Showing papers on "Nafion published in 1991"
TL;DR: In this paper, the concentration and diffusion coefficient of oxygen in Nafion, and the electrode kinetic parameters for the reduction of oxygen at the Pt/Nafion interface under totally solid-state conditions (i.e., no contacting liquid electrolyte phase).
Abstract: This paper reports on research in solid polymer electrolyte fuel cells gaining momentum because of the prospects of attaining high energy efficiencies and power densities essential for transportation and space applications. The most advanced solid polymer electrolytes for these fuel cells are the perfluorosulfonate ionomers (PFSIs), such as Du Pont's Nafion and the Dow PFSIs. The high oxygen solubility, chemical stability, proton conductivity and permselectivity exhibited by Nafion and the Dow PFSIs make them ideal candidates as electrolytes for fuel cells. Furthermore, the minimal anion adsorption on the Dow PFSIs make them ideal candidates as electrolytes for fuel cells. Furthermore, the minimal anion adsorption on electrodes from fluorinated acids enhances oxygen reduction kinetics. The objectives of this work were to determine the concentration and diffusion coefficient of oxygen in Nafion, and the electrode kinetic parameters for the reduction of oxygen at the Pt/Nafion interface under totally solid-state conditions (i.e., no contacting liquid electrolyte phase). Cyclic voltammetric and potentiostatic transient measurements were made at the Pt/Nafion interface. From cyclic voltammetric measurements, the purity of Nafion was ascertained and the roughness factor of the electrode was calculated. The slow sweep experiments yielded the Tafel parameters for oxygen reduction. From the two-section Tafelmore » plot, the calculated exchange current densities were found to be higher than those obtained at any other Pt/acid interface. From an analysis of the potentiostatic transients, the calculated values of oxygen solubility and diffusion coefficient in Nafion were higher than previously reported. These differences in mass-transfer data were attributed to differences in water content of the Nafion membrane.« less
230 citations
115 citations
TL;DR: In this article, a highly sensitive and selective electrochemical (LCEC) detector was developed for the liquid chromatographic (LC) analysis of carbohydrates, based on the catalytic oxidation of various sugars in alkaline solutions at a pH greater than 13.
Abstract: A highly sensitive and selective electrochemical (LCEC) detector has been developed for the liquid chromatographic (LC) analysis of carbohydrates. This detector consists of copper/copper oxide particles dispersed in a Nafion films that is cast onto the surface of a glassy carbon electrode. The copper is electrochemically deposited into the Nafion by a constant potential method. The response of the detector is based on the catalytic oxidation of various sugars in alkaline solutions at a pH greater than 13
95 citations
TL;DR: Nafion polymer exhibits sufficient biocompatibility to make it a viable candidate for some implantable biosensor applications, but it may, however, be necessary to compensate for the effect of the progression of fibrous encapsulation on sensor performance, particularly during the acute response stage.
88 citations
TL;DR: In this article, the authors used hyper-Lorentzian line shapes to simulate the motion of a polymer molecule (backbone and pendant chains) in Nafion solutions and corresponding membranes swollen by water, formamide, methanol and ethanol.
Abstract: Acid Nafion solutions and corresponding membranes swollen by water, formamide, methanol, and ethanol were studied to assess the mobility of the perfluorinated chains in the solutions. In ethanol solutions the NMR results suggest a nearly isotropic motion of the polymer molecule (backbone and pendant chains), with τ c ≤10 −4 s. The spectra of the swollen membrane, are intermediate between the spectra of the dry membrane and of the solutions. The spectra of the solutions and of the swollen membranes at ambient temperature, as well as the spectra of the dry membranes and of Teflon as a function of temperature, have been simulated by use of hyper-Lorentzian line shapes. An Arrhenius plot of the line width in dry Nafion vs temperature allows determination of the activation energy for the motion
83 citations
TL;DR: Nafion, a perfluorosulfonated ion-exchange polymer, has been evaluated as a substrate for immobilizing a near-infrared absorbing fluorophore to determine pH in solutions.
Abstract: Nafion, a perfluorosulfonated ion-exchange polymer, has been evaluated as a substrate for immobilizing a near-infrared absorbing fluorophore to determine pH in solutions.
