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Masayasu Tasaka – One of the best experts on this subject based on the ideXlab platform.

  • Thermoosmosis and Transported Entropy of Water across Hydrocarbonsulfonic Acid-Type Cation-Exchange Membranes
    Bulletin of the Chemical Society of Japan, 1995
    Co-Authors: Takashi Suzuki, Keiko Iwano, Ryotaro Kiyono, Masayasu Tasaka

    Abstract:

    Solvent transport across hydrocarbonsulfonic acid-type cation-exchange membranes was measured for aqueous electrolyte solutions under a temperature difference and an osmotic pressure difference. The hydrocarbonsulfonic acid-type cation-exchange membranes, Aciplex® K-181, Aciplex® K-182, and Neosepta® C66-5T with the H+, Li+, Na+, K+, NH4+, CH3NH3+, (CH3)2NH2+, (CH3)3NH+, (CH3)4N+, (C2H5)4N+, (n-C3H7)4N+, and (n-C4H9)4N+ forms were used. The direction of thermoosmosis across the membranes with the H+ and the Na+ forms was from the cold side to the hot side, as observed for various anion-exchange membranes. However, the direction was from the hot side to the cold side for the membranes with the ammonium and the alkylated ammonium ion forms, except for Neosepta® C66-5T with the (CH3)4N+, (C2H5)4N+, and (n-C3H7)4N+ forms. This is why the entropy of the water in the membranes will increase with increasing the number of hydrogens combining with the nitrogen of the alkylated ammonium counterions, because they ar…

  • Solvent transport across anion-exchange membranes under a temperature difference and transported entropy of water
    Journal of Membrane Science, 1994
    Co-Authors: Takashi Suzuki, Ryotaro Kiyono, Masayasu Tasaka

    Abstract:

    Abstract Solvent transport across anion-exchange membranes was measured for aqueous KF, KCl, KNO 3 (or NaNO 3 ), KIO 3 , HCOONa, CH 3 COONa (or K), C 6 H 5 COONa, C 6 H 5 SO 3 Na and p -CH 3 C 6 H 4 SO 3 Na solutions under a temperature difference and an osmotic pressure difference. Hydrocarbon-type anion-exchange membranes Neosepta® AM-1, Aciplex® A-201 and A-221, test membranes STA-1 to STA-5, and fluorocarbon-type anion-exchange membrane Tosflex® IE-DF 17 were used. The water content is represented by the unit: g H 2 O per g dry membrane without the weight of anhydrous counterions. Plots of the volume flux against the temperature difference of both side solutions gave straight lines starting from zero. The direction of thermoosmosis was from the cold to the hot side. The order of water content of membranes is F − >IO − 3 >Cl − >NO − 3 for inorganic ions and CH 3 COO − >HCOO − >C 6 H 5 COO − > p -CH 3 C 6 H 4 SO − 3 (or C 6 H 5 SO − 3 ) for organic ions regardless of the type of membrane. The order of the absolute value of the entropy difference between transported entropy in membranes and partial molar entropy of water in the external solutions is IO − 3 >F − >Cl − >NO − 3 for inorganic ions and C 6 H 5 COO − >CH 3 COO − >HCOO − for organic ions for all membranes.

  • Thermal membrane potential across test anion-exchange membrane Aciplex STA and the transported entropy of counterions.
    membrane, 1993
    Co-Authors: Kokichi Hanaoka, Masayasu Tasaka, Ryotaro Kiyono, Masato Hamada, Kiyotaka Yoshie

    Abstract:

    An improved thermal membrane potential cell was constructed with blocks of poly (vinyl chloride). In the new cell the membrane was used as a ribbon with the two contacts to the external solutions on opposite sides and separated by 0 to 10 mm. Thermal membrane potentials across test anion-exchange membranes Aciplex STA-1 to 5, of which the thickness is about 0.1 mm, were measured using the new cell. The transported entropy of counterions in the membranes was estimated from experimental data for thermal membrane potential, electroosmosis and thermoosmosis. Thermal membrane potentials across STA-2 to 5 were nearly equal to each other regardless of the differences in the water content, the ion-exchange capacity and the DVB content. However, the difference between the mean molar transported entropy of counterions and the partial molar entropy of the ions in the external solutions (s_-s_), which reflects to the stability of counterions in the membrane, decreases roughly with decrease in the water content or with increase in the molality of fixed charges in the membrane. The absolute values of thermal membrane potentials across STA-3 increased in the order of I->Cl-≈Br->IO3->F-≈CH3COO- ion forms.

