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Showing papers on "Nafion published in 1992"


Journal ArticleDOI
TL;DR: In this paper, a study of the temperature dependence of the oxygen reduction kinetics at the Pt/Nafion interface is presented, and the results showed a linear increase of the Tafel slope with temperature in the low current density region.
Abstract: Results of a study of the temperature dependence of the oxygen reduction kinetics at the Pt/Nafion interface are presented. This study was carried out in the temperature range of 30-80 C and at 5 atm of oxygen pressure. The results showed a linear increase of the Tafel slope with temperature in the low current density region, but the Tafel slope was found to be independent of temperature in the high current density region. The values of the activation energy for oxygen reduction at the platinum/Nafion interface are nearly the same as those obtained at the platinum/trifluoromethane sulfonic acid interface but less than values obtained at the Pt/H3PO4 and Pt/HClO4 interfaces. The diffusion coefficient of oxygen in Nafion increases with temperature while its solubility decreases with temperature. These temperatures also depend on the water content of the membrane.

635 citations


Journal ArticleDOI
TL;DR: In this paper, the authors report on polymer electrolyte membranes that are catalyzed by the direct application of thin film catalyst layers cast from solutions of suspended Pt/C catalyst and solubilized Nafion ionomer.
Abstract: This paper reports on polymer electrolyte membranes that are catalyzed by the direct application of thin film catalyst layers cast from solutions of suspended Pt/C catalyst and solubilized Nafion ionomer. Both the ionomeric membrane and the solubilized ionmer are in the Na{sup +} form during casting to enable higher curing temperatures, which results in more robust catalyst layers. In addition to simplifying the fabrication process, the direct application apparently provides enhanced bonding at the interface between the membrane and the catalyst layer. Consequently, the performances of fuel cells utilizing these catalyzed membranes with ultra-low platinum loading are superior to those achieved with other approaches to polymer electrolyte membranes of low Pt loading.

466 citations


Journal ArticleDOI
TL;DR: In this article, a smart material made from a metallized ionomer membrane called Nafion has been developed to sense mechanical vibrations and generate a voltage response with a unique vibrational damping property.
Abstract: Vibration control has been achieved using state-of-the-art 'smart' materials. A 'smart' material has been developed from a metallized ionomer membrane called Nafion. This electroded material can sense mechanical vibrations and generate a voltage response. Electroded Nafion has a unique vibrational damping property. Damping with this material is achieved by dissipating the electrical energy generated as heat. This can be done using an external resistance or optimally by creating an internal conductive path. A prototype accelerometer cell has been developed which shows excellent linear characteristics and high sensitivity. It is found that the most critical element in both of the applications is the sum of the internal and the contact resistances of the electroded Nafion hydrogen pressure cell. Accordingly, a study of the resistance of these Nafion-based cells has been made and the results are included and discussed.

281 citations


Journal ArticleDOI
TL;DR: The development of a detection method based on the electrogenerated chemiluminescence of tris(2,2'-bipyridine)ruthenium(II), (Ru(bpy)3(2+], immobilized in a Nafion film coated on an electrode is discussed.
Abstract: The development of a detection method based on the electrogenerated chemiluminescence of tris(2,2'-bipyridine)ruthenium(II), (Ru(bpy)3(2+], immobilized in a Nafion film coated on an electrode is discussed. Control of the electrode potential controls creation of the reactive reagent Ru(bpy)3(3+) which reacts with certain analytes to yield chemiluminescence emission of intensity proportional to the analyte concentration. The reaction results in Ru(bpy)3(3+) being converted to Ru(bpy)3(2+), which then is recycled to Ru(bpy)3(3+) again at the electrode. This sensor has been used in flow injection to determine oxalate, alkylamines, and NADH. Detection limits are 1 microM, 10 nM, and 1 microM, respectively, with working ranges extending over 4 decades in concentration. Sensitivity is constant over the wide pH range from 3 to 10. With oxalate, and to a small extent with amines, emission intensities increase with increasing ionic strength; this was shown to be a phenomenon related to the Nafion film and not to the chemiluminescence reaction. Emission intensities increase with temperature. The sensor remains stable for several days with suitable storage conditions. Significant amounts of Ru(bpy)3(3+) are shown to be capable of storage within the film.