74 citations
TL;DR: The results show that Nafion is a suitable polymeric surface for the attachment and growth of human cells, including endothelial cells.
72 citations
TL;DR: In this paper, Nafion-H, a perfluorinated resinsulfonic acid, was used to catalyse Friedel-Crafts benzylation of benzene and substituted benzenes with benzyl alcohols under relatively mild experimental conditions.
Abstract: Nafion-H, a perfluorinated resinsulfonic acid, catalyzes Friedel-Crafts benzylation of benzene and substituted benzenes with benzyl alcohols under relatively mild experimental conditions. Reactions are clean, and water formed as a byproduct does not deactivate the catalyst. It was also found that this method is applicable to the intramolecular cycloalkylation and oligomerization of methoxybenzyl alcohols
65 citations
54 citations
TL;DR: In this paper, an outer layer of the perfluorinated polysulfonate cation exchange polymer Nafion was applied to a Prussian blue film and the methyl viologen dication (colorless)/radical cation (purple) system was then incorporated by ion-exchange into the nafion.
Abstract: The results reported here demonstrate that such polychromicity can be further extended to include a purple color state. The method involves application of an outer layer of the perfluorinated polysulfonate cation exchange polymer Nafion to a Prussian blue film. The methyl viologen dication (colorless)/radical cation (purple) system is then incorporated by ion-exchange into the Nafion
52 citations
TL;DR: A combination of electrochemical and microgravimetric techniques, utilizing the electrochemical quartz crystal microbalance (EQCM), has been employed to study the ion transport behavior of polypyrrole films, prepared with a variety of electrolytes, during redox switching as discussed by the authors.
Abstract: A combination of electrochemical and microgravimetric techniques, utilizing the electrochemical quartz crystal microbalance (EQCM), has been employed to study the ion transport behavior of polypyrrole films, prepared with a variety of electrolytes, during redox switching. Systems investigated include poly(pyrrole chloride), poly(pyrrole dodecylsulfate), poly{pyrrole-co-[3-(pyrrol-1-y1)propanesulfonate]}, and polypyrrole/Nafion composites. It has been demonstrated that controlled ion transport properties of polypyrrole can be achieved by incorporating properly selected dopant anions into the polypyrrole film during electrosynthesis.
TL;DR: In this article, an efficient and mild procedure for the ring closure of 2,2'-dihydroxybiphenyls in the presence of the solid superacid Nafion-H (a solid perfluorinated resinsulfonic acid) to afford dibenzofuran derivatives in good to moderate yields
Abstract: We report an efficient and mild procedure for the ring closure of 2,2'-dihydroxybiphenyls in the presence of the solid superacid, Nafion-H (a solid perfluorinated resinsulfonic acid) to afford dibenzofuran derivatives in good to moderate yields
TL;DR: In this article, the Raman spectrum of a Nafion 117 membrane immersed in aqueous solution was recorded and the interaction of counter ions and also of sorbed electrolytes with the antagonist group SO3− of the membrane was studied.
Abstract: The Raman spectrum of a Nafion 117 membrane immersed in aqueous solution was recorded. Assignments are proposed for the fundamental vibrations observed for this material. The interaction of counter ions (cations) and also of sorbed electrolytes with the antagonist group SO3− of the membrane were studied. For this purpose, intensity measurements were made of selected appropriate signals versus the nature and type of counter ions (monovalent, divalent). The intensity of the symmetric stretching vibration band of the SO3− group can be used to monitor the variation of the conductivity of the membrane studied.
TL;DR: In this article, the transport properties of the cationic dyes methylene blue, thionine, safranine and meldola blue in Nafion-coated electrodes are reported.
TL;DR: In this article, an amperometric sensor for the determination of sulphur dioxide in both gaseous atmospheres and solutions of low conductivity is described, which consists of a porous Pt electrode (facing the sample) supported on one face of an ion-exchange membrane (Nafion 417) which serves as a solid polymer electrolyte.