Bruno Ameduri – One of the best experts on this subject based on the ideXlab platform.

  • Recent Advances on Fluoromembranes for Fuel Cell
    , 2012
    Co-Authors: Bruno Ameduri

    Abstract:

    Fuel cell can be regarded as potential future alternative source of green Energy. Polymer electrolyte membrane fuel cell (PEMFC) is composed of an electrolyte (usually a membrane which must be an ionic conductor) located between with anode and the cathode. The membrane is a functional polymer which bears protonic, cationic or anionic groups depending on the choice of use and must fulfill drastic requirements. Fluorinated polymers [1] that possess protogen groups are suitable candidates from various strategies: -either by ” direct ” radical copolymerization of fluoroolefins bearing protogen groups; that strategy has already led to various commercially available products such as Nafion, Flemion, 3M Membrane, Hyflon Ion, Aciplex and others. -or by chemical modifications fluoropolymers. To overcome issues of thermal stability (> 90 °C) and low relative humidity (HR < 30 %) various challenges for the development of protonic PEMFCs will be proposed.

  • Fluorofunctional Copolymers as Polymer Electrolyte Membranes for Fuel Cells
    , 2009
    Co-Authors: Bruno Ameduri

    Abstract:

    Fluorinated functional polymers (1) exhibit remarkable properties (thermal and oxidative stabilities, chemical inertness, low refractive index, good surface properties, etc) that enable them to find numerous applications in high tech fields: aerospace, energy, automotive industries, optics, microelectronics, and engineering. Fluoropolymers for energy are nowadays seeing an enormous growth in both their number and variety. Although most membranes for fuel cells are made from perfluorosulfonic acid polymers such as Nafionâ, Flemionâ, Hyflonâ, Fumionâ, 3MâMembranes, or Aciplexâ, produced from the radical copolymerization of tetrafluoroethylene with aliphatic perfluorinated vinyl ethers, few have been achieved from aromatic functional fluoropolymers. The objective of this presentation deals with the syntheses of new generations of original membranes prepared from aromatic and aliphatic fluorinated copolymers incorporating fluoromonomers such as vinylidene fluoride (VDF, F2C=CH2), hexafluoropropene (HFP, F2C=CFCF3), and an aromatic fluorinated monomer functionalized by a sulfonic acid, or -trifluoromethacrylic acid (MAF). However, membranes from perfluorosulfonic acids suffer from high cost, methanol crossover and they usually show a high drying when the membrane is used at temperatures higher than 80 °C, hence undergoing severe damages. It is urgent to find out other systems which do not require any water and imidazole ring can play a suitable role thanks to potential jumps of proton from donor to acceptor nitrogenated sites. A further strategy deals with the synthesis of original alternated poly(CTFE-alt-VE) copolymers2 (where CTFE and VE stand for chlorotrifluoroethylene and vinyl ether, respectively). After reporting the synthesis of the monomer (A) and the copolymer (B), the molecular weights and the thermal properties (Tg and Tdec) of which are listed, various membranes prepared by casting will be characterized. First, the thermal properties followed by the electrochemical properties: the conductivity values reached up to 14 mS.cm-1 according to the temperature and the relative humidity. 1. B. Améduri B. Boutevin, Well Architectured Fluoropolymers: Synthesis, Properties and Applications, Elsevier, Amsterdam, 2004 2. L. Delon, B. Améduri, B. Boutevin, D. Jones, J. Rozière, G. Frutsaert, X. Glipa World Patent WO2007/141441 2007-12-13 (assigned to Peugeot Citroën/CNRS).

