Showing papers on "Nafion published in 1996"
TL;DR: In this article, the proton conductivity of Nafion 117 was measured under various conditions of humidity and temperature using a four-electrode ac impedance method, and it varied strongly with the humidity and heat-treatment of the membrane.
Abstract: Nafion 117{reg_sign} is a proton conducting ion-exchange membrane which is now receiving much attention due to its use as an electrolyte in the polymer-electrolyte-membrane fuel cell (PEMFC), which is of great interest for electric vehicle propulsion. The proton conductivity of Nafion 117 was measured under various conditions of humidity and temperature using a four-electrode ac impedance method. The conductivity of this membrane without heat-treatment was ca. 7.8 {times} 10{sup {minus}2} S/cm at ambient temperature and 100% relative humidity; it varied strongly with the humidity and heat-treatment of the membrane. After heat-treatment, the membrane showed a slight dependence of conductivity on temperature. From 21 to 45 C, its conductivity at a given relative humidity decreased with increasing temperature, while from 45 to 80 C it increased with temperature.
851 citations
TL;DR: Nafion resin, a perfluorinated ion exchange polymer, has been used as a heterogeneous strong acid catalyst for a range of reactions; however, in nonpolar solvents or for gas phase reactions the act...
Abstract: Nafion resin, a perfluorinated ion-exchange polymer, has been used as a heterogeneous strong acid catalyst for a range of reactions; however, in nonpolar solvents or for gas phase reactions the act...
391 citations
TL;DR: In this paper, Nafion samples were loaded with fuel-cell grade platinum black and heated under atmospheres of nitrogen, 5% hydrogen, or air in a thermal gravimetric analyzer and the products of decomposition were taken directly into a mass spectrometer for identification.
Abstract: Nafion{reg_sign} is an important polymer electrolyte for polymer electrolyte fuel cell applications due to its inertness and high proton conductivity. Operation of these fuel cells for extended periods of time at temperatures approaching 100 C introduces concerns of the thermal stability of the Nafion electrolyte. To simulate the conditions in a fuel cell, Nafion samples were loaded with fuel-cell grade platinum black and heated under atmospheres of nitrogen, 5% hydrogen, or air in a thermal gravimetric analyzer. The products of decomposition were taken directly into a mass spectrometer for identification. In all cases, Nafion was found to be thermally stable up to 280 C, at which temperature the sulfonic acid groups began to decompose. A mechanism for the decomposition is proposed which explains many of the evolved compounds observed during heating.
274 citations
TL;DR: The findings showed that electrodes treated with Nafion first, followed by o-PD, were very sensitive to NO.
Abstract: Nitric oxide (NO•) sensors were prepared using o-phenylenediamine (o-PD) and Nafion to modify the surface of 30 μm diameter carbon fiber electrodes. These electrodes were compared with nickel porphyrin-type NO• sensors that have already been described. High-speed chronoamperometry, amperometry, and differential pulse voltammetry were used to compare the performance of sensors modified with various combinations of Nafion, o-PD, or nickel(II) meso-tetrakis(3-methoxy-4-hydroxyphenyl)porphyrin (Ni-TMPP), in order to determine which electrodes had the most sensitivity and selectivity for NO•. Our findings showed that electrodes treated with Nafion first, followed by o-PD, were very sensitive to NO•, with a detection limit of 35 ± 7 nM. In addition, o-PD electrodes were also very selective against ascorbate (>600:1), dopamine (>300:1), and nitrite (>900:1). Moreover, in the range of 0−6 μM NO•, o-PD electrodes displayed excellent linearity (R2 ≥ 0.997). In contrast, Ni-TMPP electrodes (with Nafion) had signific...
263 citations
TL;DR: In this paper, the electro-osmotic drag coefficient of water in two polymer electrolytes was experimentally determined as a function of water activity and current density for temperatures up to 200 C.
