Showing papers on "Nafion published in 1989"

Fresh look at transport in perfluorosulfonate ionomers: ultramicroelectrode investigations of Nafion and the Dow ionomers

Abstract: : Chronoamperometry at ultramicroelectrodes is a powerful and convenient technique for the determination of apparent diffusion coefficients and concentrations of electroactive cations ion-exchanged into Nafion and Dow perfluorosulfonate films. This technique offers tremendous advantages over the conventional electrochemical methods which employ film coated macro sized electrodes. These advantages stem from the elimination of iR distortion at the ultramicroelectrode and from the ability to determine both the concentration and apparent diffusion coefficient of the electroactive cation from a single experiment. Further improvements over the conventional approach were achieved by eliminating coupled diffusion and migration contributions to the measured current response. Under these conditions, charge is transported via ionic diffusion rather than through electron hopping. Furthermore, the apparent diffusion coefficients decrease with increasing concentration of the electroactive cation in the film.

The Molecular‐Level Interpretation of Salt Uptake and Anion Transport in Nafion Membranes

Abstract: Etude theorique de la captation des sels cationiques dans une membrane electrode en nafion. Equilibre entre l'electrode et l'electrolyte. Determination a l'aide d'une equation empirique du transport anionique a l'interieur de l'electrode.

Kinetics of Fuel Cell Reactions at the Platinum/Solid Polymer Electrolyte Interface

Abstract: Platinum gauze electrodes coated with the proton-conducting polymer, Nafion, were investigated with respect to the kinetics of the oxygen reduction and hydrogen oxidation reactions. The coated electrodes were in contact with a Nafion membrane electrolyte. The current-potential behavior of the coated electrodes depended upon the thickness of the coating. The electrodes with thicker coatings exhibited less activation and ohmic control but encountered diffusion limitations. Those with thinner coatings showed significant ohmic control. A theoretical analysis was made for the current potential relation and the current distribution using a model of a Nafion-coated wire in contact with the membrane. The present analysis confirms the necessity of optimizing the amount of Nafion impregnation in low-Pt-loads, porous gas-diffusion electrodes, as was experimentally observed in another study in the authors' laboratory.

Platinum-dispersed Nafion film modified glassy carbon as an electrocatalytic surface for an amperometric glucose enzyme electrode

Abstract: A Nafion film dispersed with platinum particles formed on a glassy carbon electrode combines the electrocatalytic activity of platinum with the background stability of glassy carbon. It serves as a selective and sensitive electrode surface for an amperometric glucose enzyme electrode. Details on the construction and the functional characteristics of the enzyme electrode are described. It is shown that the electrode is well suited to the determination of levels of glucose in blood by flow injection with amperometric detection.

Voltammetry in supercritical carbon dioxide at platinum microdisk electrodes coated with perfluorinated ion-exchange membranes

Abstract: It has previously been shown that the resistance of supercritical CO 2 is too high for voltammetry, even with microelectrodes, unless electrolytes and/or polar modifiers are present in the fluid. In a supercritical fluid flow system, such as chromatography, the use of an added electrolyte is not desirable. As an alternative, a film of an ionically conducting polymer, Nafion, placed over an electrochemical probe consisting of both a microdisk working electrode and a quasi-reference electrode, has been used. Undistorted voltammograms of ferrocene, 4-methylcatechol and 3,4-dihydroxy-benzylamine dissolved in supercritical CO 2 in the presence of small quantities of H 2 O have been obtained without the use of added supporting electrolyte. Experiments carried out in a supercritical fluid flow stream demonstrate the potential utility of membrane coated microelectrodes as chromatographic detectors

Nafion‐like thin film plasma‐polymerized from perfluorobenzene/SO2 mixture

Abstract: Plasma polymerization of perfluorobenzene/sulfur dioxide (PFB/SO2) mixture was investigated by elemental analysis, infrared spectroscopy, and XPS. Plasma polymer films like Nafion were obtained from the plasma polymerization of PFB/SO2 mixture. The plasma polymerization deposited fluoropolymers with sulfur moieties including sulfonate and sulfonic acid groups. The elemental composition, F/C, and S/C atomic ratio of the formed plasma polymers were 0.65–0.67 and 0.24–0.27, respectively, which were independent of the starting mixture composition. The polymers showed cation-exchange ability of which the capacity was 0.49 meq/g polymer, and initiated the polymerization of pyrrole.