Abstract: An amperometric sensor is described for the determination of sulphur dioxide in both gaseous atmospheres and solutions of low conductivity. It consists of a porous Pt electrode (facing the sample) supported on one face of an ion-exchange membrane (Nafion 417) which serves as a solid polymer electrolyte. The other side of the membrane faces an internal electrolyte solution (1 mol dm–3 aqueous perchloric acid) containing the counter and reference electrodes. This sensor is inserted into a flow cell in which gaseous or electrolyte-free aqueous samples are fed by a peristaltic pump placed in a closed-loop path and SO2 is oxidized at an applied potential of 0.65 V versus Ag–AgCl. The device is found to be characterized by a high current sensitivity and a short response time, 24 A cm–2 mol–1 dm3 and 1 s respectively for gaseous samples; (0.4 A cm–2 mol–1 dm–3 and 4 s, respectively, for water solutions), and by good stability and low background noise. The dynamic range extends up to 2 × 10–4 mol dm–3(gaseous samples) and 1 × 10–3 mol dm–3(water samples) with good linearity, and detection limits of 8 × 10–9 mol dm–3(gaseous samples) and 4 × 10–7 mol dm–3(water samples) are predicted for a signal-to-noise ratio of 3. The advantages offered by this type of sensor over conventional gas-permeation membrane electrodes are discussed.
TL;DR: PANI-Nafion membranes were prepared by a chemical method in which the faces of a commercial Nafion membrane were contacted with two acid solutions containing an oxidant (Fe3+) and aniline respectively as mentioned in this paper.
TL;DR: In this paper, a composite with polyaniline and Nafion, a strong acid-containing polymer, was made by reacting aqueous HCl/anilines and oxidizing agent solutions which were diffused in a nafion® film.
TL;DR: In this paper, the carotenoid cation radicals have been observed at 120 K, by EPR and proton ENDOR measurements, to be formed upon 77 K photolysis of thin films of Nafion or silica gel coated with the Carotenoids, β-carotene and canthaxanthin.
TL;DR: In this article, a polyaniline-Nafion composite electrode was used as an electrochemical detector for detecting alkali and alkaline earth metal ions using flow-injection analysis and ion chromatography.
TL;DR: The membrane permselectivities of several bilayer perfluorinated ionomer chloralkali membranes have been measured using a sodium ion radiotracer method with an automated laboratory electrolysis cell.
Abstract: The membrane permselectivities of several bilayer perfluorinated ionomer chlor‐alkali membranes have been measured using a sodium ion radiotracer method with an automated laboratory electrolysis cell. The influence of solution concentrations, electrode‐membrane gap, and solution mixing were evaluated for membranes which differed with regard to fabric reinforcement and surface smoothness. Results indicate that these cell and membrane‐related factors all influence membrane permselectivity in an operating cell, with certain practical consequences. The underlying reasons for this complex behavior are discussed.
TL;DR: In this paper, five types of chemically modified electrode (CMEs) prepared with the deposition of platinum particles on various surfaces of glassy carbon (GC) modified with cobalt porphyrin and Nafion® solution are characterized using the electron scanning microscope (SEM).
TL;DR: In this paper, a selective method based on the chemical reactivity of an immobilized modifier, 2,2-bipyridyl, toward cobalt (II) ion to yield the corresponding cation complex ((Bpy) 3 Co) 2+, which is taken up by another modifier, perfluoronated sulfonated polymer (Nafion).
Abstract: This selective method is based on the chemical reactivity of an immobilized modifier, 2,2-bipyridyl, toward cobalt (II) ion to yield the corresponding cation complex ((Bpy) 3 Co) 2+ , which is taken up by another modifier, perfluoronated sulfonated polymer (Nafion). Differential pulse voltammetry is employed, and the oxidation of the complex, at +0.1 V vs SCE, is observed. For a 5-min preconcentration period, a linear calibration curve is obtained for cobalt concentrations ranging from 7×10 −7 to 1×10 −5 mol/L, and the detection limit is 3×10 −7 mol/L
TL;DR: In this paper, a microcarbon array electrode was modified by the placement of a Nafion film containing cobalt tetramethylpyridyl phorphyrin on its surface.