Abstract: The electro-osmotic drag coefficient of water in two polymer electrolytes was experimentally determined as a function of water activity and current density for temperatures up to 200 C. The results show that the electro-osmotic drag coefficient varies from 0.2 to 0.6 in Nafion{reg_sign}/H{sub 3}PO{sub 4} membrane electrolyte, but is essentially zero in phosphoric acid-doped PBI (polybenzimidazole) membrane electrolyte over the range of water activity considered. The near-zero electro-osmotic drag coefficient found in PBI indicates that this electrolyte should lessen the problems associated with water redistribution in proton exchange membrane fuel cells.
232 citations
TL;DR: In this paper, the average and local conductance of Nafion® 117 under different degrees of humidification was examined. But the authors focused on the ion transport characteristics of me membrane and did not consider the role of water content in the transport of H+ ions across the membrane in fuel cells.
192 citations
TL;DR: In this article, a vapor-feed direct methanol fuel cell based on a Nafion 117 solid polymer electrolyte was investigated, and the structure, surface, and morphology of the catalysts were investigated by X-ray powder diffraction, Xray photoelectron spectroscopy, and transmission electron microscopy.
Abstract: A vapor-feed direct methanol fuel cell based on a Nafion 117{reg_sign} solid polymer electrolyte was investigated. Pt-Ru/C and Pt/C catalysts were employed for methanol oxidation and oxygen reduction, respectively. The structure, surface, and morphology of the catalysts were investigated by X-ray powder diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Crystalline face-centered cubic phases were found in the Pt and Pt-Ru catalysts. The alloy composition in the Pt-Ru/C catalyst was different from the nominal composition, probably due to the formation of surface RuO{sub x} species, as indicated by X-ray photoelectron spectroscopy. Transmission electron microscopy observation showed an increase of the average particle size and particle agglomeration in the Pt-Ru/C catalyst compared to the Pt/C catalyst. The membrane/electrode assembly was prepared by using a paste process method. Scanning electron microscopy and energy dispersive X-ray analyses showed good adhesion of catalyst layers to the membrane and a homogeneous distribution of the ionomer inside the catalyst. AC-impedance and galvanostatic steady-state polarization techniques were used to investigate the electrochemical performance of the direct methanol fuel cell.
179 citations
TL;DR: The density of Nafion membranes wetted in water and acetonitrile and the solubility of NAFion in a 50:50 ethanol/water mixture are reported and recast membranes thermally processed for varying lengths of time were examined.
Abstract: The density of Nafion membranes wetted in water and acetonitrile and the solubility of Nafion in a 50:50 ethanol/water mixture are reported. Commercially available membranes, solution recast membranes, and recast membranes thermally processed for varying lengths of time were examined. Unheated recast membranes were found to be ∼20% less dense in water than both commercial membranes and recast membranes heated at 140 °C for 40, 50, and 60 min. For heating times of ≥40 min, the density of recast membranes in water was invariant and equal to the density of commercial films. Similarly, in acetonitrile, commercial membranes and films heated for 1 h had the same density; unheated recast films were ∼25% less dense. Nafion density in acetonitrile was ∼15% less than that in water. Acid pretreatment reduced Nafion film density by ∼15%. Unheated recast films were 22−100% soluble in a sonicated ethanol/water mixture. Commercial membranes and recast films heated for as little as 10 min were insoluble under the same co...
165 citations
TL;DR: In this article, the Nafion® 117 membrane in H 2 O 2 and H 2 air polymer electrolyte fuel cells (PEFCs) has been measured in situ using fast current pulses.
131 citations
TL;DR: Stable, functional composite films were made from the ionomer Nafion, water-insoluble surfactants, and heme proteins or the enzyme alcohol dehydrogenase as mentioned in this paper.
Abstract: Stable, functional composite films were made from the ionomer Nafion, water-insoluble surfactants, and heme proteins or the enzyme alcohol dehydrogenase. Rates of electron transfer between myoglobin (Mb) and hemoglobin (Hb) and edge plane pyrolytic graphite (PG) electrodes in these composite films were much larger than those for Hb and Mb in solution on Nafion-coated or bare PG electrodes. Films containing Nafion, didodecydimethylammonium bromide (DDAB), and hemoglobin or myoglobin retained about 90% of the initial redox activity during 4 weeks of storage at 4 °C. DDAB is arranged in lamellar liquid crystal bilayers in these films at 25 °C, which were more stable than films of the proteins and DDAB alone. Films of Nafion−lecithin−Cyt c on edge plane PG also had good electrochemical properties but were much less stable. Electronic and vibrational spectra indicate that the heme proteins are not denatured in the composite films, but conformational differences from the native state may exist. Linear dichroism...
