scispace - formally typeset
Search or ask a question

Showing papers on "Nafion published in 1993"


Journal ArticleDOI
TL;DR: In this article, the diffusion coefficient and relaxation time of water in the membrane and the protonic conductivity of the membrane as functions of membrane water content were measured, and the ratio of water molecules carried across the membrane per proton transported, the electro-osmotic drag coefficient, was determined for a limited number of water contents.
Abstract: Water uptake and transport properties of Nafion[reg sign] 117 membranes at 30 C are reported here. Specifically, the authors have determined the amount of water taken up by membranes immersed in liquid water and by membranes exposed to water vapor of variable water activity. Transport parameters measured are the diffusion coefficient and relaxation time of water in the membrane and the protonic conductivity of the membrane as functions of membrane water content. The ratio of water molecules carried across the membrane per proton transported, the electro-osmotic drag coefficient, also was determined for a limited number of membrane water contents. The drag coefficient is contrasted with the experimentally determined net water transport across an operating PEM fuel cell.

1,412 citations


Journal ArticleDOI
TL;DR: In this article, water uptake and transport parameters measured at 30 C for several available perfluorosulfonic acid membranes are compared and 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.
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.

648 citations


Journal ArticleDOI
TL;DR: In this article, the density and dimensional changes of Nafion 117 H have been measured as a function of the water content and some anisotropy of dimensional changes was observed.
Abstract: The density and dimensional changes of Nafion 117 H have been measured as a function of the water content. Swelling of Nafion commences at N (≡ mol ratio water to hydrogen ion) ∼ 1.9. Some anisotropy of dimensional changes was observed. Water-sorption isotherms obey Henry's Law with a nonzero intercept indicating some water retention. The diffusion coefficient of water in Nafion and the electrical conductivity of Nafion are strong functions of the water content. The latter is exploited for the development of a humidity sensor. © 1993 John Wiley & Sons, Inc.

347 citations


Journal ArticleDOI
TL;DR: In this paper, a two-and four-electrode geometry was used to distinguish between the membrane impedance and the interfacial impedances, and it was shown that the impedance of Nafion for frequencies up to 100 kHz is characterized by a pure resistance, similar to conventional liquid electrolytes.
Abstract: AC impedance spectroscopy has been employed to study the conduction of protons in Nafion 117 polymer electrolyte membranes. Both two- and four-electrode geometries have been used to uniquely distinguish between the membrane impedance and the interfacial impedances. The results show that the impedance of Nafion for frequencies up to 100 kHz is characterized by a pure resistance, similar to conventional liquid electrolytes. The frequency dependent features observed using a two-electrode geometry are shown to be consistent with well-characterized interfacial impedances and do not arise from ionic conduction in the membrane. These results show that previous two-electrode studies reported in the literature have misinterpreted the impedance of the electrode interfaces as belonging to the conduction process in the electrolyte.

140 citations


Journal ArticleDOI
TL;DR: In this paper, the authors compared the electrode kinetic parameters, electrochemically active surface areas, activation energies and reaction orders for the oxygen reduction reaction (ORR) in the sputtered and unsputtered electrodes in proton exchange membrane fuel cells as functions of temperature and pressure.

139 citations


Journal ArticleDOI
TL;DR: In this paper, the authors show a homogeneous distribution of polystyrene across the grafted film and show that the specific resistivity decreases with increasing degree of grafting, reflected by an increasing hydration of the sulfonic acid groups.

95 citations


Journal ArticleDOI
TL;DR: In this paper, Nafion tubes that function both as a reaction catalyst and a pervaporation membrane have been used to increase the yield in the esterification of acetic acid with methanol and n -butanol by selectively removing products, mainly water, from the reaction mixture.

