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Author: Gursel, Selmiye AlkanCOAR Access Rights: metadata only access

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    Citation - WoS: 24
    Citation - Scopus: 28
    Enhancing Proton Conductivity Via Sub-Micron Structures in Proton Conducting Membranes Originating From Sulfonated Pvdf Powder by Radiation-Induced Grafting
    (Elsevier Science Bv, 2018) Sadeghi, Sahl; Sanli, Lale Isikel; Guler, Enver; Gursel, Selmiye Alkan
    We report here submicron-structured proton conducting poly(vinylidene fluoride)-graft-poly(styrene sulfonic acid) (PVDF-g-PSSA) membranes for polymer electrolyte membrane fuel cells (PEMFC). Highly conductive proton exchange membranes were obtained by single-step radiation grafting of sodium styrene sulfonate (SSS) to powder-form PVDF, followed by casting and subsequent solvent evaporation. The obtained submicron structure of membrane through solvent evaporation led to the arrangement of ionic channels proving increasing proton conductivity with the increase in graft level. In addition, a temperature above melting point of PVDF was used for solvent evaporation to allow melted PVDF to fill the formed pores, providing denser structure resulting in improved mechanical properties of the membranes. SSS grafting to PVDF powder was verified by NMR spectroscopy, and resultant membranes were characterized for proton conductivity, water up-take, morphology, mechanical and thermal properties, and fuel cell performance. According to preliminary tests, proton conductivities which were observed to increase with graft level were found to be around 70 mS cm(2) at 35% graft level. Thus, this led to a promising power density of 250 mW/cm(2) at 650 mA/cm(2).
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    Article
    Citation - WoS: 11
    Citation - Scopus: 13
    Characterization and Fuel Cell Performance of Divinylbenzene Crosslinked Phosphoric Acid Doped Membranes Based on 4-Vinylpyridine Grafting Onto Poly(ethylene-Co Films
    (Pergamon-elsevier Science Ltd, 2018) Guler, Enver; Sadeghi, Sahl; Gursel, Selmiye Alkan
    The effect of divinylbenzene (DVB) as crosslinker on the graft polymerization of 4-vinylpyridine (4VP) from poly(ethylene-co-tetrafluoroethylene) (ETFE) films was studied. The resulted films were doped with phosphoric acid (PA) and characterized for mechanical, surface, thermal properties, and fuel cell performance. The crosslinked membrane obtained from grafting a mixture of 4VP with 1% DVB improved the polymerization kinetics and resulted in about 50% graft level depending on graft conditions. The crosslinked membranes were also found to have better mechanical properties compared to its non-crosslinked counterpart. The resulted membrane exhibited proton conductivity as high as 75 mS/cm under 50% relative humidity (RH) at 120 degrees C, besides almost doubling the power output of fuel cell compared to a non-crosslinked membrane. To the best of our knowledge, DVB crosslinked 4VP based ETFE membranes were, for the first time, tested in practical fuel cell test station correlating their performance to operating temperature. Furthermore, surface properties of produced membranes were additionally correlated to the degree of crosslinking. Humidity dependence is less pronounced in the produced membranes resulting in strong potential for testing at intermediate temperature (80-120 degrees C) polymer electrolyte membrane fuel cells. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.