  • Functional fluoropolymers for fuel cell membranes
    Solid State Ionics, 2005
    Co-Authors: Renaud Souzy, Bruno Ameduri, Bernard Boutevin, Gérard Gebel, Philippe Capron

    Abstract:

    Abstract Various routes to synthesise functional fluoropolymers used in membranes for fuel cell applications are presented. They can be separated into three main families of alternatives. The first concerns the direct radical copolymerisation of fluoroalkenes with fluorinated functional monomers. The latter are either fluorinated vinyl ethers, α,β,β-trifluorostyrenes or trifluorovinyl oxy-aromatic monomers bearing sulfonic or phosphonic acids. The resulting membranes are the well-known Nafion®, Flemion®, Hyflon®, Dow®, Aciplex® or BAM3G®. The second way deals with the chemical modification of hydrogenated polymers (e.g., polyparaphenylenes) with fluorinated sulfonic acid synthons. The third possibility concerns the synthesis of FP-g-poly(M) graft copolymers (where FP and M stand for fluoropolymer and monomer, respectively) obtained by activation (e.g., by irradiation with electrons, γ-rays or ozone) of fluoropolymers, followed by grafting of the monomers. The most used M is styrene, and a further step of sulfonation was achieved onto FP-g-PS, leading to FP-g-PS sulfonic acid graft copolymers.

Arun Venkatnathan – One of the best experts on this subject based on the ideXlab platform.

  • Molecular dynamics simulations of side chain pendants of perfluorosulfonic acid polymer electrolyte membranes
    J. Mater. Chem. A, 2013
    Co-Authors: Anurag Prakash Sunda, Arun Venkatnathan

    Abstract:

    Perfluorosulfonic acid (PFSA) polymer electrolyte membranes like Dow, Aciplex and Nafion have similar backbones but different side chain pendants. The effect of hydration and temperature on the side chain pendant nanostructure, and water and hydronium ion dynamics, are investigated by employing classical molecular dynamics simulations at 300 K and 350 K. The 60% longer side chain pendant length in Aciplex compared to Dow results in phase segregation. The presence of an extra ether oxygen atom in the Nafion side chain pendant provides more flexibility (∼20% chain length contraction caused by flexibility and the hydrophobic force of the pendant CF3 group) where the sulfonate group tends to drift from the hydrophilic–hydrophobic domain, which gives rise to a hydrosphere region at higher hydration. The calculated structure factors and scattering intensities reproduce features of SANS and SAXS profiles for Dow and Nafion, and confirm the existence of spherical water aggregates in the rod shaped pendant nanostructure of Nafion. The effect of hydration on the mobility of hydronium ions at 300 K in Nafion is insignificant at higher hydration (λ ≥ 9), and trends are in agreement with experimental data. The activation energy of the diffusion of hydronium ions and water molecules in Nafion side chain pendant–water mixtures (14–25 kJ mol−1) validate experimental observations (16–22 kJ mol−1).

  • Atomistic simulations of structure and dynamics of hydrated Aciplex polymer electrolyte membrane
    Soft Matter, 2012
    Co-Authors: Anurag Prakash Sunda, Arun Venkatnathan

    Abstract:

    Aciplex is a perfluorosulfonic acid (PFSA) polymer electrolyte membrane, where its efficiency depends on hydration and temperature. In the present work, the nanostructure of the Aciplex membrane and transport of hydronium ions and water molecules are characterized using classical molecular dynamics simulations at varying hydrations and temperatures. An examination of radial distribution functions and scattering intensities shows that temperature has a negligible effect on membrane nanostructure at all hydration levels. The calculated structural factors and scattering intensities of water molecules closely resemble the experimental SAXS and SANS features of PFSA membranes. Further, for all hydration, the strong interactions between sulfonate groups of the pendant side chain arise only from inter-chain interactions. The stiffness of a pendant side chain limits the possibility of intra-chain interactions between sulfonate groups. The distance between adjacent sulfonate groups shows a variation of 3 A from an average distance of 25 A which shows a suitable orientation of the pendant side chain to maximize water–hydronium interactions with the sulfonate group. The radius of gyration shows an insignificant change with hydration and temperature which demonstrates that the membrane is a suitable electrolytic component for PEM fuel cells. The calculated diffusion coefficients of hydronium ions and water molecules are found to be in reasonable agreement with experimental data. The enlarged hydrophobic domains assisted by the rigid pendant side chain in a hydrated Aciplex membrane results in lower mobility of water molecules compared to Nafion.