78 citations


Journal ArticleDOI
TL;DR: Extended x-ray absorption fine structure (EXAFS) spectroscopy was used to investigate the precipitation of metallic platinum into Nafion ionomer membranes in this paper, where the four amine groups remain linked to the platinum atom even after dissolution and incorporation into the membrane.
Abstract: Extended x-ray absorption fine structure (EXAFS) spectroscopy was used to investigate the precipitation of metallic platinum into Nafion ionomer membranes. First, x-ray absorption spectra above the PtL III edge were obtained to compare the structure of platinum tetramine (i) solid, (ii) dissolved in water, and (iii) incorporated to Nafion sheets. The four amine groups remain linked to the platinum atom even after dissolution and incorporation into the membrane. EXAFS collected with dispersive optics was used to follow in situ the incorporation and the precipitation of the salt at PtL III edge. Time dependent concentrations of platinum salt in the membrane were obtained by measuring the time variation of the absorbance of the sample

69 citations


Journal ArticleDOI
TL;DR: In this paper, perovskite electrocatalysts demonstrating activity towards direct methanol oxidation during cyclic voltammetry measurements included, respectively,,,,,,, and where gave methenol oxidation currents up to 28 mA/cm2 at 0.45 V vs. SCE.
Abstract: This investigation explores direct methanol fuel cells incorporating perovskite anode electrocatalysts. Preliminary electrochemical performance was addressed following incorporation of electrocatalysts into polymer electrolyte (Nafion 417) fuel cells. Perovskite electrocatalysts demonstrating activity towards direct methanol oxidation during cyclic voltammetry measurements included, respectively, , , , , , ,, and where gave methanol oxidation currents up to 28 mA/cm2 at 0.45 V vs. SCE. Correlations were found between electrocatalyst solid‐state and thermodynamic parameters corresponding to, respectively, molecular electronic polarizability (α), the optical dielectric constant (∈), the perovskite spin‐only magnetic moment, the number of d‐electrons in perovskite A and B lattice sites , and the average metal‐oxygen binding energy for the perovskite lattice , and corresponding fuel cell performance. This may have future merit for the prediction of new electrocatalyst family members for promoting direct methanol oxidation. Methanol diffusion from anode to cathode compartments appears to be a major obstacle to the development of polymer electrolyte methanol fuel cells.

57 citations


Journal ArticleDOI
TL;DR: In this article, the effects of pretreatment of cast Nafion® films on the redox characteristics of Ru(bpy) 3 2+ (bpy = 2,2′-bipyridine) incorporated into the films were studied by in-situ spectrocyclic voltammetry (SCV) and photoluminescence.

56 citations


Journal ArticleDOI
TL;DR: In this article, a strong dependence of the thermal stability of Nafion perfluorosulfonate ionomer on the nature of the counterion associated with the fixed sulfonate site was reported.
Abstract: : We report in this paper a strong dependence of the thermal stability of Nafion perfluorosulfonate ionomer on the nature of the counterion associated with the fixed sulfonate site. These results were obtained using thermal gravimetric analysis on a series of alkali metal and alkyl ammonium cation- exchanged Nafion films. We have found that the temperature of decomposition of Nafion is inversely dependent on the size of the exchanged cation; i. e. Nafion films show improved thermal stability as the size of the counter cation decreases. We attribute this inverse relationship of thermal stability with counterion size to an initial decomposition reaction which is strongly influenced by the strength of the sulfonate-counterion interaction....Nafion, Thermal stability.

Journal ArticleDOI
TL;DR: An amperometric enzyme electrode for glucose was prepared by using a lipid-modified glucose oxidase and a perfluorinated ionomer (Nafion), which was applied to the determination of glucose in fruit juices; the Nafion coating was effective in suppressing the electrochemical interference by lascorbate in the samples as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this paper, a major improvement in the selectivity of carbon fiber microelectrodes for acetylcholine (Ach) and choline (Ch) as cationic amines is described.
Abstract: A major improvement in the selectivity of carbon fiber microelectrodes for acetylcholine (Ach) and choline (Ch) as cationic amines is described. The electrodes are coated with Nafion, a perfluorosulfonated polymer. This coating is practically impermeable to ascorbic acid (AA) and anionic biogenic amine metabolites. Nafion-coated fiber was characterized by cyclic voltammetry (CV). Selectivity and the dynamic range of these coated electrodes were evaluated using amperometric determination at a fixed potential of 1.2 V. The esterase activity was determined using choline sensor, and the relative slope values showed a fast response between 1 and 3 minutes. Calibration plots for Ach and choline showed a linearity range between 0.1 and 3 mM, with an increase of two orders of magnitude better than the previously used PVA-SbQ membrane. No response was obtained between 0.1 and 0.3 mM of AA conc. The procedure, in preparing this type of coated electrodes, indicates some attractive perspectives for its use, especially for in vivo monitoring.

