Showing papers on "Nafion published in 1994"
TL;DR: In this article, the Nafion/H[sub 3]PO[sub 4] electrolyte has been evaluated with respect to water content, ionic conductivity and transport of oxygen, and methanol vapor.
Abstract: In developing advanced fuel cells and other electrochemical reactors, it is desirable to combine the advantages of solid polymer electrolytes with the enhanced catalytic activity associated with temperatures above 100 C. This will require polymer electrolytes which retain high ionic conductivity at temperatures above the boiling point of water. One possibility is to equilibrate standard perfluorosulfonic acid polymer electrolytes such as Nafion, with a high boiling point Bronsted base such as phosphoric acid. The Nafion/H[sub 3]PO[sub 4] electrolyte has been evaluated with respect to water content, ionic conductivity and transport of oxygen, and methanol vapor. The results show that at elevated temperatures reasonably high conductivity (>0.05 [Omega][sup [minus]1] cm[sup [minus]1]) can be obtained. Methanol permeability is shown to be proportional to the methanol vapor activity and thus decreases with increasing temperature for a given partial pressure. Comparisons and distinctions between this electrolyte and pure phosphoric acid are also considered.
258 citations
153 citations
TL;DR: In this article, the impedance response of the Au/membrane/Au cell between 140 K and room temperature in the frequency range 10−2 to 106 Hz was measured for membranes aged either in air or in water after different pretreatments.
140 citations
TL;DR: In this paper, three perfluorosulfonic acid membranes (Nafion 120, Nafion 117 and Dow) were characterized by conductivity measurements in the temperature range of 20-90°C and by Small-Angle X-Ray Scattering (SAXS) at room temperature.
140 citations
TL;DR: Evidence is provided that the presence of a Nafion membrane is a solution to acetaminophen interference in glucose sensing, found to be possible by introducing a membrane constructed of Nafions.
Abstract: Amperometric glucose sensors typically monitor the production of hydrogen peroxide generated in the course of the enzymatic oxidation of glucose At the applied potential necessary to oxidize the peroxide produced, other species are also electroactive and contribute to the signal Interference of ascorbate or urate has been effectively eliminated, but that resulting from the widely used analgesic acetaminophen is not The aim of this work was to reduce this interference, which was found to be possible by introducing a membrane constructed of Nafion We compared the in vitro sensitivity to acetaminophen of five Nafion sensors with that of five non-Nafion sensors with identical glucose sensitivity (20±04 vs 19±01 nA·mmol−1· 1−1, NS): sensitivity to acetaminophen was 122±27 vs 308±63 nA·mmol−1·1−1, respectively (p<005) These sensors were tested in rats by implanting in each animal one Nafion and one non-Nafion sensors The in vivo sensitivity to glucose was similar (033±009 vs 030±005 nA·mmol−1·1−1, NS) The current generated by an acetaminophen infusion (plasma acetaminophen plateau=140±10 μmol/l) was much decreased in the case of the Nafion sensor: 05±03 vs 20±07 nA, p<005) Five Nafion sensors were implanted in the subcutaneous tissue of normal human volunteers who were given on oral dose of 500 mg acetaminophen No change in the sensor current was observed, although plasma acetaminophen reached a peak (35±6 μmol/l) at 60 min and decreased by 50% at 180 min In contrast, the current increased from 21±07 to 39±12 nA (p<005) at 60 min of a subsequent oral glucose tolerance test when plasma glucose concentration increased from 48±03 to 80±09 mmol/l This paper provides the evidence that the presence of a Nafion membrane is a solution to acetaminophen interference in glucose sensing
138 citations
TL;DR: In this article, Nafion polyelectrolyte electrodes were used for the electrocatalytic oxidation of NADH and achieved an optimal working potential of 0 to 100 mV (vs. SCE) and operation stability.
Abstract: Poly(methylene blue) (PMB)-modified electrodes show excellent properties for the electrocatalytic oxidation of NADH concerning the optimal working potential of 0 to 100 mV (vs. SCE)and their operation stability. By means of dehydrogenases entrapped within a Nafion film on top of the PMB layer, new amperometric biosensors for glucose, lactate, malate, and ethanol could be obtained with improved integration of the enzyme and the electrocatalyst directly on the electrode surface. Coentrapment of the negatively charged NAD+ within the negatively charged Nafion Polyelectrolyte leads to reagentless dehydrogenase electrodes for one-shot or short-term applications.