A Nafion¬-bound platinized carbon electrode for oxygen reduction in solid polymer electrolyte cells

Abstract: A full-factorial statistical method has been used to optimize the amount of binder, the compaction load and the compaction time in order to fabricate Nafion®-bound carbon electrodes containing platinum and pyrolysed cobaltmeso-tetramethoxyphenylporphyrin (CoTMPP). These electrodes are designed for oxygen reduction in solid polymer electrolyte fuel cells, and it has been found that incorporation of Nafion® gel with the carbon substrate facilitates its binding with the Nafion® membrane of such a fuel cell. The polarization behaviour of a Nafion®-bound carbon electrode containing platinum is compared to that containing pyrolysed CoTMPP.

One-step electrosynthesis and characterization of poly(aniline)–Nafion and poly(3-methylthiophene)–Nafion composite films

Abstract: Impregnated polymer composites, poly(aniline)–Nafion and poly(3-methylthiophene)–Nafion have been electrosynthesized from a solution containing a perfluorosulphonated ionomer (Nafion) as the only electrolyte and the monomer precursor of the electronically conducting polymers : poly(aniline) or poly(3-methylthiophene).

Electrochemical speciation analysis of metals at membrane-coated electrodes

Abstract: Speciation of model Cu complexes on the basis of size and charge was achieved by anodic stripping voltammetry (ASV) at mercury film electrodes (MFE) coated with Nafion or cellulose acetate Nafion (CANMFE). The Nafion-coated MFE effectively excludes negatively charged Cu complexes, and evidence for the containment of the diffusion layer beneath the Nafion coating is provided. The CANMFE excludes complexes with molecular weights greater than 200, including the Cu-fulvic acid complex, which is of particular interest for speciation in natural waters. Complexation titrations of fulvic acid with Cu show the unsuitability of differential pulse ASV for providing a realistic estimate of the end point (complexation capacity). Differential pulse polarography, which provides results more comparable with bioassays, can be used for the determination of complexation capacity. Results for the speciation analysis of coastal seawater and polluted fresh water are presented. The CANMFE is insufficiently sensitive for seawater analysis, but in polluted fresh water its use indicates that organic and inorganic complexes with molecular weights greater than 200 dominate the speciation for Cd (72%), Pb (96%), and Cu (> 99.8%).

Ionic conductivity of perfluorinated ionomer solutions and gels

Abstract: Conductivity measurements were made on stable solutions or gels of Li Nafion 1100 obtained by a recently reported process of solubilization of perfluorosulfonated ionomers in organic media The influence of the solvent characteristics was shown by usingN-methylformamide, propylene carbonate and triethylphosphate as solvents The temperature, between 25 and 80°C, the concentration, in the 0007–037m range and water effects on the electrical properties were studied The frequency dependence was measured in a 0163m solution inN-methylformamide from 156 Hz to 16 kHz Conductivities at zero concentration are discussed using the treatment of simple salts and data from the literature Li Nafion 1100 is well dissociated inN-methylformamide, giving a solution of higher conductivity (∼10−3 S cm−1) than in propylene carbonate and in triethylphosphate The mobility of the R-SO 3 − group is explained by the variation of the conductivity with frequency Activation energies are interpreted as resulting from the viscous forces within the solutions

Determination of catecholamines by an electrochemical flow-through detector with indium-tin oxide microelectrode arrays coated with Nafion.

Abstract: An electrochemical flow-through detector with indium–tin oxide interdigitated microelectrode arrays was used for the determination of catecholamines. This detector showed amplification of the current signals by redox cycling. The undesired response due to ascorbic acid can be eliminated by coating the electrode surface with Nafion.

Determination of Ammonia/Air Diffusion Coefficient Using Nafion Lined Tube

Abstract: Trace gaseous ammonia in air was removed in a laminar flow Teflon tube lined with Nafion film. The ammonia deposition pattern was obtained by sectioning the Nafion lining, extracting with an aqueous solution, and measuring the concentration with an ammonia gas electrode. Mass transport analysis of the deposition pattern demonstrated that the ammonia was removed from the air stream at a rate controlled by gaseous diffusion. The ammonia/air diffusion coefficient equalled 0.228 ± 0.012 cm2 s−1 at 1 atm 25°C. No dependence on relative humidity was observed over the range 10–92%.

The state of hydrated vanadyl ions adsorbed on a perfluorinated ionomer as studied by ESR and ENDOR

Abstract: Les ions VO 2+ sont employes comme marque pour etudier le mouvement de l'eau adsorbe sur une membrane Nafion

Electrochemical behaviour of nafion gels loaded with ferrocene and copper(I) diphenylphenathroline complexes

Abstract: Nafion gels made with hydrophobic solvents can be loaded with electroactive compounds such as ferrocene and behave as electrode coatings which exhibit the mechanical properties of a solid polymer and the electrochemical properties of an electrolytic solution.