Journal ArticleDOI
TL;DR: In this article, a pinhole-free polypyrrole/polyvinylsulphonate (PPSULPHONATE) membrane was developed using a new electromembrane cell and a new electrochemical controller.

Journal ArticleDOI
TL;DR: In this article, the properties of Nafion films on electrodes were studied as a function of the water content in the deposition solutions (0.1% nafion in mixed ethanol/water).
Abstract: The properties of Nafion films on electrodes were studied as a function of the water content in the deposition solutions (0.1% Nafion in mixed ethanol/water). The rate of loading and unloading (i.e., ion-exchange) of the complex ion RuCbpy) 3 2+ , loading into films which were thermally treated, and penetration of the anion Fe(CN) 6 4+ were examined. All these measurements show a nearly linear dependence of the voltammetric peak currents (for the oxidation of the incorporated ions) on the percentage of water in the deposition solutions. These results lead to the conclusion that films that are cast from solutions of higher water content have more «open» structures that allow faster diffusion of ions

Journal ArticleDOI
TL;DR: In this paper, Nafion® film Au disk electrodes were employed to catalyze the reduction of nitrate in concentrated sodium hydroxide solution, and the kinetic characteristics of this catalytic system have been determined by the techniques of rotating disk electrode voltammetry and cyclic voltammetric with the aid of the developed kinetic models.

Journal ArticleDOI
R. Mosdale1, Philippe Stevens
TL;DR: In this paper, a new method of preparation of Electrode/Membrane/Electrode (EME) assemblies for Proton Exchange Membrane Fuel Cells (PEMFC) has been developed.

Journal ArticleDOI
TL;DR: In this article, a Nafion-film-coated indium tin oxide (ITO) electrode was used for in-situ spectrocyclic voltammetric investigations under different pH conditions.



Journal ArticleDOI
TL;DR: In this article, the authors measured the resonant frequency and resistance of a Nafion-coated quartz crystal and measured the cyclic voltammograms in hydroquinone solution.

Journal ArticleDOI
TL;DR: In this paper, a uricase biosensor was constructed by using bovine serum albumin and glutaraldehyde as cross linker to immobilize Uricase on a glassy carbon electrode modified with Nafion and methyl viologen (MV).
Abstract: A uricase biosensor was constructed by using bovine serum albumin and glutaraldehyde as cross linker to immobilize uricase on a glassy carbon electrode modified with Nafion and methyl viologen (MV). A linear response of uric acid in serum was observed in a range of 1.0·10−3 to 5.0·10−6 mol/1 and the response time is 25 s. This biosensor has the advantage of high sensitivity, fast response as compared with previous sensors and low interferences.

Journal ArticleDOI
TL;DR: In this article, the swelling and transport behavior of cation exchange membranes (Nafion 417, Nafion 423 and KESD) in aqueous and methanolic solutions were investigated.

