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Electrochemical and physicochemical characterization of radiation-grafted membranes for fuel cells

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dc.contributor Aalto-yliopisto fi
dc.contributor Aalto University en
dc.contributor.author Kallio, Tanja
dc.date.accessioned 2012-02-10T08:59:12Z
dc.date.available 2012-02-10T08:59:12Z
dc.date.issued 2003-10-18
dc.identifier.isbn 951-22-6753-5
dc.identifier.uri https://aaltodoc.aalto.fi/handle/123456789/2118
dc.description.abstract This thesis considers alternative proton conducting membrane materials for polymer electrolyte fuel cells (PEFC). The membrane is a key component of the PEFC accounting for the separation of the reactants and allowing the transport of hydrogen ions produced by the anode reaction to the cathode for the cathode reaction while enforcing the electrons to move through the external circuit so that the electrical energy can be utilized. Here the applicability of radiation-grafted membranes in the PEFC with hydrogen or methanol as a fuel has been considered. In particular, the influence of the matrix material of a radiation-grafted membrane on its the behaviour is clarified. The experimental membranes studied were prepared from fluoropolymer films by irradiating with an electron beam, subsequently grafting with styrene and finally sulfonating. Poly(vinylidene fluoride) PVDF, poly(vinylidene fluoride-co-hexafluoropropylene), PVDF-co-HFP, poly(ethylene-alt-tetrafluoroethylene), ETFE and poly(tetrafluoroethylene-co-hexafluopropylene), FEP, were chosen as matrix fluoropolymers. In addition the effect of thickness of the matrix was examined with three PVDF films. Scanning electrochemical microscopy was used as a new tool to investigate proton transport and distribution in the ionically conducting membranes. Such essential membrane properties as conductivity, oxygen permeability, water drag coefficients, methanol permeability, and the actual performance under the fuel cell conditions were found to depend on the crystallinity, or, more precisely, on the water uptake of the membrane, which was higher in membranes with lower crystallinity. The degradation of the side chains ensuring the protonic conductivity was one of the problems restricting the lifetime of the radiation-grafted membranes in the fuel cell with hydrogen as a fuel. However, also the ability of the matrix material itself to withstand this aggressive environment by sustaining the pristine structural arrangement appeared to affect the membrane durability. In general, it appeared that crystallites and a greater matrix thickness brought more strength, provided the matrix did not suffer from phase changes. Using a bis(vinyl phenyl)ethane crosslinker for the PVDF based membranes was detected to protect the side of the membrane facing the anode from chemical degradation. However, no significant improvement in the membrane lifetime was attained due to the degradation of the cathode side of the membrane, with a resulting loss of protonic conductivity. When using methanol as a fuel it was observed that similar performances to commercial materials could be achieved with the radiation-grafted membranes despite of their lower conductivities. This was attributed to the lower methanol permeability of the radiation-grafted membranes due to slower methanol diffusion through the membranes as a consequence of differences in the structures of the membranes. en
dc.format.extent 53, [49]
dc.format.mimetype application/pdf
dc.language.iso en en
dc.publisher Helsinki University of Technology en
dc.publisher Teknillinen korkeakoulu fi
dc.relation.haspart Walsby N., Sundholm F., Kallio T. and Sundholm G., 2001. Radiation-grafted ion-exchange membranes: influence of the initial matrix on the synthesis, structure and non-transport properties. Journal of Polymer Science Part A: Polymer Chemistry 39, pages 3008-3017.
dc.relation.haspart Ericson H., Kallio T., Lehtinen T., Walsby N., Sundholm G., Sundholm F. and Jacobsson P., 2002. Confocal raman spectroscopic investigations of fuel cell tested sulfonated styrene grafted PVDF membranes. Journal of The Electrochemical Society 149, pages A206-A211.
dc.relation.haspart Walsby N., Hietala S., Maunu S. L., Sundholm F., Kallio T. and Sundholm G., 2002. Water in different polystyrene sulfonic acid grafted fluoropolymers. Journal of Applied Polymer Science 86, pages 33-42.
dc.relation.haspart Kallio T., Lundström M., Sundholm G., Walsby N. and Sundholm F., 2002. Electrochemical characterization of radiation-grafted ion-exchange membranes based on different matrix polymers. J. Appl. Electrochem. 32, pages 11-18.
dc.relation.haspart Kallio T., Jokela K., Serimaa R., Ericson H., Sundholm G., Jacobsson P. and Sundholm F., 2003. The effect of fuel cell test on the structure of radiation-grafted ion-exchange membranes based on different fluoropolymers. J. Appl. Electrochem. 33, pages 505-514.
dc.relation.haspart Kallio T., Slevin C., Sundholm G., Holmlund P. and Kontturi K., 2003. Proton transport in radiation-grafted membranes for fuel cells as detected by SECM. Electrochemistry Communications 5, pages 561-565.
dc.subject.other Chemistry en
dc.subject.other Energy en
dc.title Electrochemical and physicochemical characterization of radiation-grafted membranes for fuel cells en
dc.type G5 Artikkeliväitöskirja fi
dc.description.version reviewed en
dc.contributor.department Department of Chemical Technology en
dc.contributor.department Kemian tekniikan osasto fi
dc.subject.keyword proton conductivity en
dc.subject.keyword permeability of reactants en
dc.subject.keyword scanning electrochemical microscopy en
dc.subject.keyword degradation of membranes en
dc.subject.keyword radiation-grafted membranes en
dc.identifier.urn urn:nbn:fi:tkk-000862
dc.type.dcmitype text en
dc.type.ontasot Väitöskirja (artikkeli) fi
dc.type.ontasot Doctoral dissertation (article-based) en
dc.contributor.lab Laboratory of Physical Chemistry and Electrochemistry en
dc.contributor.lab Fysikaalisen kemian ja sähkökemian laboratorio fi

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