136 citations
TL;DR: Curing at 120 degrees C can be used to improve the in vivo durability of a miniaturized glucose sensor with an outer coating of the Dupont perfluorinated ionomer, Nafion, and several of the fully assembled, heat-cured, needle-type glucose sensors remained functional for at least 10 days after subcutaneous implantation in dogs.
Abstract: In this paper we report that curing at 120 degrees C can be used to improve the in vivo durability of a miniaturized glucose sensor with an outer coating of the Dupont perfluorinated ionomer, Nafion. Sensors based on glucose oxidase trapped in an albumin/glutaraldehyde matrix were able to withstand curing at 120 degrees C without noticeable change in electrode sensitivity (+/- 22% SD). Curing above 120 degrees C caused a gradual decline in sensitivity, with no sensitivity seen at 170 degrees C. Curing Nafion at 120 degrees C eliminated ascorbic acid and urea interferences and improved selectivity for glucose against uric acid and acetaminophen, compared to room temperature-cured Nafion coatings. The Nafion film reduced O2 demand by the sensor, so the signal was O2 independent across a partial pressure range of 8-140 mmHg. Several of the fully assembled, heat-cured, needle-type glucose sensors remained functional for at least 10 days after subcutaneous implantation in dogs, without degradation of their sensitivity (average 3 nA/mM in vivo at 37 degrees C and 6 nA/mM in vitro at 37 degrees C).
122 citations
TL;DR: In this article, a molecular-level equilibrium partition coefficient model has been formulated to describe single and multicomponent ion uptake by a Nafion 117 cation exchange membrane, which assumes a cylindrical pore structure for the membrane and considers ion solvation free energy changes which occur during solute partitioning and the orientation of solvent dipoles inside a membrane pore due to the strong electric field generated by the membrane's fixed-charge groups.
108 citations
TL;DR: It is demonstrated that if unprotected, the AgCI layer of the reference electrode rapidly dissolves in the biological environment, however, it is later showed that in vivo degradation of Nation can be prevented by heat curing.
Abstract: We have developed an implantable glucose sensor based on a new tri-layer membrane configuration. The needle-type sensor integrates a Pt working electrode and a Ag/AgCl reference electrode. Its size is equivalent to a 25 gauge needle (0.5 mm in diamater). Poly (o-phenylenediamine) was used as an inner coating to reduce interference by small compounds present in the body fluids, and the perfluorinated ionomer, Nafion as a biocompatible, protective, outer coating. Glucose oxidase trapped in an albumin/glutaraldehyde matrix was sandwiched between these coatings. In vitro tests in buffer showed the sensors had a good selectively, a sensitivity of about 25 nA/mM, and a 90% response time of 33 s. Stabilization of the current following polarization required 10 to 30 min in vitro and 30 to 40 in vivo. Although these sensors remained stable for many weeks in saline solution, their implantation in animals resulted in the degradation of the protective Nafion outer coating, which in turn, led to the failure of the incorporated reference electrode. We demonstrated that if unprotected, the AgCl layer of the reference electrode rapidly dissolves in the biological environment. However, we later showed that in vivo degradation of Nafion can be prevented by heat curing. When heat cured sensors were subcutaneously implanted in dogs, the sensors' signal closely followed the plasma glucose level during glucose tolerance tests. The response of the sensors implanted in dogs was retained for 10 days.
94 citations
TL;DR: In this article, the progress in developing electrocatalyst systems and electrode structures primarily for the positive electrode of single-unit solid polymer proton-exchange membrane (PEM) regenerative fuel cells was updated.
83 citations
TL;DR: Matrix-assisted laser desorption/ionization using a 3-hydroxypicolinic acid matrix from an active Nafion substrate has been used for detection of restriction enzyme-digested double-stranded plasmid DNA using time-of-flight mass spectrometry.
Abstract: Matrix-assisted laser desorption/ionization using a 3-hydroxpicollinic acid matrix from an active Nafion substrate has been used for detection of restriction enzyme-degested double-stranded plasmid DNA using time-of- flight mass spectrometry. DNA strands of up to 267 base pairs were detected with minimal sample purification, although only as species corresponding to single-stranded DNA.
