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Shimshon Gottesfeld - One of the best experts on this subject based on the ideXlab platform.

  • electro osmotic drag of water in poly Perfluorosulfonic Acid membranes
    Journal of The Electrochemical Society, 2001
    Co-Authors: Shimshon Gottesfeld
    Abstract:

    Direct methanol fuel cells (DMFCs) using poly(Perfluorosulfonic Acid) membranes were used to determine the water electro-osmotic drag coefficients in these ionomeric membranes. In a DMFC fed with 1.0 M aqueous methanol at the anode and dry O 2 at the cathode, the ionomeric membrane can he fully equilibrated on both sides with liquid water at a sufficiently high current density. In this special situation, the water flux across the membrane from anode to cathode is driven by protonic drag exclusively. From measurements performed on Nafion®, C®, and Dow® membranes, water drag coefficients of all membranes increase with temperature. Compared with a fully hydrated membrane, a dried membrane (105°C in vacuum) known to have a lower water content has a lower water drag coefficient. For a series of Nafion membranes (including C membrane), a membrane with a higher equivalent weight has a lower water drag coefficient. The water drag coefficient of a Dow membrane is unusually low compared to that of a Nafion membrane of similar equivalent weight. These trends of water drag coefficients may correlate with the membrane structure and water content. Implications of these results on water management in polymer electrolyte fuel cells are discussed.

  • high performance direct methanol polymer electrolyte fuel cells
    Journal of The Electrochemical Society, 1996
    Co-Authors: Xiaoming Ren, Mahlon S Wilson, Shimshon Gottesfeld
    Abstract:

    Direct methanol fuel cells (DMFCs) using Pt‐Ru electrocatalysts and Perfluorosulfonic Acid membranes provide high performances if operated above 100°C with optimized catalyst layers. A decal transfer method is used to apply thin‐film catalyst/ionomer composite layers to Nation® membranes. A Nation 112 membrane/electrode assembly operating on 5 atm oxygen at 130°C yields a current of 670 mA/cm2 at 0.5 V cell voltage. Peak power density is 400 mW/cm2. The same cell operating on 3 atm air at 110°C yields 370 mA/cm2 at 0.5 V and provides a maximum power density of 250 mW/cm2.

  • high performance direct methanol polymer electrolyte fuel cells
    Journal of The Electrochemical Society, 1996
    Co-Authors: Xiaoming Ren, Mahlon S Wilson, Shimshon Gottesfeld
    Abstract:

    Direct methanol fuel cells (DMFCs) using Pt-Ru electrocatalysts and Perfluorosulfonic Acid membranes provide high performances if operated above 100 C with optimized catalyst layers. A decal transfer method is used to apply thin-film catalyst/ionomer composite layers to Nafion{reg_sign} membranes. A Nafion 112 membrane/electrode assembly operating on 5 atm oxygen at 130 C yields a current of 670 mA/cm{sup 2} at 0.5 V cell voltage. Peak power density is 400 mW/cm{sup 2}. The same cell operating on 3 atm air at 110 C yields 370 mA/cm{sup 2} at 0.5 V and provides a maximum power density of 250 mW/cm{sup 2}.

  • a comparative study of water uptake by and transport through ionomeric fuel cell membranes
    Journal of The Electrochemical Society, 1993
    Co-Authors: Thomas Zawodzinski, Roger Jestel, Cruz Lopez, Judith Valerio, T. E. Springer, John Davey, Shimshon Gottesfeld
    Abstract:

    Water uptake and transport parameters measured at 30 C for several available Perfluorosulfonic Acid membranes are compared. The water sorption characteristics, diffusion coefficient of water, electroosmotic drag, and protonic conductivity were determined for Nafion 117, Membrane C, and Dow XUS 13204.10 developmental fuel cell membrane. The diffusion coefficient and conductivity of each of these membranes were determined as functions of membrane water content. Experimental determination of transport parameters, enables one to compare membranes without the skewing effects of extensive features such as membrane thickness which contributes in a nonlinear fashion to performance in polymer electrolyte fuel cells.

  • characterization of polymer electrolytes for fuel cell applications
    NASA STI Recon Technical Report N, 1992
    Co-Authors: Thomas Zawodzinski, T. E. Springer, Francisco A Uribe, Shimshon Gottesfeld
    Abstract:

    Abstract We review here our recent work on polymer electrolyte fuel cells emphasizing membrane transport issues. Transport parameters measured at 30°C for several available Perfluorosulfonic Acid membranes are compared. The diffusion coefficient and conductivity of each of these membranes were determined as functions of membrane water content. Data on water sorption and conductivity are reported for an experimental membrane which is a modified form of NAFION®. Contact angle measurements indicate that the surface of a Perfluorosulfonic Acid membrane exposed to water vapor is quite hydrophobic, even in the presence of saturated water vapor. Modeling of water distribution in PEFCs based on the uptake and transport data shows that membrane thickness contributes in a nonlinear fashion to performance in PEM fuel cells.