Journal ArticleDOI
TL;DR: When the Nafion/Methylene Blue (MB) films are fully hydrated, MB + and (MB + ) 2 are formed in the films similarly as in solution as mentioned in this paper.
Abstract: When the Nafion/Methylene Blue (MB) films are fully hydrated, MB + and (MB + ) 2 are formed in the films similarly as in solution. In addition, MBH 2+ also exists and increases with decreasing MB concentration. The hydration state of Nafion films is altered by equilibration with air streams of different relative humidities (RH). At a low MB concentration MBH 2 3+ together with MBH 2+ is formed in the low RH region, whereas both MB + and MBH 2+ are the main species in the high RH region

Journal ArticleDOI
TL;DR: The photophysical properties of quantized CdS clusters in a perfluorosulfonate polymer (Nafion) film have been investigated by time-resolved emission spectroscopy.
Abstract: The photophysical properties of quantized CdS clusters in a perfluorosulfonate polymer (Nafion) film have been investigated by time-resolved emission spectroscopy. The ultrasmall CdS clusters were prepared by exposing Cd2+-exchanged polymer film to H2S. Size-dependent absorption and emission properties were observed during the growth of these clusters. The emission decay is multiexponential with lifetimes ranging from 0.85 to 480 ns.

Journal ArticleDOI
TL;DR: In this paper, the kinetics of electron transfer between OS(bpy)33+ incorporated in Nafion® coatings on electrodes and IrCl63− anions in solution were examined by means of rotating disk voltammetry.

Journal Article
TL;DR: In this paper, a two-and four-electrode geometry was used to distinguish between the membrane impedance and the interfacial impedances, and it was shown that the impedance of Nafion for frequencies up to 100 kHz is characterized by a pure resistance, similar to conventional liquid electrolytes.
Abstract: AC impedance spectroscopy has been employed to study the conduction of protons in Nafion 117 polymer electrolyte membranes. Both two- and four-electrode geometries have been used to uniquely distinguish between the membrane impedance and the interfacial impedances. The results show that the impedance of Nafion for frequencies up to 100 kHz is characterized by a pure resistance, similar to conventional liquid electrolytes. The frequency dependent features observed using a two-electrode geometry are shown to be consistent with well-characterized interfacial impedances and do not arise from ionic conduction in the membrane. These results show that previous two-electrode studies reported in the literature have misinterpreted the impedance of the electrode interfaces as belonging to the conduction process in the electrolyte.

Journal ArticleDOI
TL;DR: In this paper, the catalysis of the reduction of dioxygen to hydrogen peroxide by different substituted 9-(4-R-phenyl)-N-methylacridiniums (R = H, Cl, F) was studied in homogeneous solutions and in Nafion® gel-modified electrodes.

Journal ArticleDOI
TL;DR: In this article, the absorption and fluorescence spectra of the title compounds have been investigated in solvents such as water, methanol and dioxan, in surfactants such as sodium dodecyl sulphate, cetyl trimethyl ammonium chloride and Triton X-100 and in a Nafion medium.
Abstract: The absorption and fluorescence spectra of the title compounds have been investigated in solvents such as water, methanol and dioxan, in surfactants such as sodium dodecyl sulphate, cetyl trimethyl ammonium chloride and Triton X-100 and in a Nafion medium. The spectral shifts in each case are compared and related to the properties of the medium. In aqueous and surfactant media, the maximum red shift in the absorption is observed for C153 and the absorption increases in the order C120, Cl, C102, C1F and C153. The fluorescence maxima also showed the same trend as the absorption shifts. Of the solvents, the least-polar solvent dioxan gave the maximum blue shift. In Triton X-100, the dyes registered the maximum blue shift. More or less the same trend is observed in both the absorption and the emission cases. In Nafion, C120 showed the maximum binding density of 3.58 × 10 −7 mol mg −1 and C1F showed the minimum binding density of 7.6 × 10 −8 mol mg −1 . The spectra of the dyes in Nafion exhibited unusual broadening both for absorption and for emission owing to the immobilization of the dyes in this medium of restricted geometry.

Journal ArticleDOI
TL;DR: In this paper, impedance techniques were employed to measure charge propagation rates in Nafion/Os (bipy) 3 3+/2+ and Nafions/C 5H 5 FeC 5 H 4 CH 2 N(CH 3 ) 3 2+/++ films on glassy carbon electrode surfaces and the observed dependencies were compared with the predictions of recent models that take into account the effects of intersite interactions, variations in non-redox counter-ion activity and ion-pair formation.