121 citations
TL;DR: In this article, the area resistivities of the chlorosulfonated homogeneous polyethylene (PE) dense film and asymmetric membrane (MH-X) were tested as separators for the all-vanadium redox flow battery.
TL;DR: In this paper, a complete assignment of the IR spectra of the ionic and neutral hydrogen-bonded species formed by interaction of a series of bases of increasing proton affinity [methanol, ethanol, dimethyl ether, diethyl ether and tetrahydrofuran (THF)] with H-Y, H-ZSM-5, Hmordenite (H-Mord), and H-Nafion is given.
Abstract: A complete assignment of the IR spectra of the ionic and neutral hydrogen-bonded species formed by interaction of a series of bases of increasing proton affinity [methanol, ethanol, dimethyl ether, diethyl ether and tetrahydrofuran (THF)] with H-Y, H-ZSM-5, H-mordenite (H-Mord) and H-Nafion is given. Special attention is devoted to the discussion of spectral manifestations associated with structures varying with continuity from the true neutral AH⋯B form (low B proton affinity) to the true ionic A–⋯HB+ forms (high B proton affinity) passing through intermediate situations characterized by proton potentials with a single broad minimum or two minima separated by a low barrier (hesitating proton) and substantial ionic character. The assignment is based more on the comparison of the whole series of spectra than on the minute analysis of the specific properties of each spectrum. The assignment is also based on the comparison of the spectra of the adducts in zeolites with the spectra of analogous species formed in homogeneous conditions between acids and bases of comparable base and acid strengths (used as models).The main conclusions are: (i) adducts formed in H-Y have neutral AH⋯B character (only at the highest filling condition are signs of formation of ionic dimeric B⋯HB+ species observed for methanol and ethanol); (ii) the species formed upon adsorption of methanol and ethanol on H-ZSM-5 and H-Mord are neutral at low coverage and prevalently ionic at the highest filling conditions [because of the formation of (B)n⋯HB+ oligomers: 1, 2, …, n]; (iii) owing to the larger basicity of the ethers and THF, monomeric hydrogen-bonded adducts characterized by nearly symmetric proton potentials and substantial ionic character are directly formed on H-ZSM-5 and H-Mord without the intervention of other adsorbed molecules; (iv) THF and diethyl ether do not enter the H-Mord channels because the strongly adsorbed forms formed at the pore entrances block further penetration; (v) on the superacidic H-Nafion membrane (used as a model of a superacidic solid) all substrates directly form very strong and nearly symmetric hydrogen bonds without the assistance of other basic molecules: consequently the formed species always have prevalently ionic character even at the lowest dosages.
TL;DR: In this article, a perfluorinated cation exchange material (Nafion ®, DuPont) is evaluated for use as a vapour permeation membrane at temperatures up to 200°C.
TL;DR: In this paper, the electrical conductivity and proton and fluorine-19 NMR spin-lattice relaxation times (T1) in acid form NAFION 105, 117, and 120 conditioned at various levels of relative humidity have been carried out.
Abstract: Measurements of the electrical conductivity and proton and fluorine-19 NMR spin−lattice relaxation times (T1) in acid form NAFION 105, 117, and 120 conditioned at various levels of relative humidity have been carried out. Complex impedance studies were made along the plane of the polymer film at frequencies from 10 to 108 Hz at room temperature and pressures up to 0.3 GPa. The NMR measurements were made at room temperature and pressures up to 0.25 GPa. Both types of measurement were also carried out on various concentrations of sulfuric acid in water. The electrical conductivity decreases with increasing pressure for low water content acid solutions and low water content NAFION samples. This behavior (positive activation volumes) is that expected for “normal” liquids and for ions in polymers where the motion of the ions is determined by the host matrix. However, for high water contents, the reverse is true. The electrical conductivity increases with increasing pressure which gives rise to a negative activ...
