical role in PEMFC's performance such as proton transport media and fuel barrier. To date,the most commercially used PEM is perfluorosulfonic acid copolymer membranes,Such as Nafion. This kind of membrane have so many advantages as well as some drawbacks,such as the expensive cost. In addition,high methanol crossover of perfluorosulfonic acid copolymer became a serious problem in the Direct methanol fuel cells (DMFC) application. Therefore, it's very urgent to find some alternative materials with good performance and low cost. Sulfonated polyimides has been identified as one of the most promising material for PEMFC application due to its good film formation ability and thermal stability. In addition, the Sulfonated polyimides have good resistance towards methanol which make it become the most promising candidate for DMFC applications.Decomposition of polyimides usually happened during post-sulfonation procedure, therefore, the most commonly used synthetic route to produce sulfonated polyimides is the "Direct copolymerization of sulfonated monomers". People usually synthesis sulfonated polyimides through polycondensation of sulfonated/nonsulfonated diamine and dianhydride monomers. The reaction temperature is very high and need to employ a extremely excitant solvent: m-cresol.In addition, some starting monomer of this kind of reactions like side-chain-type sulfonated diamine is very complicated to synthesis due to the amino-protection procedure.Under the above background, in this thesis, novel side-chain-type sulfonated polyimides were synthesized via a electrophilic substitution reaction: polyacylation of ionic monomers. Meanwhile, some modifications of the polymer structure has be done to improve the properties of the proton exchange membrane, The main contents are as follow:(1) Perylene has a strong ?-? configuration that could improve the intermolecular force. However, the poor solubility limited it's application. In this thesis, novel side-chain-type sulfonated polyperylenebisimides with different sulfonation degree was successfully synthesized via polyacylation of a pre-produced perylenebisimides-containing diarene monomer(PBI-1) and a side-chain-type diarene monomer(SBP) and 4,4-oxydibenzoic acid. Eaton's reagent and trifluoromethanesulfonic acid mixture(PPMA-TFSA)was used as the catalyst and solvent. The whole procedure including the synthesis of SBP was very mild and easy to control, indicating the great potential for this route in the synthesis of sulfonated polyimides. The obtained SPI-x membranes showed high proton conductivity as Nafion due to the flexible side chain. Meanwhile, the low swelling ratio and low methanol permeability were obtained due to the strong ?-? conjugation of the perylene moieties.(2) Novel side-chain-type sulfonated polyimides containing aliphatic long chain were synthesized via polyacylation of SBP with two pre-produced aliphatic-chain-type perylenebisimides diacid monomers, respectively. Because of the strong ?-? conjugation of the perylene and the long chain effect, the molecular self-assembly into a well-ordered stack arrangement. In this arrangement,perylenebisimide units(one side of the aliphatic long chain) stack together because of the conjugation, the sulfonated group units(another side of the aliphatic long chain)aggregate together at the same time due to the hydrophilic interaction. The perylene aggregation improved the resistance of water and methanol, the sulfonated group aggregation improved the proton conductivity. Both membranes AL-SPI-5 and AL-SPI-10 showed high membrane selectivity and better fuel cell performance than nafion115. In addition, the aliphatic long chain connected directly with the imide ring increase the electron density of the imide nitrogen and improve the hydrolytic stability of the membrane.(3) fluorine containing side-chain-type sulfonated polyimides were attempted to be obtained via polyacylation of the sulfonated monomer SBP and 2,2-Bis-(4-carboxyphenyl)hexafluoropropane and diacid monomers. The membrane possess high ion exchange capacity and high proton conductivity. (The proton conductivity of SPIF-5 reached 144.5mS/cm under 30?). However, the relationship between the water stability and the introduction of F need further study.