TL;DR: In this paper, the Dow experimental PEM (XUS-13204.10) and unsupported high platinum loading electrodes yielded very high power densities, of the order of 2.5 W cm(exp -2).
TL;DR: In this paper, the fabrication and surface morphology of methylene blue (MB)/perfluorosulfonated ionomer (Nafion) modified microcylinder carbon fiber electrode were studied.
Abstract: The fabrication and surface morphology of methylene blue (MB)/perfluorosulfonated ionomer (Nafion) modified microcylinder carbon fiber electrode were studied. The stability of the modified electrode is good. The extraction coefficient K of MB between Nafion film and solution is ∼110, and the diffusion coefficient of MB in Nafion film is ∼5.3×10 -9 cm 2 /s. The MB/Nafion modified microcylinder electrode shows significant electrocatalytic activity for the oxidation of hemoglobin in weak acid media; it can be used for the determination of hemoglobin in the range of 5.0-50 μM with a relative standard deviation of 3.5% at 6.0 μM HB
TL;DR: In this paper, a rotating disk electrode (RDE) was used as a binder to hold the carbon-supported electrocatalyst on the disk electrode, and the results obtained with the RDE in an oxygen-saturated SO{sub 4} solution mimic those measured for a full-cell H{sub 2}/O{sub 3} solid polymer electrolyte setup.
Abstract: Carbon supported electrocatalysts for the reduction of oxygen can be screened quickly by using a rotating disk electrode (RDE) when an appropriate material is used as a binder to hold the catalyst on the disk electrode. The results obtained with the RDE in an oxygen-saturated H{sub 2}SO{sub 4} solution mimic those measured for a full-cell H{sub 2}/O{sub 2} solid polymer electrolyte setup. This result is demonstrated with a cobalt phthalocyanine-on-carbon black catalyst pyrolyzed at various temperatures ranging from 400 to 1,100 C. When the catalyst is held on the disk electrode with electropolymerized pyrrole, a broad maximum of activity for the reduction of oxygen is observed for pyrolysis temperatures ranging between 600 and 900 C. When the catalyst is dispersed in a Nafion film on the disk electrode, a sharp maximum in its activity is observed at the pyrolysis temperature of 600 C, in agreement with its behavior in a full-cell setup.
TL;DR: In this paper, a highly selective electrochemical detection of dopamine using an interdigitated microarray (IDA) electrode coated with Nafion and polyester ionomer (Kodak AQ29D) layered films is presented.
Abstract: The highly selective electrochemical detection of dopamine has been developed using an interdigitated microarray (IDA) electrode coated with Nafion and polyester ionomer (Kodak AQ29D) layered films. Because high redox cycling of dopamine can be maintained in the AQ29D bottom layer, a low detection limit of 50 nmol/dm3 is obtained. Since the upper Nafion laybr prevents L-ascorbic acid from diffusing into the AQ29D layer, the acid concentration in this layer rapidly decreases when potentiostating one IDA electrode (anode) above and the other (cathode) below the redox potential of dopamine. This is because L-ascorbic acid molecules in the AQ29D layer are removed quickly by the electrochemical or electrocatalytic oxidation at the anode. On the other hand, almost all of the oxidized dopamine molecules are reduced at the cathode, which maintains a constant dopamine concentration in the film during measurement. After the potential step, the influence of L-ascorbic acid is almost completely eliminated within a few seconds due to the reduction in acid concentration in the modified layer. As a result, dopamine can be detected quantitatively at the cathode in the presence of 100-fold excess of L-ascorbic acid.
TL;DR: In this article, the transport mechanisms of water and uncharged solute molecules (PEG) through two new nanofiltration membranes: a pure ceramic (γ-alumina) and a Nafion layer deposited on a mesoporous tita-nium oxide substrate.
TL;DR: The use of an active Nafion substrate is shown to enhance the performance of MALDI MS and to be particularly effective in analyzing real biological mixtures without prepurification.