TL;DR: Preliminary studies of cellular NO release from Rhodobacter sphaeroides bacterial cells with excellent results are carried out.
Abstract: Nitric oxide can be electrocatalytically reduced at electrodes modified with electropolymerized films of [Cr(v-tpy)2]3+. Upon further modification with a thin film of Nafion (to prevent interferences from anions, especially nitrite), these electrodes can be employed as NO sensors in solution with submicromolar detection limits and fast response. We have carried out preliminary studies of cellular NO release from Rhodobacter sphaeroides bacterial cells with excellent results.
TL;DR: In this article, the authors measured oxygen concentrations (C{sub b}) and diffusion coefficients (D) in various proton exchange membranes using chronoamperometry at microelectrodes, under conditions similar to those prevailing in proton-exchange-membrane fuel cells.
Abstract: Oxygen concentrations (C{sub b}) and diffusion coefficients (D) in various proton exchange membranes were measured using chronoamperometry at microelectrodes. These measurements were made under conditions similar to those prevailing in proton-exchange-membrane fuel cells. Knowledge of the D and C{sub b} parameters is essential for the determination of oxygen permeation in the catalytic layers of gas diffusion electrodes, which could be rate limiting in these low-temperature fuel cells. Furthermore, the D and C{sub b} values also provide the permeation rates of oxygen through the bulk of the proton conducting membrane. it was found that the concentration of oxygen increased and the diffusion coefficient decreased with increasing equivalent weight of the membranes. These results were interpreted using a model based on the microstructure of the swollen membranes separated into two phases, one hydrophobic and the other hydrophilic, with distinctly different O{sub 2}-permeation properties. According to this model the relative amounts of the two phases in the membranes, caused by the different water contents, determine the O{sub 2} solubility and diffusion coefficient in the different membrane materials.
TL;DR: The incorporation of Ru(bpy)2dppz2+ (Dppz = dipyrido[3,2-a:2,3,c]phenazine) into Nafion coatings was monitored in situ by electronic absorption, steady-state emission, and lifetime measurements as discussed by the authors.
Abstract: The incorporation of Ru(bpy)2dppz2+ (dppz = dipyrido[3,2-a:2‘,3‘-c]phenazine) into Nafion coatings was monitored in situ by electronic absorption, steady-state emission, and lifetime measurements. ...
TL;DR: In this article, Nafion-in situ sol-gel reactions were affected for Zr(OBu)4 that permeated low water content membranes unidirectionally and IR peaks reflecting ZrO2 and incomplete hydrolysis of ZrOBu groups near both surfaces were detected.
Abstract: Nafion-in situ sol-gel reactions were affected for Zr(OBu)4 that permeated low water content membranes unidirectionally. IR peaks reflecting ZrO2 and incomplete hydrolysis of ZrOBu groups near both surfaces were detected. Vibrations of Zr(OEt)4 detected near both sides arise from alkoxy exchange in the presence of the solvent EtOH. Unreacted alkoxy group bands are more distinct near the nonpermeated surface. An IR band for the ZnOBu group diminishes, whereas that for ZnOEt increases with increasing time near the permeated surface due to progressive alkoxy exchange. The ZrO2 band becomes more intense with time near the permeated surface. X-ray spectroscopy/scanning electron microscopy studies of Zr concentration across the membrane thickness verified compositional asymmetry. CO2 gas permeability versus upstream pressure plots are monotonically increasing, suggesting diffusion accompanied by complex plasticization. © 1996 John Wiley & Sons, Inc.
TL;DR: In this paper, the enzyme suspensions in concentrated ethanol solutions were prepared without any prior modifications of the protein, and the remaining activity after 30 min exposure to such solutions under optimal conditions was up to 100%.
Abstract: We propose immobilizing enzymes into Nafion membranes by suspending the enzyme in a water−ethanol mixture with a high (>90%) ethanol content, followed by mixing with the dissolved polyelectrolyte, and finally allowing the enzyme−polyelectrolyte solution to dry at the target surface (electrode surface). Since Nafion solution was deposited from a solution where it is truly dissolved and without excessive dilution with water, the resulting membranes were more uniform and stable than those otherwise obtained. Enzyme suspensions in concentrated ethanol solutions were prepared without any prior modifications of the protein. The remaining activity after 30 min exposure to such solutions under optimal conditions was up to 100%. The stability of the enzymes in these suspensions was higher than that in aqueous solution. Electrochemical biosensors made accordingly showed a several times increased response compared with those of enzyme electrodes based on the traditional way of using excessive dilution of Nafion with...
