Showing papers on "Nafion published in 1990"

Microstructural evolution of a silicon oxide phase in a perfluorosulfonic acid ionomer by an in situ sol-gel reaction. 3. Thermal analysis studies

Abstract: Microcomposite membranes were produced via the in situ diffusion-controlled, acid-catalyzed sol-gel reaction for tetraethoxysilane in prehydrated and methanol-swollen Nafion perfluorosulfonic acid films. The thermal behavior of these microcomposites was investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). It was found by TGA that significant

A biocompatible enzyme electrode for continuous in vivo glucose monitoring in whole blood

Abstract: Electrode fouling and biocompatibility problems remain the greatest obstacles to developing a stable glucose sensor for continuous in vivo monitoring in whole blood. Nafion encapsulation successfully prevents electrode fouling, and substantially inproves the stability and performance of whole blood and plasma glucose sensors in vitro . Results are presented which indicate that Nafion also provides a biocompatible interface with the body, and hence offers the potential for use with implantable sensors. A biocompatible enzyme electrode system is proposed, based on Nafion polymer encapsulation, which has a suitable size and geometry to be tested as an implantable sensor for long-term use. A custom-designed CMOS integrated potentiost was used to evaluate the electrode response in whole blood.

Development of Biosensors Based on Immobilization of Enzymes in Eastman AQ Polymer Coated with a Layer of Nafion

Abstract: A fast and simple procedure to prepare enzyme electrode is presented herein. A blend of amorphous polyester cationic exchangers (AQ 29D:AQ 55D; ratio 1:1) dispersed in water has been used for the immobilization of l-amino acid, choline, galactose or glucose oxidase enzymes at the surface of a platinum electrode. The resulting polymer-enzyme film was covered by a thin layer of Nafion to avoid its subsequent dissolution in water. The assays are based on the electrochemical detection of enzymatically generated hydrogen peroxide. Good amperometric responses were obtained with each of these enzyme electrodes. The major advantage in using this water dispersed polymer lies in its ability to dissolve the enzyme without any significative loss of enzymatic activity.

Surface-enhanced Raman scattering of dopamine at polymer-coated silver electrodes.

Abstract: Attenuation of dopamine surface-enhanced Raman scattering (SERS) spectra at silver electrodes by protein adsorption is described. Polymer-modified electrodes eliminate protein adsorption effects. Partially hydrolyzed cellulose acetate coatings prevent protein adsorption and allow transport of dopamine to and from the electrode surface. Dopamine SERS spectra from these electrodes are similar to those obtained at uncoated electrodes. Perfluorosulfonate (Nafion) coatings also prevent protein adsorption. However, dopamine transported to the electrode remains trapped inside the coating and cannot be removed.

Ion Transporting Composite Membranes II . Ion Transport Mechanism in Nafion‐Impregnated Gore‐Tex Membranes

Abstract: Our previous report suggested that Ru(NH 3 ) 6 3+ diffusion coefficients are higher in Nafion TM1 -impregnated Gore-Tex (NIGT) membranes than in bulk Nafion membranes. This paper focuses on the mechanism of Ru(NH 3 ) 6 3+ transport in NIGT membranes. We investigate the dependencies of the diffusion coefficients on the concentration of the electroactive species and on the weight fraction of Nafion in NIGT membranes. The apparent diffusion coefficients for Ru(NH 3 ) 6 3+ and Ru(NH 3 ) 3 2+ are directly proportional to the inverse weight fraction of Nafion in the NIGT membrane. We propose that the diffusion of the ions are coupled between the ions residing in the solution phase and the ions electrostatically bound to SO 3 − sites in the Nafion phase. By controlling the weight fraction of the Nafion in the NIGT membranes, we are able to vary Ru(NH 3 ) 6 3+ and Ru(NH 3 ) 6 2+ diffusion coefficients from 3×10 −8 cm 2 /s to 3×10 −7 cm 2 /s

Ultrasmall particles of CdSe and CdS formed in Nafion by an ion-dilution technique

Abstract: The transition of semiconductor chalcogenides from molecular CdX (X = Se, S) to bulk material has been observed in Nafion, a cation-exchange membrane. The two-phase structure of Nafion, consisting of a hydrophobic region and ionic clusters, has been utilized to form ultrasmall particles of CdS/Se by using a technique analogous to an inverted micelle microemulsion method, where the Cd ion/ionomer cluster ratio is controlled by diluting the cadmium-exchange solution with an inert ion (Ca{sup 2+}). The absorption onset for the cadmium chalcogenides formed ban be tuned over a range of more than 3.5 eV by varying the Cd{sup 2+}Ca{sup 2+} ratio in the solution used to exchange the acidic form of the ionomer membrane.

