Preparation And Characterization Of Composite Proton Exchange Membrane Based On Sulfonated Poly (Arylene Ether Sulfone)

Polymer electrolyte membrane fuel cells (PEMFC) have attracted considerableattention as candidates for alternative power sources due to their high power density,good energy conversion efficiency, and zero emissions levels. As the core component,proton exchange membrane, has become the focus of the related researches forimprovement of PEMFC performance. Different kinds of sulfonated polymers weresynthesized and casted to membranes. However, most of those pristine membranescouldn’t meet the balanced overall performance requirements of applicable protonexchange membrane for the presence of respective functional defects. Sulfonated poly(arylene ether sulfone)s (SPAESs), as a kind of novel polymer electrolytes, arecomparative cheaper and easier to prepare. The good proton conductivity, thermal andmechanical properties of SPAESs make them as alternative proton exchangemembranes for fuel cells. However, the poor oxidative stability and excessiveswelling ratio of SPAESs bring limitations for their further use. The dimensional andoxidative stability of SPAESs proton exchange membranes are crucial issues thatrequire improvement through suitable modification method.In this thesis, three kinds of SPAES with varied chemical composition werecharacterized and compared with each other in order to understand the relationshipbetween the structure and perfermance.Then, one of SPAES with fluoropheny sidegroup was selected to prepare composite membranes by different methods, includingblending with PAN and polybenzoxazoles(PBO) nanofiber membranes in target tosolve the problem of excessive swelling ratio. What’s more, a kind of SPAEScomposite membrane has outstanding oxidative stability was prepared bycompounding SPAES nanofiber membrane with Nafion resign. The main content ofthe thesis is as follow:1. The performance of three SPAESs in different chemical structure wascharacterized and compared with each other. Three SPAESs with similar backbone butvaried side groups, that is, with fluoropheny side group (SEF), cyanogroupson sidegroup (SEB) and without any side group introduction (SES), were investigated byproperties comparison and their membranes equipped MEA measurement. Theintroduction of fluoropheny and cyanogroupson to SPAES could change the micro phase separation due to electron repulsive force and cross-linking action, respectively.Smaller and more uniform hydrophobic domains are formed in SEF and SEB than thatin SES. In addition, SEF shows the smallest hydrophobic phase and inter-connectedhydrophilic phase, which lead to high water uptake and excellent single cellperformance. The maximum power density of the SEF MEA and SEB MEA reached115.5mw/cm2and94.7mw/cm2compared to72.5mw/cm2for SES MEA. Therefore,we conclude that the introduction of suitable side group to sulfonated poly (aryleneether sulfone) might contribute to its overall performance as one of candidatematerials for proton exchange membrane.2. A series of SEF/PAN blend membranes (SPs) with excellent dimensionalstability and proton conductivity were successfully prepared by casting. Targeted ateasing the excessive swelling ratio, SPs were prepared from their blend solutions indifferent ratio. The corporation of PAN into SPAES could reduce the water uptake andimprove the oxidative stability of the obtained membranes compared with the pristineSPAES membrane. That the PAN phase distributed as separated domains in SPAESmatrix was found, the interaction between SPAES and PAN may be present, which isresponsible for the improvement of dimensional and oxidative stability. Although theproton conductivity of the blend membranes became reduced with increase of PANcontent in the SPAES/PAN blend, the conductivity of0.0265S/cm at30oC could stillbe reached, satisfying the requirement for proton exchange membrane Fuel Cell.3. A series of SEF/PBO multilayer membranes were successfully prepared bypore-filling method based on PBO nanofiber membrane.PBO nanofiber membraneexhibit its potential to be used as support material in proton exchange membrane byits excellent mechanical strength and dielectric property. The multilayer membraneshave excellent dimensional stability. The swelling ratio value of SP7.8%is12.6%at80oC, while the pristine SEF membrane can reach to60.9%.Compared to othertraditional way to improve the dimensional stability of SPAESs, the advantage ofcorporation of PBO nanofiber membrane lies on no loss of water uptake capacity onthe resulting composite membrane, which promise the only slightly decrease on theproton conductivity.4. A series of anti-oxidative Nafion/SEF nanofiber enhanced compositemembrane (NSs) were successfully prepared. In this chapter, the poor oxidativestability of SEF was improved by composite its nanofiber membranes with Nafionresign which has good oxidative stability.SEF nanofiber membrane could be obtainedby the method of electro-spinning, then it was composited with Nafion resign. TheSEM figures show the porous structure of SEF nanofiber and solid cross-sectionalarea of NSs, respectively. The performance tests show the improvement of anti-oxidation ability of NSs compared to the pristine SEF membrane. Compare to pristineNafion membrane, NSs have better mechanical strength and higher water uptakecapacity, reached28.2%at80oC.