Abstract: The use of an active Nafion substrate is shown to enhance the performance of MALDI MS. The use of a Nafion substrate with certain matrices can significantly enhance the signals obtained over those observed with a stainless steel probe substrate. Analytes can often be observed with the use of the Nafion substrate that cannot be easily observed with the standard MALDI procedure, and usually a much wider range of peaks can be observed using MALDI from the Nafion substrate than with any single matrix on a stainless steel substrate. This enhancement of signal from the Nafion substrate is observed only with the sequential deposition of the sample and the matrix onto the Nafion film. If the analyte and matrix are premixed, then the effect is not observed. The use of the Nafion substrate has been shown to be particularly effective in analyzing real biological mixtures without prepurification. This has been demonstrated for various samples including the analysis of the products of chemical digests of proteins, protein profiling in milk and egg white samples, cell lysate analysis, and oligonucleotide detection.
TL;DR: In this paper, the surface morphology of dry and swollen Nafion films was investigated on the micrometer and nanometer scale by scanning force microscopy, and the results showed that the disordered network structure of dry films undergoes a reorganization process in the course of swelling and transforms into an ordered structure of parallel fibrils.
Abstract: The surface morphology of dry and swollen Nafion films was investigated on the micrometer and nanometer scale by scanning force microscopy. The results show that the disordered network structure of dry films undergoes a reorganization process in the course of swelling and transforms into an ordered structure of parallel fibrils. No substantial changes in the fibril dimensions were found in the swollen state. This can be an indicator that swelling occurs at the supramolecular level.
TL;DR: In this paper, an electrochemical study of three important β-agonist drugs at unmodified and Nafion-modified carbon paste electrodes was carried out, where the modification of the carbon paste surface with a nafion film allowed a preconcentration process to take place, such that higher sensitivities were achieved compared with the bare surface.
Abstract: An electrochemical study of three important β-agonist drugs at unmodified and Nafion-modified carbon paste electrodes was carried out. All the compounds are oxidized irreversibly at high positive potentials at a bare carbon paste electrode, giving rise to sharp, well-defined peaks. A secondary oxidation process was observed at pH values above 6.0. The rate-determining step was investigated for each compound at two concentration levels. Electrochemical activation procedures were optimized to ensure reproducible signals for the construction of calibration graphs. The modification of the carbon paste surface with a Nafion film allowed a preconcentration process to take place for all compounds, such that higher sensitivities were achieved compared with the bare surface. Such modifications resulted in limits of detection for the compounds down to 2.5 × 10–8 mol dm–3. Optimum accumulation was obtained at low pH values (2–3). Cyclic voltammetry at two Nafion film thicknesses demonstrated that a diffusion-controlled process exists within the Nafion layer. Salbutamol showed a higher affinity for Nafion than the other two compounds, both in terms of longer linear accumulation and linear accumulation at higher concentrations.
TL;DR: In this paper, a glucose-sensitive electrode composed of glucose oxidase (GOX) embedded in a layer of the polymer Nafion is described, and the electrodes are tested to determine their response to glucose additions to phosphate buffer and human whole serum samples.
Abstract: A glucose-sensitive electrode composed of glucose oxidase (GOX) embedded in a layer of the polymer Nafion is described. Electrodes of various configurations on which the layer was cast were tested to determine their response to glucose additions to phosphate buffer and human whole serum samples. These electrodes have good response characteristics and several desirable features. Glucose sensors based on Nafion/GOX layers cast onto platinum electrodes respond to glucose additions with a rapid response time (2 to 4 seconds), have a long lifetime when stored in a phosphate buffer (55 days before termination of testing), have a reduced sensitivity to local oxygen tension, respond linearly to additions of glucose to the serum, and are not fouled by exposure to blood. The Nafion confers some permselectivity on the layer, thus providing a degree of discrimination against anionic interferents.
TL;DR: A carbon electrode coated with lipoamide dehydrogenase and methyl viologen under a Nafion® film provides the basis for a convenient system for electrochemical regeneration of NADH.
TL;DR: In this article, the authors measured the dc conductivity of the solution-cast PFSI membranes from perfluorosulfonated ionomers (PFSI) and their blends from E. I. du Pont de Nemours and Dow Chemical's XUS.
