Fuel Cell Cutting Edge Center Cubic

Kōtō-ku, Japan

Fuel Cell Cutting Edge Center Cubic

Kōtō-ku, Japan
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Ohkubo T.,Chiba University | Kidena K.,Fuel Cell Cutting Edge Center Cubic | Takimoto N.,Fuel Cell Cutting Edge Center Cubic | Ohira A.,Fuel Cell Cutting Edge Center Cubic
Journal of Molecular Modeling | Year: 2012

We measured the self-diffusion coefficients of water in a Nafion membrane and two sulfonated polyethersulfone (SPES) membranes with varying ion-exchange capacities (IEC) in terms of relative humidity using the pulse field gradient NMR (PFG-NMR) technique. The selfdiffusion coefficients were plotted against the number of water molecules per sulfonic acid group, λ, and compare these values with the results of molecular dynamics (MD) simulations. Classical MD simulations for all membranes were carried out using a consistent force field at λ=3, 6, 9, 12, and 15. The dynamic properties of water (H 2O) and hydronium (H 3O +) on a molecular level were estimated as self-diffusion coefficients and residence times around a sulfonate group (SO - 3 ). The diffusion coefficients of H 2O and H 3O + followed the order, Nafion>SPES with IEC=1.4 >SPES with IEC=1.0>SPES with IEC=0.75, which agreed with the experimental data. The residence time distribution of H 2O around SO - 3 in Nafion was in the range of 1-6 ps, whereas H 2O in the SPES exhibited a residence time of greater than 20 ps. © Springer-Verlag 2011.


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.


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.


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.


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.


Mohamed H.F.M.,Fuel Cell Cutting Edge Center Cubic | Kobayashi Y.,Japan National Institute of Advanced Industrial Science and Technology | Kuroda S.,Fuel Cell Cutting Edge Center Cubic | Ohira A.,Fuel Cell Cutting Edge Center Cubic | Ohira A.,Japan National Institute of Advanced Industrial Science and Technology
Materials Science Forum | Year: 2013

Variations of ortho-positronium (o-Ps) lifetime and gas permeability of the Aquivion® E8705 membrane were studied as functions of temperature under vacuum and relative humidity at room temperature. When the temperature was varied between 0 and 100 °C in vacuum, the hole volume of Aquivion® E8705, deduced from o-Ps lifetime, gradually increased. However, when the relative humidity was changed at room temperature, the hole volume was essentially unchanged. Good linear correlations between the logarithm of permeabilities of O2 and H2 and reciprocal hole volume at different temperatures indicates the importance role of free volume in gas permeation in dry Aquivion® E8705. However, for hydrated Aquivion® E8705 the permeability less depends on hole volume. © (2013) Trans Tech Publications, Switzerland.


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.


Mohamed H.F.M.,Fuel Cell Cutting Edge Center Cubic | Kuroda S.,Fuel Cell Cutting Edge Center Cubic | Kobayashi Y.,Japan National Institute of Advanced Industrial Science and Technology | Oshima N.,Japan National Institute of Advanced Industrial Science and Technology | And 3 more authors.
Physical Chemistry Chemical Physics | Year: 2013

Solutions of Nafion® with an ion exchange capacity (IEC) of 0.91 meq g-1, which are on the verge of the formation of SO3H nanoclusters, were spin coated on silicon (Si), glassy carbon (GC) and platinum/silicon (Pt/Si) substrates to form films of up to 256 nm thickness. Nanostructure of the films was studied using Doppler broadening of annihilation radiation (DBAR), positron annihilation lifetime (PAL), X-ray photoelectron spectroscopy (XPS), an atomic force microscope (AFM) and contact angle measurements. Contact angles as low as 10 degrees indicate that the surface of dry ultrathin Nafion® films on Si is highly hydrophilic. XPS data of 10 nm thick, ultrathin film on Si show that oxygen concentration is enhanced and the SO3H group concentration, in other words, IEC on the surface is much higher than other films. The S parameter measured by DBAR of an ultrathin Nafion® film on Si is much higher than that of the films on the other substrates. We consider that a large number of hydrophilic, reversed micelle like SO3H groups are on the surface of the ultrathin Nafion® film on Si but not on the surface of other films. Positrons implanted into the film are trapped by the SO3H clusters, annihilating with the electrons of oxygen and exhibit the high S parameter. The SO3H concentration on the surface of thin Nafion® films on GC and Pt/Si substrates may not be so high as the threshold for the formation of a large number of SO3H clusters. Positrons implanted into the films annihilate mostly with fluorine atoms, resulting in a low S parameter. The film-substrate interaction plays an essential role in nanostructuring of Nafion® thin films, which may also be the case for Nafion® on the catalysts of polymer electrolyte fuel cells. © 2013 the Owner Societies.


PubMed | Fuel Cell Cutting Edge Center Cubic
Type: Journal Article | Journal: Physical chemistry chemical physics : PCCP | Year: 2013

Solutions of Nafion with an ion exchange capacity (IEC) of 0.91 meq g(-1), which are on the verge of the formation of SO(3)H nanoclusters, were spin coated on silicon (Si), glassy carbon (GC) and platinum/silicon (Pt/Si) substrates to form films of up to 256 nm thickness. Nanostructure of the films was studied using Doppler broadening of annihilation radiation (DBAR), positron annihilation lifetime (PAL), X-ray photoelectron spectroscopy (XPS), an atomic force microscope (AFM) and contact angle measurements. Contact angles as low as 10 degrees indicate that the surface of dry ultrathin Nafion films on Si is highly hydrophilic. XPS data of 10 nm thick, ultrathin film on Si show that oxygen concentration is enhanced and the SO(3)H group concentration, in other words, IEC on the surface is much higher than other films. The S parameter measured by DBAR of an ultrathin Nafion film on Si is much higher than that of the films on the other substrates. We consider that a large number of hydrophilic, reversed micelle like SO(3)H groups are on the surface of the ultrathin Nafion film on Si but not on the surface of other films. Positrons implanted into the film are trapped by the SO(3)H clusters, annihilating with the electrons of oxygen and exhibit the high S parameter. The SO(3)H concentration on the surface of thin Nafion films on GC and Pt/Si substrates may not be so high as the threshold for the formation of a large number of SO(3)H clusters. Positrons implanted into the films annihilate mostly with fluorine atoms, resulting in a low S parameter. The film-substrate interaction plays an essential role in nanostructuring of Nafion thin films, which may also be the case for Nafion on the catalysts of polymer electrolyte fuel cells.

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