274 citations


Journal ArticleDOI
TL;DR: In this paper, the relationship between the transference number, the transport number, and the electro-osmotic drag coefficient is presented, and their relevance to water management is solid polymer-electrolyte fuel cells is discussed.
Abstract: The transport number of water in Nafion 117 membrane over a wide range of water contents is determined experimentally using a concentration cell. The transport number of water, the ratio f[sup m][sub o]/Z[sub o], is about 1.4 for a membrane equilibrated with saturated water vapor at 25[degrees]C, decreases slowly as the membrane is dehydrated, and falls sharply toward zero as the concentration of water approaches zero. In this paper, the relationship between the transference number, the transport number, and the electro-osmotic drag coefficient is presented, and their relevance to water management is solid-polymer-electrolyte fuel cells is discussed. Results are compared with other data available in the literature and with the theoretical maximum.

258 citations


Journal ArticleDOI
TL;DR: In this article, the dependence of the oxygen reduction kinetics on oxygen pressure was investigated in Proton Exchange Membrane (PEM) fuel cells, and the authors showed that the diffusion coefficient of oxygen is invariant with pressure, however, the diffusion coefficients for oxygen is lower when air is used as the equilibrating gas as compared to when oxygen is used for equilibration.
Abstract: The investigation of oxygen reduction kinetics at the platinum/Nafion interface is of great importance in the advancement of proton-exchange-membrane (PEM) fuel-cell technology. This study focuses on the dependence of the oxygen reduction kinetics on oxygen pressure. Conventional Tafel analysis of the data shows that the reaction order with respect to oxygen is unity at both high and low current densities. Chronoamperometric measurements of the transport parameters for oxygen in Nafion show that oxygen dissolution follows Henry's isotherm. The diffusion coefficient of oxygen is invariant with pressure; however, the diffusion coefficient for oxygen is lower when air is used as the equilibrating gas as compared to when oxygen is used for equilibration. These results are of value in understanding the influence of O2 partial pressure on the performance of PEM fuel cells and also in elucidating the mechanism of oxygen reduction at the platinum/Nafion interface.

215 citations


Journal ArticleDOI
TL;DR: In this article, the authors used electrochemical impedance spectroscopy (EIS) to study the oxygen-reduction reaction under lower humidification conditions than previously studied, and the results showed that the production of water due to electrochemical reduction of oxygen greatly influenced the EIS response and electrode kinetics at the Pt/Nafion interface.
Abstract: The objectives of this study were to use electrochemical impedance spectroscopy (EIS) to study the oxygen-reduction reaction under lower humidification conditions than previously studied. The EIS technique permits the discrimination of electrode kinetics of oxygen reduction, mass transport of O2 in the membrane, and the electrical characteristics of the membrane. Electrode-kinetic parameters for the oxygen-reduction reaction, corrosion current densities for Pt, and double-layer capacitances were calculated. The production of water due to electrochemical reduction of oxygen greatly influenced the EIS response and the electrode kinetics at the Pt/Nafion interface. From the finite-length Warburg behavior, a measure of the diffusion coefficient of oxygen in Nafion and diffusion-layer thickness was obtained. An analysis of the EIS data in the high-frequency domain yielded membrane and interfacial characteristics such as ionic conductivity of the membrane, membrane grain-boundary capacitance and resistance, and uncompensated resistance.

173 citations


Journal ArticleDOI
TL;DR: In this paper, three chemical techniques to platinize the surface of a Nafion polymer electrolyte membrane (PEM) to form a Pt/PEM electrode have been studied.
Abstract: Three chemical techniques to platinize the surface of a Nafion polymer electrolyte membrane (PEM) to form a Pt/PEM electrode have been studied. The resulting Pt/PEM composites were characterized visually by transmission electron microscopy and scanning electron microscopy and electrochemically by (i) hydrogen adsorption to determine surface area, and (ii) the polarization characteristics for the oxidation of hydrogen. The Takenaka‐Torikai method was used in which a reductant diffuses through the membrane to contact and reduce platinic acid at the opposite face, and two variations of an impregnation‐reduction procedure were employed in which a cationic salt is first impregnated into the Nafion and subsequently the membrane is exposed to a reductant. A previously reported equilibrium impregnation method was modified such that the impregnation step was not carried to equilibrium and the concentration of the anionic reductant was significantly lowered. Upon judicious choice of the fabrication conditions, platinum deposited by the nonequilibrium impregnation ‐reduction procedure is concentrated in a thin (submicron), porous layer located predominantly within the membrane but near the surface where it is accessible to both gaseous reactants and a current collector. The metal distribution forms an electrode with a larger active surface area per unit weight of platinum and a better platinum utilization (mA/mg Pt for the hydrogen oxidation reaction) compared to Pt/PEM electrode prepared by the equilibrium impregnation‐reduction process or the Takenaka‐Torikai method. The chemical and physical processes which occur to affect the metal film formed in all three techniques are discussed.

