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Studies on Sulfonated Polysulfone/Inorganics Hybrid Proton Exchange Membranes

Author: FeiGuoPing
Tutor: ZhaoJiongXin
School: Donghua University
Course: Materials Physics and Chemistry
Keywords: Sulfonated polysulfone phosphotungstic acid silica organic-inorganic proton exchange membrane
CLC: TM911.4
Type: Master's thesis
Year: 2009
Downloads: 138
Quote: 1
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Abstract


Proton exchange membrane fuel cells（PEMFCs）are of enormous interest as potential power sources in view of their high-energy efficiency,low pollution levels and quietness.A proton exchange membrane（PEM）is the key component for PEMFC. The perfluorosulfonic acid（PFSA）PEM,represented by Nafion,possesses high proton conductivity,good chemical stability and long useful lifetime.However,the PFSA membrane is too expensive and its proton conductivity decreases obviously when operated upon 90℃due to dehydration,which greatly limit its applications.In recent years,kinds of non-fluoro polymers with good thermal and mechanical stabilities have been used as PEM materials.In this thesis,Sulfonated polysulfone （SPSU）was synthesized via a solution sulfonation method.SPSU was modified with inorganic particles such as phosphotungstic acid（PWA）and silica（SiO2）,to prepare a high efficiency and low cost organic-inorganic hybrid proton exchange membranes with excellent proton conductivity and low methanol permeability.The structures and properties of the hybrid membranes were also studied.Sulfonated polysulfone with different sulfonation degree（DS）was prepared via a solution sulfonation method using mixtures of chlorosulfonic acid and chlorotrimethylsilane as sulfonating agent and 1,2-dichloroethane as solvent.Fourier transform infrared analysis confirmed that sulfonic acid groups were introduced into the SPSU chain successfully.DS had a great influence on SPSU membrane properties. The water uptake,swelling ratio and hydration coefficient of SPSU proton exchange membranes with DS＞50%increased abruptly,but increased slowly with DS＜50%. The conductivity of SPSU membranes with DS=53%was 0.024S·cm-1 at 80℃, which was in the range needed for high performance fuel cell PEM.SPSU/PWA hybrid proton exchange membranes were prepared with SPSU as matrix.The influence of PWA content on the properties of the hybrid membranes, such as proton conductivity,chemical stability,methanol permeability,PWA extraction,water uptake and mechanical property,was studied in detail.FT-IR spectroscopy of the hybrid membranes exhibited band shifts showing a possibility of intermolecular hydrogen bonding interaction between sulfonic acid groups and PWA molecules.After incorporation of PWA particles,the proton conductivity of the hybrid membranes was enhanced as expected,but lowering methanol barrier property and chemical stability.The proton conductivity of SPSU/PWA hybrid membranes with from 0 to 30 wt.%PWA was increased from 0.024 S·cm-1 to 0.166 S·cm-1 at 80℃,while the methanol permeability increased from 7.12×l0-7cm2·s-1 to 1.83×10-6cm2·s-1.The extraction of PWA from the hybrid membranes was strongly depended on the DS of polymer matrix.Interestingly,the hybrid membrane with high DS had a relatively lower PWA extraction.The PWA extractions from SPSU/PWA hybrid membranes with 10%,53%and 86%DS were 10.1%,4.6%and 3.8%, respectively,after 72h hot water treatment.These phenomena further indicated that there was a strong interaction between the sulfonic acid groups and PWA molecules.SPSU/PWA/SiO2 organic-inorganic hybrid proton exchange membranes were prepared with SPSU as matrix.The influence of silica content on the structures and properties of the hybrid membranes was also studied in detail.SEM showed that SiO2 and PWA nanoparticles were uniformly distributed over the membrane and did not form any agglomerations when SiO2 content was below 2.0 wt.%.The size of SiO2 and PWA particles was observed to be around 30nm.The silica particles in the hybrid membrane containing above 2.0 wt.%silica content showed less uniformity in their distribution,and aggregations of some micron were formed,which would become larger and more continuous with silica content increasing.After incorporation of SiO2 particles,it was effective in enhancing chemical stability,methanol barrier property and PWA stability in the membrane,whereas excessive silica content caused a large aggregation of SiO2 particles,leading to the deterioration of membrane properties. The study displayed that the SPSU/PWA/SiO2 hybrid membranes with 2 wt.%silica content showed the best results:the proton conductivity and methanol permeability were 0.166s·cm-1 and 7.82×10-7 cm2·s-1,respectively,which was better than that of Nafion117 with proton conductivity of 0.135s·cm-1 and methanol permeability of 9.67×10-6cm2·s-1 under the same condition.And the hybrid membrane owned the lowest PWA extraction and best chemical stability.

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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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