A Pronounced Catalytic Activity of an Acidic Cesium Salt of 12-Tungstophosphoric Acid for Ester Decomposition in Solid–liquid System

Abstract: The acidic Cs salt of 12-tungstophosphoric acid (Cs/polyanion = 2.5) was much more active for liquid phase decomposition of cyclohexyl acetate than Nafion, HY-zeolite, H-ZSM-5, Al3+-exchanged montmorillonite, and SO42−/ZrO2.

Infrared reflectance absorption spectroscopy (IRRAS). Study of the thermal stability of perfluorinated sulphonic acid ionomers on Pt

Abstract: Infrared Reflectance Absorption Spectroscopy (IRRAS) has been used to study the thermal stability of Nafion (du Pont, equivalent weight=1100) and a similar perfluorinated sulphonic acid ionomer (PFSI) made by the Dow Chemical Company (equivalent weight=560). Purified aqueous PFSI electrolytes solutions were prepared, PFSI films (0.5–5 μm) were cast from these aqueous PFSI solutions onto Pt foil substrates for spectral study after heating at various temperatures. Spectra were recorded at room temperature in a vacuum after a film on Pt had been heated at a particular temperature in the presence of air. The temperature range was 22–300°C. Spectral changes for a PFSI film on Pt were not significant when heated at up to 200°C in an air atmosphere; however, when heated at 300°C there was a significant decrease in intensity for S-O related bands indicating substantial loss of the sulphonic acid groups from these ionomers.

Planar microelectrochemical carbon monoxide sensors

Abstract: A series of planar miniaturized electrochemical CO sensors have been fabricated, each comprising three platinum electrodes (sensing, counter and reference) and a solution-cast Nafion film as a solid polymer electrolyte. The Nafion film was chosen for it compatibility with microelectronic fabrication and for its outstanding inertness. The CO sensor response characteristics were evaluated using four different substrates (smooth glass, sandblasted glass, and rougher and smoother ceramic), three different kinds of solution-cast Nafion films, and five different gap sizes (between adjacent microelectrodes) from 5 to 50 μm. The best reproducible performance was obtained from the basic planar-type CO sensor with a 10-μm gap using the smooth ceramic substrate and a 1-μm-thick Nafion 1 film. An optimal ratio of signal to background current was obtained at an applied potential of approximately − 50 mV versus the platinum/air reference electrode, at which both the background current and the CO signal became almost humidity-independent. The response is linear with the CO concentration in air, which yields an estimated sensitivity in the order of 8 pA/ppm with a typical response time in the order of 70 s. Moreover, at the − 50 mV sensing potential, the CO sensor can exclude interfering signals from NO and NO 2 and, to a large extent, interfering signals from ethanol and H 2 . However, a long-term stability test showed a drift on the sensor performance as a function of time, which was most likely due to a drift of the actual potential of the platinum/air reference electrode.

Ion‐Transporting Composite Membranes III . Selectivity and Rate of Ion Transport in Nafion‐Impregnated Gore‐Tex Membranes Prepared by a High‐Temperature Solution Casting Method

Abstract: : In a previous paper we discussed the rate of ion-transport in Nafion Impregnated Gore-Tex (NIGT) membranes. The membranes described in this previous paper were prepared by immersing the Gore-Tex in a solution of Nafion and then allowing the solvent to evaporate at room temperature. Nafion films which are cast at room temperature show poor mechanical and transport properties. This paper describes the transport properties of NIGT membranes prepared via a high temperature solution-casting method. We have found that these high temperature- cast NIGT membranes show better physical and mechanical properties than the low temperature-cast NIGT investigated previously. The two diffusion-pathway mode, described in the previous paper, quantitatively accounts for the transport data for the high temperature-cast membranes. Subject terms: Composite membranes, Nafion/Gore-Tex, Ion-transport.

Photochemical properties of PbS microcrystallites prepared in Nafion

Abstract: PbS microcrystallites ranging from 16 to 40 A were prepared in Nafion; band gaps were determined from absorption spectra. The maximal hypsochromic shift achieved by the size quantization was ca. 1.7 eV. The onset potential of anodic photocurrents at Nafion-coated electrodes with the incorporated PbS shifted cathodically with an increase in the band gap, and it satisfied the hyperbolic band theory concerning the band gap variations with the size quantization. Fluorescence of PbS microcrystallites was greatly influenced by solvents into which PbS-incorporated Nafion was immersed, as in the case of CdS-incorporated Nafion.

