The Experts below are selected from a list of 6306 Experts worldwide ranked by ideXlab platform
Steven Holdcroft - One of the best experts on this subject based on the ideXlab platform.
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electrochemical reduction of dissolved Oxygen in alkaline solid polymer electrolyte films
Journal of the American Chemical Society, 2016Co-Authors: David Novitski, Aslan Kosakian, Thomas Weissbach, Marc Secanell, Steven HoldcroftAbstract:Mass transport of Oxygen through an ionomer contained within the cathode catalyst layer in an anion exchange membrane fuel cell is critical for a functioning fuel cell, yet is relatively unexplored. Moreover, because water is a reactant in the Oxygen reduction reaction (ORR) in alkaline media, an adequate supply of water is required. In this work, ORR mass transport behavior is reported for methylated hexamethyl-p-terphenyl polymethylbenzimidazoles (HMT-PMBI), charge balanced by hydroxide ions (IEC from 2.1 to 2.5 mequiv/g), and commercial Fumatec FAA-3 membranes. Electrochemical mass transport parameters are determined by potential step chronoamperometry using a Pt microdisk solid-state electrochemical cell, in air at 60 °C, with relative humidity controlled between 70% and 98%. The Oxygen Diffusion Coefficient (DbO2), Oxygen concentration (cbO2), and Oxygen permeability (DbO2·cbO2) were obtained by nonlinear curve fitting of the current transients using the Shoup–Szabo equation. Mass transport parameter...
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effect of equivalent weight on electrochemical mass transport properties of Oxygen in proton exchange membranes based on sulfonated α β β trifluorostyrene bam and sulfonated styrene ethylene butylene styrene triblock dais analytical copolymers
Journal of Electroanalytical Chemistry, 2001Co-Authors: Vesna I Basura, Paul D Beattie, Carmen Chuy, Steven HoldcroftAbstract:Abstract Mass transport parameters and limiting current densities are determined for a series of sulfonated α,β,β-trifluorostyrene-co-substituted-α,β,β-trifluorostyrene (BAM®) (EW 407-735 g mol−1) and sulfonated styrene-(ethylene-butylene)-styrene copolymers (DAIS-Analytical) (EW 585–1062 g mol−1) proton exchange membranes using microelectrode techniques. These materials were investigated in an environment that mimics proton exchange membrane fuel cells. The Oxygen Diffusion Coefficient increases with temperature, while its solubility decreases. All membranes exhibit a Henry's Law dependence for the limiting current of the Oxygen reduction reaction with increasing Oxygen pressure. The limiting current and the Oxygen Diffusion Coefficient decreases with increasing equivalent weight, while the solubility of Oxygen decreases due to the corresponding change in water content. These data are discussed in the context of previously published data on Nafion 117 and ethylenetetrafluoroethylene-g-polystyrene sulfonic acid membranes.
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electrochemical characterization of ethylenetetrafluoroethylene g polystyrenesulfonic acid solid polymer electrolytes
Journal of The Electrochemical Society, 2000Co-Authors: Carmen Chuy, Vesna I Basura, Steven Holdcroft, Evelyne Simon, J A Horsfall, Keith V LovellAbstract:Electrochemical characterization of a series of membranes based on polystyrenesulfonic acid grafted onto ethylenetetrafluoroethylene (ETFE-g-PSSA) was determined by chronoamperometry with a microdisk electrode using a solid‐state electrochemical cell at 100% relative humidity and over a range of temperatures. The Oxygen Diffusion Coefficient and permeability increased with decreasing equivalent weight (EW). Oxygen solubility marginally decreased. These observations can be explained on the basis of increasing water content with decreasing EW. Proton conductivity also increased with water content and does not directly correlate with proton concentration within the membrane. © 2000 The Electrochemical Society. All rights reserved.
Motoaki Kawase - One of the best experts on this subject based on the ideXlab platform.
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theoretical examination of effective Oxygen Diffusion Coefficient and electrical conductivity of polymer electrolyte fuel cell porous components
Journal of Power Sources, 2016Co-Authors: Gen Inoue, Kouji Yokoyama, Junpei Ooyama, Takeshi Terao, Tomomi Tokunaga, Norio Kubo, Motoaki KawaseAbstract:Abstract The reduction of Oxygen transfer resistance through porous components consisting of a gas Diffusion layer (GDL), microporous layer (MPL), and catalyst layer (CL) is very important to reduce the cost and improve the performance of a PEFC system. This study involves a systematic examination of the relationship between the Oxygen transfer resistance of the actual porous components and their three-dimensional structure by direct measurement with FIB-SEM and X-ray CT. Numerical simulations were carried out to model the properties of Oxygen transport. Moreover, based on the model structure and theoretical equations, an approach to the design of new structures is proposed. In the case of the GDL, the binder was found to obstruct gas Diffusion with a negative effect on performance. The relative Diffusion Coefficient of the MPL is almost equal to that of the model structure of particle packing. However, that of CL is an order of magnitude less than those of the other two components. Furthermore, an equation expressing the relative Diffusion Coefficient of each component can be obtained with the function of porosity. The electrical conductivity of MPL, which is lower than that of the carbon black packing, is considered to depend on the contact resistance.