130 citations


Journal ArticleDOI
TL;DR: In this paper, the location of Nafion R in solid polymer-electrolyte-fuel-cell electrodes was investigated by porosimetry and scanning microprobe analysis.
Abstract: The location of Nafion R in solid-polymer-electrolyte-fuel-cell electrodes was investigated by porosimetry and scanning microprobe analysis. At low Nafion loadings, the polymeric electrolyte uniformly fills the micro- and macropores of the electrode structure and increases its ionic conductivity. The pores are completely filled in the range from 0.8 to 1.0 mg of Nafio/cm 2 of electrode, and further addition of polymer results in the formation of a film on the external surface of the electrode. This film causes an additional resistance in series with the ionic resistance in the active layer

124 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of casting solvent choice and thermal curing on the permeability and diffusion coefficients of substrates in the perfluorinated sulfonic acid ionomer, Nafion, has been examined for the neutral species glucose [pH 13], hydroquinone (QH 2 )[pH 7.4], and ascorbic acid (pH 1.3]
Abstract: The effect of casting solvent choice and thermal curing on the permeability and diffusion coefficients of substrates in the perfluorinated sulfonic acid ionomer, Nafion, has been examined for the neutral species glucose [pH 13], hydroquinone (QH 2 )[pH 7.4], and ascorbic acid [pH 1.3], as well as the cation [(trimethylammonio)methyl]ferrocene (FcTMA + )[pH 7]

115 citations


Journal ArticleDOI
TL;DR: In this paper, a minicell based on a filmed microelectrode was used to study the oxygen reduction kinetics at the Pt/recast Nafion interface.
Abstract: We describe a study of the oxygen reduction kinetics at the Pt/recast Nafion ® interface employing a minicell based on a filmed microelectrode. The experimental conditions are identical to those in polymer-electrolyte fuel cells in that the recast ionomer electrolyte is exposed only to water vapor. We find that the interfacial rate of oxygen reduction near 0.9 V is similar for the Pr/recast ionomer interface and for Pt immersed in dilute aqueous acid solutions. A significant loss of oxygen reduction activity occurs when the recast ionomer electrolyte loses water. We discuss a possible evaluation of catalyst utilization in polymer electrolyte fuel cells

Journal ArticleDOI
TL;DR: In this article, the electrode kinetics of oxygen reduction at the platinum microcrystallite/Nafion® interface were investigated as a function of temperature and pressure, and the effects of platinum loading and Nafion impregnation on the electrode kinetic parameters were elucidated.


Journal ArticleDOI
TL;DR: In this article, a novel glucose biosensor was prepared by deposition of a mixture containing glucose oxidase dissolved in water and Nafion dissolved in methanol at the surface of a platinum disk electrode.
Abstract: A novel glucose biosensor has been prepared by deposition of a mixture containing glucose oxidase dissolved in water and Nafion dissolved in methanol at the surface of a platinum disk electrode. Glucose concentration is evaiuated by measuring the amperometric current corresponding to hydrogen peroxide electrooxidation at 0.7 V vs. SCE. The addition of glucose oxidase to Nafion resulted in a Nafion-glucose oxidase film that was more permeable to anionic species than Nafion alone. The calibration curve for glucose is linear from 5 μM up to about 10 mM. In oxygen-saturated solution, the linear range extended to 15 mM. The optimum pH for the assay was found to be 5.5. The enzyme is not stabilized against temperature deactivation when it is immobilized in Nafion. The Pt/Nafion-glucose oxidase electrodes showed good stability when stored dry at room temperature with 80% of the initial response retained after 250 days.

Journal ArticleDOI
TL;DR: The phase transition behavior of water in the perfluorosulfonate ionomer membrane, Nafion, was investigated using a differential scanning calorimeter (DSC).

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the charge and discharge characteristics of polyaniline (PAn)-Nafion®-PAn composite films used as rechargeable batteries and found that cells with LiClO4 in propylene carbonate as electrolyte showed the highest capacity.
Abstract: The charge-discharge characteristics of polyaniline (PAn)-Nafion®-PAn composite films used as rechargeable batteries were investigated. The batteries were formed chemically by sandwiching Nafion® between two thin layers of PAn-Nafion® composite in equilibrium with various electrolytes. It was found that cells with LiClO4 in propylene carbonate as electrolyte showed the highest capacity. The charge and discharge performance of the battery was almost independent of the choice of anions but was significantly affected by cation size. This may indicate that the insertion or removal of charge-compensating electrolyte cations from the composite layer was responsible for the redox of PAn during the charge and discharge cycles.

