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Synthesis and Properties of Aromatic Polymers for Proton Exchange Membranes

Author: ZhaoLiang
Tutor: HuangYuDong
School: Harbin Institute of Technology
Course: Chemical Engineering and Technology
Keywords: Direct methanol fuel cell Proton exchange membrane Sulfonated poly(phthalazinone ether ether ketone) Sulfonated polyimide Methanol permeability
CLC: TM911.4
Type: PhD thesis
Year: 2008
Downloads: 185
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Abstract


Direct methanol fuel cells （DMFCs） have attracted considerable attention as a portable energy system because of their high efficiency, high energy density, low emissions and environmental friendship. Proton exchange membrane （PEM） is one of the key components of DMFC system. Nafion? membranes are the state-of-the-art PEMs because of their good thermal stability and excellent chemical stability, as well as high proton conductivity. However, high cost and high methanol permeability of Nafion?117 membrane have limited the development and application of DMFC. Therefore, many efforts have been done in the development of PEM materials with low cost and low methanol permeability.Sulfonated poly（phthalazinone ether ketone） （SPPEK） with various degrees of sulfonation （DS） were prepared and characterized by FTIR, NMR and TG analysis. It was found that the water uptake, swelling ratio, proton conductivity and methanol permeability of SPPEK membrane increased with DS level. In comparison with Nafion?117 membrane, SPPEK membrane displayed good methanol-impeding property. SPPEK membrane with a DS level of 0.85 was chosen to prepare composite membrane with phosphotungstic （PWA）. The incorporation of PWA resulted in higher proton conductivity, while sacrificing methanol-impeding property, however, the methanol permeability coefficient （Pm） of SPPEK/PWA composite membrane was still lower than that of Nafion?117 membrane. The DMFC performance of SPPEK/PWA composite membranes was not as good as Nafion?117 membrane and was not improved due to the incorporation of PWA.The diamine monomer, 2-（4-aminophenyl）benzo（1,3）oxazol-5-amine （APBA）, was synthesized by condensation reaction. Various factors controlling the reaction were analyzed by L16 （43） orthogonal experiments. The structure of APBA was determined by FTIR, NMR and element analysis. The HPLC test indicated that the purity of the monomer reached 98.20%. A series of newl naphthalenic sulfonated polyimides （SPI-X） were synthesized using 1,4,5,8-naphthalenetetracarboxylic dianhydride （NTDA）, 2,2’-benzidinedisulfonic acid （BDSA） by one-step high temperature polymerization method. The sulfonated degree of SPI-X membranes was controlled through adjusting the molar ratio of BDSA to the non-sulfonated diamines. The water uptake, swelling ratio, proton conductivity and methanol permeability of SPI-X membranes were also investigated. The proton conductivity of SPI-X membranes decreased with APBA content, but methanol permeability of SPI-X membranes improved compared with Nafion?117.The sulfonated diamines, 4,4’-bis（3-aminophenoxy）biphenyl-3,3’-disulfonic acid （mBAPBDS） was successfully synthesized and characterized. The mBAPBDS was used together with NTDA and common nonsulfonated diamines to prepare a series of sulfonated polyimides （SPIs）. TG analysis indicated that the SPI copolymers displayed good thermally stability with the decomposition temperature of above 300℃.The IEC value of SPI membranes prepared by solution casting method was 1.87-2.49mmol/g. The experimental results confirmed the assumption of complete imidization. Proton conductivity of SPIs membranes increased with DS level. The optimal proton conductivity of 8.65×10-3S/cm at room temperature was comparable to that （9.80×10-3S/cm） of Nafion?117 membrane. It was also found that SPI membranes with IEC of 2.00mmol/g displayed adequate water uptake and good dimensional stability. The improved hydrolysis stability and oxidative stability of SPI membranes could be attributed to the high basicity of mBAPBDS and flexible main chain of polymer. Methanol permeability test showed that the SPIs membrane had much lower methanol permeability coefficient and thus much higher selectivity （Φ） value compared with Nafion?117 membranes. TheΦvalues of SPIs membranes based on mBAPB and ODA increased to three times as compared with Nafion?117 membranes.The Ic（4/1） and Id（4/1） membranes with high selectivity were used to prepare membrane electrode assembly （MEA）. The performance of MEA was then tested in a DMFC. The results showed the open circuit voltage （OCV） of DMFC equipped with Ic（4/1） and Id（4/1） membranes was higher than that of Nafion?117 membrane, however, their maximal power density was not as good as Nafion?117 membrane because of non-optimized preparation conditions of MEA based on aromatic polymer electrolyte membranes.

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CLC: > Industrial Technology > Electrotechnical > Independent power supply technology (direct power) > Chemical power sources,batteries, fuel cells > Fuel cell
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