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effect of porous structure of catalyst layer on effective Oxygen Diffusion Coefficient in polymer electrolyte fuel cell
Journal of Power Sources, 2016Co-Authors: Gen Inoue, Motoaki KawaseAbstract:Abstract It is important to reduce the Oxygen Diffusion resistance through PEFC porous electrode, because it is the key to reduce the PEFC cost. However, the gas Diffusion Coefficient of CL is lower than MPL in spite of framework consisted of same carbon blacks. In this study, in order to understand the reasons of the lower gas Diffusion performance of CL, the relationship between a carbon black agglomerate structure and ionomer adhesion condition is evaluated by a numerical analysis with an actual reconstructed structure and a simulated structure. As a result, the gas Diffusion property of CL strongly depends on the ionomer adhesion shape. In the case of adhesion shape with the same curvature of ionomer interface, each pore can not be connected enough. So the pore tortuosity increases. Moreover, in the case of existence of inefficient large pores formed by carbon black agglomerate and ununiformly coated ionomer, the gas Diffusion performance decrease rapidly. As the measurement values in actual CL are almost equal to that with model structure with inefficient large pores. These characteristics can be confirmed by actual cross-section image obtained by FIB-SEM.
J P Loup - One of the best experts on this subject based on the ideXlab platform.
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chemical Oxygen Diffusion Coefficient measurement by conductivity relaxation correlation between tracer Diffusion Coefficient and chemical Diffusion Coefficient
Journal of The European Ceramic Society, 2004Co-Authors: Fabrice Mauvy, Jean-marc. Bassat, Emmanuelle Boehm, P Dordor, J C Grenier, J P LoupAbstract:Abstract Chemical Oxygen Diffusion Coefficient ( D ) was measured by conductivity relaxation experiments on La2Cu0.5Ni0.5O4+δ ceramics. This method consists of abruptly changing the Oxygen partial pressure in the surrounding atmosphere of the sample. The consequent evolution of the electrical conductivity is recorded as a function of time, at fixed temperature. The transient behaviour during the re-equilibration process is analysed on the basis of the second Fick's law. In parallel, the Oxygen tracer self-Diffusion Coefficient (D*) was derived from isotopic exchange experiments monitored by SIMS analysis. Finally, the Oxygen over-stoichiometry (δ) was computed from thermogravimetric experiments, under different pO2, in order to determined the thermodynamic factor (γ). A quantitative agreement between D and γ×D*, observed over a wide temperature range (500–900 °C), confirms the validity of the experimental method and of the Wagner's theory, applied to the Oxygen Diffusion in this compound.
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measurement of chemical and tracer Diffusion Coefficients of Oxygen in la2cu0 5ni0 5o4 δ
Solid State Ionics, 2003Co-Authors: Fabrice Mauvy, Jean-marc. Bassat, Emmanuelle Boehm, P Dordor, J P LoupAbstract:Abstract In mixed electronic and ionic conductors O 2− /e − (MIEC), where the electronic conductivity is dominant, the determination of the Oxygen Diffusion Coefficient is an essential feature. In the present paper, the Oxygen chemical Diffusion Coefficient D O of a MIEC oxide has been evaluated using the conductivity relaxation method, in the temperature range 773–1173 K. Samples of La 2 Cu 0.5 Ni 0.5 O 4+ δ were selected because of the high value of their surface exchange Coefficient. In addition, the Oxygen Diffusion Coefficient D * was determined from the 18 O tracer Diffusion profile. Finally, the Oxygen partial pressure dependence of this compound was determined by thermogravimetric analysis (TGA). On the basis of these three independent experiments, the model of ambipolar Diffusion, which describes the Diffusion in mixed oxide, has been experimentally verified. For such a determination of the intrinsic Diffusion characteristics, dense samples are required.
Jean-marc. Bassat - One of the best experts on this subject based on the ideXlab platform.
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chemical Oxygen Diffusion Coefficient measurement by conductivity relaxation correlation between tracer Diffusion Coefficient and chemical Diffusion Coefficient
Journal of The European Ceramic Society, 2004Co-Authors: Fabrice Mauvy, Jean-marc. Bassat, Emmanuelle Boehm, P Dordor, J C Grenier, J P LoupAbstract:Abstract Chemical Oxygen Diffusion Coefficient ( D ) was measured by conductivity relaxation experiments on La2Cu0.5Ni0.5O4+δ ceramics. This method consists of abruptly changing the Oxygen partial pressure in the surrounding atmosphere of the sample. The consequent evolution of the electrical conductivity is recorded as a function of time, at fixed temperature. The transient behaviour during the re-equilibration process is analysed on the basis of the second Fick's law. In parallel, the Oxygen tracer self-Diffusion Coefficient (D*) was derived from isotopic exchange experiments monitored by SIMS analysis. Finally, the Oxygen over-stoichiometry (δ) was computed from thermogravimetric experiments, under different pO2, in order to determined the thermodynamic factor (γ). A quantitative agreement between D and γ×D*, observed over a wide temperature range (500–900 °C), confirms the validity of the experimental method and of the Wagner's theory, applied to the Oxygen Diffusion in this compound.