Journal ArticleDOI
TL;DR: The FT-IR spectra of Nafion 117, Raipore 1010, and PESS membranes loaded with different alkaline counterions and equilibrated with different liquid media were recorded by means of the attenuated total reflectance technique as mentioned in this paper.
Abstract: SYNOPSIS FT-IR spectra of Nafion 117, Raipore 1010, and PESS membranes loaded with different alkaline counterions and equilibrated with different liquid media were recorded by means of the attenuated total reflectance technique. The antisymmetric ( va) and especially the symmetric stretching vibrations ( vs) of the sulfonate groups are affected by the presence of solvents in its local chemical environment. In the dry membrane the smaller the bare counterion, the higher the frequency of the symmetric vibration and the stronger the sulfonate-counterion interactions in the contacting ion pair. After equilibration with pure water, ethanol, and 2-propanol, the v, vibration shifts to a constant value corresponding to the solvated sulfonic grouping in the case of Nafion-Li’ membrane. In the cases of PESS-Li+ and Raipore-Li+ membrane only water can cause a similar shift. The greater affinity of the Nafion membrane to alcohols can be attributed to the stronger acidity of the corresponding sulfonic acid. In water-alcohol mixtures the variation of v, with water content indicates that the ion pairs in the PESS-Li+ membrane are progressively dissociated and solvated by increasing amounts of water in 2-propanol. Complete dissociation occurs at about 9 wt % water. Smaller shifts are observed with bigger cations, due to the weaker sulfonate-cation interactions.

ReportDOI
01 Jul 1992
TL;DR: In this article, a transport model for polymer electrolytes is presented, based on concentrated solution theory and irreversible thermodynamics, and the relation between transference number, transport number, and electroosmotic drag coefficient is discussed.
Abstract: A transport model for polymer electrolytes is presented, based on concentrated solution theory and irreversible thermodynamics. Thermodynamic driving forces are developed, transport properties are identified and experiments devised. Transport number of water in Nafion 117 membrane is determined using a concentration cell. It is 1.4 for a membrane equilibrated with saturated water vapor at 25{degrees}C, decreases slowly as the membrane is dehydrated, and falls sharply toward zero as the water content approaches zero. The relation between transference number, transport number, and electroosmotic drag coefficient is presented, and their relevance to water-management is discussed. A mathematical model of transport in a solid-polymer-electrolyte fuel cell is presented. A two-dimensional membrane-electrode assembly is considered. Water management, thermal management, and utilization of fuel are examined in detail. The membrane separators of these fuel cells require sorbed water to maintain conductivity; therefore it is necessary to manage the water content in membranes to ensure efficient operation. Water and thermal management are interrelated. Rate of heat removal is shown to be a critical parameter in the operation of these fuel cells. Current-voltage curves are presented for operation on air and reformed methanol. Equations for convective diffusion to a rotating disk are solved numerically for a consolutemore » point between the bulk concentration and the surface. A singular-perturbation expansion is presented for the condition where the bulk concentration is nearly equal to the consolute-point composition. Results are compared to Levich's solution and analysis.« less

Journal ArticleDOI
TL;DR: In this paper, the authors used microtip electrodes positioned just above Nafion-coated electrodes to monitor the ejection of countercatlons from polyelectrolyte polynafion coatings.
Abstract: The ideal cation permselectivity exhibited by electrode coatings prepared from the polyelectrolyte Nafion leads to ejection of countercatlons from the coatings during electrochemical oxidation of Os(bpy)_3^(2+) counterions incorporated in the coatings. If the coatings are saturated with Os(bpy)_3^(2+) so that these are the only counterions present, one-third of the incorporated cations are ejected during the oxidation of Os(bpy)_3^(2+) to Os(bpy)_3^(3+). The cyclic voltammetry of the incorporated Os(bpy)_3^(3+/2+) couple is altered substantially in the absence of additional counterions. The changes are attributed to contributions to the voltammetric potentials from the free energy of transfer of these strongly bound counterions. Microtip electrodes positioned just above Nafion-coated electrodes were used to monitor the ejection of both Os(bpy)_3^(3+) and Os(bpy)_3^(2+) from Nafion coatings. Much more of the former complex lo ejected from saturated coatings which is believed to be the result of electric field-assisted ejection.