Effects of Surface Roughening of Nafion® on Electrode Plating, Mechanical Strength, and Cell Performances for SPE Water Electrolysis

Abstract: The most suitable conditions for surface-roughening Nafion membranes used as solid polymer electrolytes (SPE) were examined for their effect on electrode plating, mechanical strength, and cell performance for water electrolysis

Photochemical Properties of TiO2 Microcrystallites Prepared in Nafion

Abstract: TiO2 microcrystallites of different sizes were prepared in Nafion and the energy diagrams of these were determined from the onset potential of photocurrents due to oxidation of tartrate ions and the bandgap energy which was estimated from absorption spectra. The smallest particle prepared in the present study had the diameter less than 2 nm and the bandgap energy of 3.95 eV. Photocatalytic activities of the TiO2 microcrystallites prepared in Nafion for photodecomposition of acetic acid were very low compared to those of TiO2 microcrystallites prepared in clay interlayers and were comparable to those of the latter photocatalysts obtained in the presence of SO42−, suggesting that sulfonate groups of Nafion made the photocatalytic activity of TiO2 microcrystallites decrease.

Application of the SPE Method to Organic Electrochemistry-X. Behaviors of the Manganese Redox Couple Incorporated in Pt–Nafion and Their Mediatory Oxidation of Cinnamyl Alcohol to Cinnamaldehyde

Abstract: The electrochemical behavior of a manganese redox couple incorporated into an SPE (Solid Polymer Electrolyte) composite electrode using Nafion (Pt–Nafion) was examined as a mediator for electroorganic syntheses. The mediatory reaction of the redox couple was examined in the oxidation of cinnamyl alcohol. The oxidation proceeded smoothly and gave cinnamaldehyde in high selectivity; the current efficiency was as high as 85%. The dissolving-out of manganese from the SPE was suppressed by the addition of 0.025 mol dm−3 MnSO4 to the catholyte.

The electrochemistry of proteins entrapped in nafion

Abstract: The electrochemistry of cytochrome c551, cytochrome b5, and azurin at a Nafion-coated electrode is described.

Dynamic consequences of ionic permselectivity. rapid ejection from nafion coatings of anions generated electrochemically from cationic precursors

Abstract: The binuclear, cationic complex (NH 3 ) 5 Co III O 2 C-4-C 5 H 4 NRu III (edta) + (4-C 5 H 4 N=4-pyridyl) was synthesized and incorporated as a counterion in Nafion coatings on glassy carbon electrodes. Reduction of the Co(III) center of the incorporated complex causes it to dissociate into mononuclear fragments, one of which is an anionic complex of Ru II (edta). The loss of this complex from the polyanionic Nafion coating was monitored by cyclic voltammetry, and its rapid ejection was observed directly with the aid of a rotating ring-disk electrode

Perfluorinated membranes as catalyst supports

Abstract: The perfluorinated polymer Nafion and porous PTFE/Nafion composite membranes have been employed as supports for nickel complexes or for platinum and palladium metal particles. The resultant materials have been employed as catalysts in various olefin conversion processes. Supported platinum and palladium metal systems were evaluated as catalysts for the hydrogenation of cyclohexene. Rates of reaction are better than those of commercially available catalysts; turnover numbers in excess of 6000 have been obtained with no poisoning apparent. Catalysts may be regenerated many times. The reduction rate approaches a limit at high pressures of hydrogen and has an activation energy of 13 kJ mol−1 in neat cyclohexene. Nafion was employed as a strong acid cocatalyst to activate and then support a nickel complex catalyst. The resultant catalyst was active for double-bond-shift isomerization.

Modification of an ion-exchange membrane surface by plasma process. Part 3. Interfacial resistance of monovalent cation perm-selective membrane from Nafion.

Abstract: The monovalent cation perm-selectivity of Nafion® 117, perfluoro-sulfonate cation-exchange membrane, was enhanced by depositing on its surface an ultrathin anion-exchange layer prepared by plasma polymerization. The anion exchanger was deposited from a 4-vinylpyridine monomer vapor followed by quaternarization with 1-bromopropane. The resulting anion-exchange layers were found to be pinhole-free and of uniform thickness. The monovalent cation perm-selectivity of the plasmamodified Nafion membrane was determined by measuring the Fe 2+ ion transference number, tFe in a Li+–Fe2+ system. The influence of the thickness of the plasma layers on the tFe and the membrane resistance was investigated. The tFe decreased with increasing thickness of the plasma polymer layer, but at the cost of enhanced membrane resistance. The resistance of treated Nafion was separated into bulk resistance and interfacial resistance. A large interfacial resistance was observed between Nafion and the plasma polymer layer, and was ascri...