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Oxygen Diffusion Coefficient and Oxygen exchange Coefficient of bimevox 10 me cu co ceramic membranes
Solid State Ionics, 2003Co-Authors: M Guillodo, Laurent Dessemond, Jean-marc. Bassat, Jacques Fouletier, P GalloAbstract:Abstract The 18 O/ 16 O Isotope Exchange Depth Profile technique (IEDP) was applied to BIMEVOX.10 (ME=Cu, Co) materials to determine their Oxygen exchange Coefficients and bulk Oxygen tracer Diffusion Coefficients. These results are compared to the exchange current densities obtained from current–voltage curves and bulk conductivity determined by impedance spectroscopy. These results confirm that, in spite of a noticeably higher ionic conductivity than that of the classical oxide electrolytes such as yttria stabilized zirconia (YSZ) or gadolinia-doped ceria (GDC), the Oxygen surface exchange Coefficients are low.
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measurement of chemical and tracer Diffusion Coefficients of Oxygen in la2cu0 5ni0 5o4 δ
Solid State Ionics, 2003Co-Authors: Fabrice Mauvy, Jean-marc. Bassat, Emmanuelle Boehm, P Dordor, J P LoupAbstract:Abstract In mixed electronic and ionic conductors O 2− /e − (MIEC), where the electronic conductivity is dominant, the determination of the Oxygen Diffusion Coefficient is an essential feature. In the present paper, the Oxygen chemical Diffusion Coefficient D O of a MIEC oxide has been evaluated using the conductivity relaxation method, in the temperature range 773–1173 K. Samples of La 2 Cu 0.5 Ni 0.5 O 4+ δ were selected because of the high value of their surface exchange Coefficient. In addition, the Oxygen Diffusion Coefficient D * was determined from the 18 O tracer Diffusion profile. Finally, the Oxygen partial pressure dependence of this compound was determined by thermogravimetric analysis (TGA). On the basis of these three independent experiments, the model of ambipolar Diffusion, which describes the Diffusion in mixed oxide, has been experimentally verified. For such a determination of the intrinsic Diffusion characteristics, dense samples are required.
Gen Inoue - One of the best experts on this subject based on the ideXlab platform.
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theoretical examination of effective Oxygen Diffusion Coefficient and electrical conductivity of polymer electrolyte fuel cell porous components
Journal of Power Sources, 2016Co-Authors: Gen Inoue, Kouji Yokoyama, Junpei Ooyama, Takeshi Terao, Tomomi Tokunaga, Norio Kubo, Motoaki KawaseAbstract:Abstract The reduction of Oxygen transfer resistance through porous components consisting of a gas Diffusion layer (GDL), microporous layer (MPL), and catalyst layer (CL) is very important to reduce the cost and improve the performance of a PEFC system. This study involves a systematic examination of the relationship between the Oxygen transfer resistance of the actual porous components and their three-dimensional structure by direct measurement with FIB-SEM and X-ray CT. Numerical simulations were carried out to model the properties of Oxygen transport. Moreover, based on the model structure and theoretical equations, an approach to the design of new structures is proposed. In the case of the GDL, the binder was found to obstruct gas Diffusion with a negative effect on performance. The relative Diffusion Coefficient of the MPL is almost equal to that of the model structure of particle packing. However, that of CL is an order of magnitude less than those of the other two components. Furthermore, an equation expressing the relative Diffusion Coefficient of each component can be obtained with the function of porosity. The electrical conductivity of MPL, which is lower than that of the carbon black packing, is considered to depend on the contact resistance.
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effect of porous structure of catalyst layer on effective Oxygen Diffusion Coefficient in polymer electrolyte fuel cell
Journal of Power Sources, 2016Co-Authors: Gen Inoue, Motoaki KawaseAbstract:Abstract It is important to reduce the Oxygen Diffusion resistance through PEFC porous electrode, because it is the key to reduce the PEFC cost. However, the gas Diffusion Coefficient of CL is lower than MPL in spite of framework consisted of same carbon blacks. In this study, in order to understand the reasons of the lower gas Diffusion performance of CL, the relationship between a carbon black agglomerate structure and ionomer adhesion condition is evaluated by a numerical analysis with an actual reconstructed structure and a simulated structure. As a result, the gas Diffusion property of CL strongly depends on the ionomer adhesion shape. In the case of adhesion shape with the same curvature of ionomer interface, each pore can not be connected enough. So the pore tortuosity increases. Moreover, in the case of existence of inefficient large pores formed by carbon black agglomerate and ununiformly coated ionomer, the gas Diffusion performance decrease rapidly. As the measurement values in actual CL are almost equal to that with model structure with inefficient large pores. These characteristics can be confirmed by actual cross-section image obtained by FIB-SEM.