Abstract: A microcarbon array electrode was modified by the placement of a Nafion film containing cobalt tetramethylpyridyl phorphyrin on its surface. This electrode was applied to the analysis of solution glucose when it was further modified by the immobilization of glucose oxidase on the outermost surface of the Nafion by the cross-linking of serum albumin with glutaraldehyde. The concomitant decrease in the concentration of oxygen, as it was consumed in the enzymatic reaction of glucose with glucose oxidase, was determined by either cyclic voltammetry or a double potential step method at the porphyrin-Nafion catalytic electrode. Glucose could be determined in the range of 0.01-4 mM rapidly, without interference from substances such as ascorbate or other saccharides.
TL;DR: In this paper, a new technique based on spectroscopic observation of the monomer/dimer equilibria of the reduced viologens yields apparent diffusion coefficients (D app ) of the radicals in Nafion.
Abstract: The diffusion of three viologens with differing overall charges has been studied in Nafion-modified electrodes. A new technique based on spectroscopic observation of the monomer/dimer equilibria of the reduced viologens yields apparent diffusion coefficients (D app ) of the radicals in Nafion. D app is found to be dependent on the concentration of the viologen species. It is proposed that the hydrophilic channels in Nafion play a significant role in determining D app and that physical diffusion and not electron hopping appears to be the main charge-transport mechanism
TL;DR: In this article, the influence of various preliminary experimental conditions on the selectivity of a Nafion-coated electrode in the flow-through determination of cationic drugs was investigated.
TL;DR: In this article, the gradual replacement of oxygen ligands around Cu 2+ with nitrogen ligands in Nafion soaked with acetonitrile has been deduced from ESR spectra at L-, S-, C-, and X-bands and from computer simulations.
Abstract: The gradual replacement of oxygen ligands around Cu 2+ with nitrogen ligands in Nafion soaked with acetonitrile has been deduced from ESR spectra at L-, S-, C-, and X-bands and from computer simulations. Results suggest that after one cycle of drying and soaking of the membranes with acetonitrile, Cu 2+ has two 14 N ligands in CH 3 CN and none in CD 3 CN. The isotope effect is assigned to the difference in the solvation energies of the sulfonic groups and of cations with deuteriated and protiated solvents
TL;DR: In this article, a theoretical model was developed to predict the temperature profiles across a Nafion membrane during Solid Polymer Electrolyte water electrolysis, and Infra-red analysis was used to check the validity of the model.
TL;DR: In this article, the characteristics and applicability of a Nafion-copper modified electrode for the determination of some sugars in food samples are described. And the analytical utility of the polymer-coated electrode is demonstrated by application to wine and milk samples.
Abstract: The characteristics and applicability of a Nafion-copper modified electrode for the determination of some sugars in food samples are described. Coating with a Nafion membrane and subsequent immersion in a copper solution provides a good barrier against many electroactive hydroxyacids commonly found in food samples. The Nafion modified electrode is stable, can be easily renewed, and shows reproducible results. The analytical utility of the polymer-coated electrode is demonstrated by application to wine and milk samples.
TL;DR: In this paper, the methylene blue (MB) sensitized photooxidations of anthracene, 9,10-diphenyl-anthracene (DPA), and 2-dimethylaminoanthracenes (DMA) have been studied in ethanol and in Nafion, a perfluorinated polymer with sulfonate groups.
Abstract: The methylene blue (MB) sensitized photooxidations of anthracene (AN), 9,10-diphenyl-anthracene (DPA) and 2-dimethylaminoanthracene (DMA) have been studied in ethanol and in Nafion, a perfluorinated polymer with sulfonate groups. Spectroscopic studies indicate that the incorporated chromophores are heterogeneously distributed in the micelle-like polymer. The uncharged aromatic hydrocarbons are located in the non-polar polymer backbone region while the positively charged species reside at the interface of aqueous cluster regions in the membrane. The MB-sensitized photooxidations of all anthracenes are faster in Nafion than in ethanol. Furthermore the photooxidation of AN is 1.6 times higher in D2O-swollen Nafion than in H2O-swollen samples. Analysis of the photodegradation data suggests that these results can be attributed to the heterogeneous siting of the chemical species and the behaviour of singlet oxygen in the membrane.