Abstract: Solution-cast membranes from perfluorosulfonated ionomers (PFSI) and their blends were prepared from E. I. du Pont de Nemours's Nafion 117 and Dow Chemical's experimental membrane XUS. Water sorption and ac impedance measurements were performed on the solution-cast membranes in an attempt to characterize their electrical properties. Water uptake versus relative humidity for the solution-cast membranes was measured and it was observed that the solution-cast membranes imbibe less water than as-received membranes. The dc conductivity was extracted from the impedance measurements, and the room temperature dc conductivity of the solution-cast membranes was found to be approximately 10 -7 -10 -6 S/cm, ≃10 4 times lower than the room temperature conductivity of the original PFSI membranes
TL;DR: In this paper, the electric potential distribution across a Nafion® membrane during water electrolysis using a solid polymer electrolyte has been computed and the use of a membrane strip to measure separately the anodic and cathodic overvoltages is discussed.
TL;DR: Perfluorosulfonate ionomer membranes (Nafion) that have been ion-exchanged with silver(I) ion exhibit unexpectedly large selectivities for the separation of certain unsaturated hydrocarbon mixtures, such as styrene from ethylbenzene and linear C[sub 5]-C[sub 10] dienes from monoenes.
Abstract: Perfluorosulfonate ionomer membranes (Nafion) that have been ion-exchanged with silver(I) ion exhibit unexpectedly large selectivities for the separation of certain unsaturated hydrocarbon mixtures, such as styrene from ethylbenzene and linear C[sub 5]-C[sub 10] dienes from monoenes. Transmembrane fluxes increase linearly with the reciprocal of membrane thickness with no loss of selectivity for membrane thicknesses between 40 and 2.5 [mu]m. The large selectivities are due to competitive absorption of the hydrocarbons by the membranes. This effect cannot be predicted from single-component experiments or known complexation constants between the hydrocarbon and aqueous Ag(I). The unexpectedly large separation factors for the diene/monoene mixtures can be explained semiquantitatively by invoking the complexation of dienes to two Ag(I) ions. 44 refs., 9 figs., 7 tabs.
TL;DR: In this article, a Nafion® / ruthenium-oxide pyrochlore (Pb2Ru2-xPbxO7-y) chemically modified electrode (CME) was constructed for the determination of dissolved oxygen (DO).
TL;DR: In this article, Nafion membranes containing immobilized FeIII tetrakis(N-methyl-4-pyridyl)porphyrin showed spectroscopic changes in the UV-VIS range after exposure to gaseous NO, indicating the formation of a nitrosyl complex.
Abstract: Nafion membranes containing immobilized FeIII tetrakis(N-methyl-4-pyridyl)porphyrin show spectroscopic changes in the UV–VIS range after exposure to gaseous NO, indicating the formation of a nitrosyl complex; electroreduction of NO is mediated by this metalloporphyrin when immobilized in Nafion-coated glassy-carbon electrodes and the use of these film electrodes for the amperometric determination of NO in aqueous solutions is demonstrated.
TL;DR: The signal stability of the Nafion-coated thin mercury film electrode (NCTMFE) was studied by using cadmium and lead as test analytes and differential pulse anodic stripping voltammetry as detection method.
TL;DR: In this paper, small-and wide-angle X-ray scattering (SAXS) and WAXS were used to characterize room temperature recast Nafion1 films, prepared under different humidities in the curing atmosphere.
Abstract: Room temperature recast Nafion1 films, prepared under different humidities in the curing atmosphere, were characterized by small- and wide-angle X-ray scattering (SAXS and WAXS). SAXS reveals that the humidity influences the size of the ionic clusters in these polymer films. It was found that the number and size of ionic clusters increases with increasing relative humidity. WAXS indicates the presence of locally ordered regions of the backbone polymer. These results allow a qualitative understanding of the electrochemical behaviour of Nafion recast films cured at different humidities, as described in the literature.
TL;DR: Chemically facilitated Donnan dialysis of heavy metal ions in combination with continuous reagent flow has been studied and a simplified model to describe this process has been established.
Abstract: Chemically facilitated Donnan dialysis (CFDD) of heavy metal ions in combination with continuous reagent flow has been studied. A simplified model to describe this process has been established. The model relates the diffusion behavior of metal ions through a Nafion cation-exchange membrane with the stability constant of complexation, the ionic strength of the receiving and sample solutions, the flow rate of the receiving solution, and the area-to-volume ratio of the membrane dialysis cell. A novel fiber optic heavy metal sensor has been fabricated by directly interfacing the dialysis device with a fiber optic colorimetric detection mechanism