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Mohamed H.F.M.,Minia University | Abdel-Hady E.E.,Minia University | Ohira A.,Fuel Cell Cutting Edge Center Cubic
Journal of Physics: Conference Series | Year: 2015

The mechanism of gas permeation in per-fluorinated sulfonic acid/PTFE copolymer Fumapem® membranes for polymer electrolyte fuel cells has been investigated from the viewpoint of free volume. Three different samples, Fumapem® F-950, F-1050 and F-14100 membranes with ion exchange capacity (IEC) = 1.05, 0.95 and 0.71 meq/g, respectively were used after drying. Free volume was quantified using the positron annihilation lifetime (PAL) technique and gas permeabilities were measured for O2 and H2 as function of temperature. Good linear correlation between the logarithm of the permeabilities at different temperatures and reciprocal free volume indicate that gas permeation in dry Fumapem® is governed by the free volume. Nevertheless permeabilities are much smaller than the corresponding flexible chain polymer with a similar free volume size due to stiff chains of the perfluoroethylene backbone. © Published under licence by IOP Publishing Ltd. Source


Ohira A.,Fuel Cell Cutting Edge Center Cubic | Ohira A.,Japan National Institute of Advanced Industrial Science and Technology | Kuroda S.,Fuel Cell Cutting Edge Center Cubic | Mohamed H.F.M.,Fuel Cell Cutting Edge Center Cubic
ECS Transactions | Year: 2012

To study the property of proton conduction for electrolyte thin film inside catalyst layer, model ionomer thin films were prepared on different surfaces such as carbon and platinum substrates. An atomic force microscopy coupled with electrochemical technique (e-AFM) demonstrated that proton conduction reduced with film thickness, and abruptly decreased when film thickness was less than 10 nm for both carbon and platinum substrate. This indicates that number of active proton conductive pathway and/or connectivity of proton path network change with film thickness, and is though that the morphology of thin film is essentially different from that of a bulk membrane. © The Electrochemical Society. Source


Mohamed H.F.M.,Fuel Cell Cutting Edge Center Cubic | Mohamed H.F.M.,Minia University | Kuroda S.,Fuel Cell Cutting Edge Center Cubic | Kobayashi Y.,Japan National Institute of Advanced Industrial Science and Technology | And 3 more authors.
Materials Science Forum | Year: 2013

Nafion® is one of the most popular proton conducting membranes for polymer electrolyte fuel cells (PEFCs). For the integration of Nafion® to the catalyst layers, very thin layers of the polymer are often formed on the catalysts of PEFC from dilute solutions. We applied energy variable positron annihilation to characterizing the structure of thin Nafion® films prepared by spin and dip coating from ethanol/water solutions of Nafion® on Si substrates. Experimental data suggest that the nanostructure of 23 nm thick spin coated Nafion® film is different from 220 nm thick film and also from 26 and 227 nm thick dip coated films, possibly due to the preservation of the unique rod-like structure of Nafion® in the dilute solution.© (2013) Trans Tech Publications, Switzerland. Source


Mohamed H.F.M.,Fuel Cell Cutting Edge Center Cubic | Mohamed H.F.M.,Minia University | Kobayashi Y.,Japan National Institute of Advanced Industrial Science and Technology | Kuroda C.S.,Fuel Cell Cutting Edge Center Cubic | And 2 more authors.
Macromolecular Chemistry and Physics | Year: 2011

The ortho-positronium (o-Ps) lifetime was measured as a function of temperature for the perfluorinated PEMs Nafion NR212 and Aquivion E8705. The o-Ps lifetime in Aquivion E8705 was found to be shorter than Nafion NR212 in the entire temperature range studied. Abrupt changes in the temperature coefficient of the o-Ps lifetime were noticed and the α-relaxation, β-relaxation, and stress relief temperatures were identified. It turned out that Aquivion E8705 has higher α-relaxation and stress relief temperatures than Nafion NR212. Dissociation of the ionic clusters and large change in the nanostructure after heating to 160°C were observed for Nafion NR212 but not for Aquivion E8705. It is demonstrated that Aquivion E8705 has a higher thermal stability than Nafion NR212.(Figure Presented) © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Mohamed H.F.M.,Fuel Cell Cutting Edge Center Cubic | Mohamed H.F.M.,Minia University | Kobayashi Y.,Japan National Institute of Advanced Industrial Science and Technology | Kuroda S.,Fuel Cell Cutting Edge Center Cubic | And 2 more authors.
Chemical Physics Letters | Year: 2012

The behavior of positrons that do not form positronium in dry fluorinated polymer electrolyte membranes (Nafion®, Fumapem® and Aquivion®) with various ion exchange capacities (IECs) was studied by the combined use of Doppler broadening of annihilation radiation (DBAR) and the positron lifetime technique. The drastic increase of the S parameter, measured by DBAR, with increasing IEC above 0.91 meq/g indicates that increasing numbers of positrons are trapped by oxygen atoms and annihilate with the electrons bound in them. Reversed micelle like SO 3H nanoclusters to trap positrons possibly appear at IEC = 0.91 meq/g and their concentration increases with increasing IEC. © 2012 Elsevier B.V. All rights reserved. Source

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