Journal ArticleDOI
TL;DR: In this article, the results of a study on the electro-oxidation of methanol vapor at a platinized polymer electrolyte membrane (PEM) were reported, and the PEM was Nafion 117 and served both as a medium for proton transport and a barrier separating anodic from cathodic products.
Abstract: The results of a study on the electro-oxidation of methanol vapor at a platinized polymer electrolyte membrane (PEM) are reported. The PEM was Nafion 117 and serves both as a medium for proton transport and a barrier separating anodic from cathodic products. The counterelectrode was immersed in an aqueous acid solution with which the unmetallized face of the PEM was in contact

Journal ArticleDOI
TL;DR: In this paper, analytical electron microscopy was used to study the ion exchange membrane Nafion 117, a product of the Du Pont Company showing high ionic conductivity and good mechanical properties.

Journal ArticleDOI
TL;DR: In this article, a commercially available Nafion drier (Perma-Pure) was tested under laboratory and field conditions and shown to be suitable for measurements of reduced sulfur compounds such as H2S, COS, CH3SH, DMS and CS2 in dry and humid air in the pptv-range.

Journal ArticleDOI
TL;DR: In this paper, the pore models for the equilibrium electrolyte absorption in ion exchange membranes are compared to experimental results from the literature for Nafion 120 and Naphion 117 membranes as well as to new experimental results for a Permion radiation-grafted membrane.

Journal ArticleDOI
01 Jan 1992-Analyst
TL;DR: In this paper, a theoretical model describing heterogeneous redox catalysis at metal oxide-Nafion composite modified electrodes is presented, where metal oxide particles are assumed to be dispersed in a homogeneous manner within the polymeric Nafion matrix.
Abstract: A theoretical model describing heterogeneous redox catalysis at metal oxide–Nafion composite modified electrodes is presented. The metal oxide particles are assumed to be dispersed in a homogeneous manner within the polymeric Nafion matrix. The composite material is deposited on the surface of a support electrode in the form of a thin film. The surface of each oxide particle is assumed to be catalytically active. The interaction between substrate and the catalytically active oxymetal surface group is assumed to follow Michaelis–Menten kinetics. The transport and kinetics of the substrate within the polymer film is examined and various limiting expressions for the reaction flux are proposed. The theoretical predictions are compared with experimental results obtained for the electro-oxidation of catechol at RuO2–Nafion composite electrodes.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the photostability of laser dye rhodamine 6G in perfluorosulphonate cation-exchange membrane (Nafion) from aqueous solution.
Abstract: Sorption of laser dye rhodamine 6G in perfluorosulphonate cation-exchange membrane (Nafion) from aqueous solution has been investigated by optical absorption and emission studies. In the H+ form, the optical absorption spectra changes with water content in the membrane and is attributed to the change in H+ ion concentration in dry and wet (with water) conditions of the membrane. The dye is present in the protonated form in the dry membrane and in the cationic form in the wet membrane. In the Na+ form, rhodamine 6G is present in the cationic form and the optical absorption spectra do not show changes in dry and water-wet conditions of the membrane. The fluorescence lifetime of rhodamine 6G is 3.97 ns and decay is single exponential. In the Na+ and H+ forms of the membrane, the fluorescence decay is biexponential. The lifetime and the relative ratio vary for the Na+ and H+ forms and also with the water content in the membrane. Owing to the large size of the dye low values for the diffusion coefficient are observed (3.2 × 10–11 and 2.0 × 10–8 cm2 s–1 for Na+ and H+ form of Nafion, respectively). As compared to aqueous solutions, rhodamine 6G in Nafion membrane is observed to be photostable.

Journal ArticleDOI
TL;DR: By using composite films of hydrolyzed Nafion and dyes having a terminal N-phenyl group, an optical humidity sensor has been fabricated as discussed by the authors, where the optical intensity of the absorption peaks which depend on the dyes used was influenced by relative humidity.
Abstract: By using composite films of hydrolyzed Nafion and dyes having a terminal N-phenyl group, an optical humidity sensor has been fabricated. In the reflection mode, the optical intensity of the absorption peaks which depend on the dyes used was influenced by relative humidity. In dry air, the alkyl amine group reacted with SO 3 H of hydrolyzed Nafion and formed a proton additive. Sorption of water molecules induces the deprotonation of the quaternized ammonium group.

Journal ArticleDOI
TL;DR: In this article, the electrochemical behavior of UO 2 2+ solutions at Nafion ® -coated glassy carbon electrodes has been examined and compared with the behaviour observed at uncoated electrodes.


Journal ArticleDOI
TL;DR: In this article, a short side chain perfluorosulfonate ionomer membrane films, made by Dow Chemical Company, have been measured as a function of equivalent weight of the polymer.

Journal ArticleDOI
TL;DR: In this paper, Geraniol was electrochemically oxidized to citral by a Solid Polymer Electrolyte (SPE) method, using manganese-modified platinum-Nafion electrodes.