Masahiro Watanabe - One of the best experts on this subject based on the ideXlab platform.

  • effects of short side chain Perfluorosulfonic Acid ionomers as binders on the performance of low pt loading fuel cell cathodes
    Journal of Power Sources, 2015
    Co-Authors: Youngchul Park, Masahiro Watanabe, Katsuyoshi Kakinuma, Hiroyuki Uchida, Makoto Uchida
    Abstract:

    Abstract We investigated the effects of short-side-chain (SSC) Perfluorosulfonic Acid ionomers on the electrochemical properties, fuel cell performance and ionomer distribution of a highly dispersed Pt/GCB catalyst with a low Pt loading, 0.05 mg cm−2. The SSC ionomers in the cathode catalyst layers (CLs) resulted in an improvement of the Pt utilization (UPt) and Pt effectiveness (EfPt) values compared with those for the conventional long-side-chain (LSC) ionomer. Furthermore, the SSC ionomers with high ion exchange capacity (IEC), e.g., SSC-1.43 and SSC-1.80 ionomers, exhibited significantly enhanced cell performance under low to medium relative humidity (RH) conditions. This result is ascribed to the higher proton conductivity of the SSC ionomers and more effective trapping of water that is produced during the oxygen reduction reaction (ORR) than those of the LSC ionomer. It was also found that the SSC ionomers showed better continuity and uniformity on the Pt and carbon particles than the LSC ionomer, which might have led to improvement of both the mass transport and the proton-conducting network in the CLs. The application of the SSC ionomers as binders demonstrated an increase of the performance at the low Pt loading fuel cell cathode over a wide range of humidity.

  • aromatic ionomers with superAcid groups
    Chemical Communications, 2009
    Co-Authors: Kenji Miyatake, Takuya Shimura, Takefumi Mikami, Masahiro Watanabe
    Abstract:

    Aromatic polymers containing Perfluorosulfonic Acid groups show well-developed and interconnected ionic clusters, and thus high proton conductivity at wide humidity range.

  • decomposition mechanism of Perfluorosulfonic Acid electrolyte in polymer electrolyte fuel cells
    Electrochemistry Communications, 2006
    Co-Authors: Makoto Aoki, Hiroyuki Uchida, Masahiro Watanabe
    Abstract:

    Decomposition behavior of Perfluorosulfonic Acid (PFSA) electrolytes caused by the crossover of H2 or O2 in PEFCs was evaluated at 80 °C with a newly proposed method. Two gas-diffusion electrodes, consisting of Pt catalysts supported on carbon black and Nafion® ionomer, were mounted in a fuel cell housing with and without Nafion® membrane. Mixed gas of H2 and air with a constant composition was supplied to the cell, simulating crossover to an anode or a cathode. The F− emission rates increased with increasing the relative humidity in both H2-rich and O2-rich conditions, probably due to the enhanced penetration of H2O2, and/or the relating radical in swollen electrolyte. It was found that an appreciable fraction of H2O2 or OH radical was easily scavenged at Pt particles in the catalyst layer or in the Pt-dispersed Nafion®, resulting in the suppressed F− emission rates. Degradation mechanism of PFSA electrolytes was discussed.

  • Decomposition mechanism of Perfluorosulfonic Acid electrolyte in polymer electrolyte fuel cells
    Elsevier, 2006
    Co-Authors: Makoto Aoki, Hiroyuki Uchida, Masahiro Watanabe
    Abstract:

    Decomposition behavior of Perfluorosulfonic Acid (PFSA) electrolytes caused by the crossover of H2 or O2 in PEFCs was evaluated at 80 °C with a newly proposed method. Two gas-diffusion electrodes, consisting of Pt catalysts supported on carbon black and Nafion® ionomer, were mounted in a fuel cell housing with and without Nafion® membrane. Mixed gas of H2 and air with a constant composition was supplied to the cell, simulating crossover to an anode or a cathode. The F− emission rates increased with increasing the relative humidity in both H2-rich and O2-rich conditions, probably due to the enhanced penetration of H2O2, and/or the relating radical in swollen electrolyte. It was found that an appreciable fraction of H2O2 or OH radical was easily scavenged at Pt particles in the catalyst layer or in the Pt-dispersed Nafion®, resulting in the suppressed F− emission rates. Degradation mechanism of PFSA electrolytes was discussed. Keywords: PEFC, Electrolyte degradation, Nafion, Pt particle, Decomposition rat

  • synthesis and properties of novel sulfonated polyimides containing 1 5 naphthylene moieties
    Journal of Polymer Science Part A, 2003
    Co-Authors: Kenji Miyatake, Naoki Asano, Masahiro Watanabe
    Abstract:

    A series of novel sulfonated polyimides (equivalent weight per sulfonic Acid = 310–744 g/equiv) containing 10–70 mol % 1,5-naphthylene moieties were synthesized as potential electrolyte materials for high-temperature polymer electrolyte fuel cells. The polycondensation of 1,4,5,8-naphthalene tetracarboxylic dianhydride, 4,4′-diamino-2,2′-biphenyldisulfonic Acid, and 1,5-diaminonaphthalene gave the title polymer electrolytes. The polyimide electrolytes were high-molecular-weight (number-average molecular weight = 36.0–350.7 × 103 and weight-average molecular weight = 70.4–598.5 × 103) and formed flexible and tough films. The thermal properties (decomposition temperature > 260 °C, no glass-transition temperature), stability to oxidation, and water absorption were analyzed and compared with those of Perfluorosulfonic Acid polymers. The polyimide containing 20 mol % 1,5-naphthylene moieties showed higher proton conductivity (0.3 S cm−1) at 120 °C and 100% relative humidity than Perfluorosulfonic Acid polymers. The temperature and humidity dependence of the proton conductivity was examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3901–3907, 2003

Jiujun Zhang - One of the best experts on this subject based on the ideXlab platform.

  • a review of accelerated stress tests of mea durability in pem fuel cells
    International Journal of Hydrogen Energy, 2009
    Co-Authors: Haijiang Wang, Shengsheng Zhang, Xiaozi Yuan, Walter Merida, Hong Zhu, Jun Shen, Jiujun Zhang
    Abstract:

    Abstract This paper is a review of recent work done on accelerated stress tests in the study of PEM fuel cell durability, with a primary focus on the main components of the membrane electrode assembly (MEA). The accelerated stressors for each component under different conditions are outlined, in an attempt to gain a detailed understanding of cell degradation with respect to microstructural change and performance attenuation in the Perfluorosulfonic Acid membrane, catalyst, and gas diffusion layers. Various techniques for evaluating the components' performance are presented, along with representative mitigation strategies. In addition, different degradation mechanisms proposed in recent publications are briefly reviewed.

  • A review of polymer electrolyte membranes for direct methanol fuel cells
    Journal of Power Sources, 2007
    Co-Authors: Vladimir Neburchilov, Jonathan J Martin, Haijiang Wang, Jiujun Zhang
    Abstract:

    This review describes the polymer electrolyte membranes (PEM) that are both under development and commercialized for direct methanol fuel cells (DMFC). Unlike the membranes for hydrogen fuelled PEM fuel cells, among which Perfluorosulfonic Acid based membranes show complete domination, the membranes for DMFC have numerous variations, each has its advantages and disadvantages. No single membrane is emerging as absolutely superior to others. This review outlines the prospects of the currently known membranes for DMFC. The membranes are evaluated according to various properties, including: methanol crossover, proton conductivity, durability, thermal stability and maximum power density. Hydrocarbon and composite fluorinated membranes currently show the most potential for low cost membranes with low methanol permeability and high durability. Some of these membranes are already beginning to impact the portable fuel cell market.

Xiaoming Ren - One of the best experts on this subject based on the ideXlab platform.

  • high performance direct methanol polymer electrolyte fuel cells
    Journal of The Electrochemical Society, 1996
    Co-Authors: Xiaoming Ren, Mahlon S Wilson, Shimshon Gottesfeld
    Abstract:

    Direct methanol fuel cells (DMFCs) using Pt‐Ru electrocatalysts and Perfluorosulfonic Acid membranes provide high performances if operated above 100°C with optimized catalyst layers. A decal transfer method is used to apply thin‐film catalyst/ionomer composite layers to Nation® membranes. A Nation 112 membrane/electrode assembly operating on 5 atm oxygen at 130°C yields a current of 670 mA/cm2 at 0.5 V cell voltage. Peak power density is 400 mW/cm2. The same cell operating on 3 atm air at 110°C yields 370 mA/cm2 at 0.5 V and provides a maximum power density of 250 mW/cm2.

  • high performance direct methanol polymer electrolyte fuel cells
    Journal of The Electrochemical Society, 1996
    Co-Authors: Xiaoming Ren, Mahlon S Wilson, Shimshon Gottesfeld
    Abstract:

    Direct methanol fuel cells (DMFCs) using Pt-Ru electrocatalysts and Perfluorosulfonic Acid membranes provide high performances if operated above 100 C with optimized catalyst layers. A decal transfer method is used to apply thin-film catalyst/ionomer composite layers to Nafion{reg_sign} membranes. A Nafion 112 membrane/electrode assembly operating on 5 atm oxygen at 130 C yields a current of 670 mA/cm{sup 2} at 0.5 V cell voltage. Peak power density is 400 mW/cm{sup 2}. The same cell operating on 3 atm air at 110 C yields 370 mA/cm{sup 2} at 0.5 V and provides a maximum power density of 250 mW/cm{sup 2}.

Yongming Zhang - One of the best experts on this subject based on the ideXlab platform.