TL;DR: In this paper, a humidity sensor was fabricated by coating a surface plasmon waveguide with a thin layer of Nafion fluoropolymer, which is able to measure relative humidity over a range of at least 20% to 50%, while exhibiting good linearity.
Abstract: A humidity sensor has been fabricated by coating a surface plasmon waveguide with a thin layer of Nafion fluoropolymer. The refractive index of Nafion varies as a function of humidity, causing a shift in the plasmon resonance wavelength. The present device is able to measure relative humidity over a range of at least 20% to 50%, while exhibiting good linearity. Furthermore, humidity-induced index changes to Nafion occur rapidly and appear to be fully reversible.
TL;DR: In this paper, the ion exchange isotherm of the Nafion R 117 membrane in contact with [NaCl] + 2[CaCl 2 ] = 0.1 M.
TL;DR: In this article, a cyclic potential scan and a constant potential were evaluated to form a deposit, with Pt loadings ranging for each from 60-750 μg Pt cm −2 GC obtained by varying the coulombs discharged.
TL;DR: A novel Nafion/clay-modified electrode (NCME) was developed for the determination of paraquat by square-wave cathodic stripping voltammetry and the clay that showed the best performance is nontronite (SWa-1, ferruginous smectite).
Abstract: A novel Nafion/clay-modified electrode (NCME) was developed for the determination of paraquat by square-wave cathodic stripping voltammetry. The clay that showed the best performance for the fabrication of the NCME is nontronite (SWa-1, ferruginous smectite). The electrochemical behavior of paraquat showed that the cathodic peak at -0.70 V vs Ag/AgCl permits adequate quantification of the analyte. Linear calibration curves are obtained over the 0-80 ppb range, with a detection limit of 0.5 ppb in pH 8 phosphate buffer solution for 4 min preconcentration time. Various factors influencing the determination of paraquat were thoroughly investigated in this study. The practical analytical utility is illustrated by selective measurements of paraquat in real water samples.
TL;DR: In this paper, a facilitated transport model for CO 2 through ion exchange membranes containing a diamine complexing agent was developed, where diamine ion behaves as a mobile carrier for CO2.
TL;DR: Nafion enhances selectivity for glutamate over test species that include ascorbic acid, uric acid and acetaminophen, and the extent of this enhancement depends on the thickness of the Nafion layer.
TL;DR: In this article, the water transference coefficients of Nafion 117 equilibrated with solutions of aliphatic ammonium chlorides which have both hydrophilic and hydrophobic parts increased with the increase in the size of ammonium cations, which was definitely opposite to the trends observed in the case of alkali and alkaline earth metal cations.
TL;DR: In this paper, a spin-coating process was used to add additional Nafion or PVP (poly (4-vinylpyridine-co-styrene)) membranes on top of the urea microsensor.
TL;DR: Nafion-coated mercury thin film electrodes have been evaluated for use in batch-injection analysis with anodic stripping voltammetry (BIA-ASV) and their effect was found to be much less with the Nafion film coating.
TL;DR: In this paper, the dimerization of α-methylstyrene was examined at 50°C and 1 atm in nonpolar cumene and polarp-cresol solvents, using both soluble liquid acids and resin-based solid acids as catalysts.
TL;DR: In this paper, carbon monoxide sensors using Nafion solid polymer electrolyte are described, and the proposed manufacturing technology is compatible with hybrid technology, which is suitable for cheap mass fabrication.
Abstract: Carbon monoxide sensors using Nafion solid polymer electrolyte are described. Dry Nafion sensors showed stability problems; on the other hand sensors equipped with a water reservoir (wet Nafion sensors) were extremely stable. The proposed manufacturing technology, compatible with hybrid technology is suitable for cheap mass fabrication.