Showing papers on "Nafion published in 1988"

Methods to Advance Technology of Proton Exchange Membrane Fuel Cells

Abstract: Proton exchange membrane (PEM) fuel cells showing promise of a high level of performance have, up to the present time, used electrodes containing a high platinum loading (4 mg/cm2). We report improvements in performance of PEM fuel cells utilizing electrodes with only one‐tenth of this platinum loading by (i) extension of the three‐dimensional reaction zone by incorporation of a proton conductor (Nafion) into the electrode structure; (ii) optimization of the amount of Nafion impregnated into the electrode structure; (iii) hot‐pressing the impregnated electrodes to the Nafion membrane at 120°C and 50 atm; (iv) optimal humidification of reactant gases at a temperature above that of the cell (5°C for or air and 10°–15°C for ); and (v) operation at elevated temperatures and pressures. The performance of the cells was analyzed from measurements of cell potential vs. current density and of cell potential at constant current density vs. time. Cyclic voltammetry proved to be a useful tool to ascertain the electrochemically active area of the electrodes.

Oxygen Reduction at Nafion Film‐Coated Platinum Electrodes: Transport and Kinetics

Abstract: The primary objectives of the work described in this paper were to evaluate the concentration and diffusion coefficient of in a commercial perfluorosulfonate ionomer (Nafion) and to assess the effect of a film of this ionomer on the rate of reduction at a substrate Pt electrode surface. Electrochemical experiments at Nafion film‐coated electrodes were used to obtain these data. A high temperature film‐casting procedure, which has been shown to yield high quality solution‐cast Nafion films, was used to prepare the Nafion‐coated electrodes. The Nafion film‐coated electrodes were equilibrated with and exposed to during the electrochemical experiments; it was of particular interest to compare the diffusion, solubility, and kinetic data obtained at the film‐coated electrode to analogous data obtained at a bare electrode, exposed to this electrolyte. We have found that the diffusion coefficient is lower in Nafion than in the electrolyte solution but that the solubility and oxygen reduction rate are higher.

The electrochemical reduction of CO2 to CH4 and C2H4 at Cu/Nafion electrodes (solid polymer electrolyte structures)

Abstract: The construction of copper/Nafion electrodes (solid polymer electrolyte structures) by an electroless plating method is described. These electrodes were used for the gas phase electrochemical reduction of CO2 to hydrocarbon products, including CH4 and C2H4. The faradaic efficiencies of the electrodes under ambient conditions with a counter solution of 1 mM H2SO4 at a potential of −2.00 V vs. SCE reached a steady-state value of about 20% after 30 min of electrolysis. This corresponded to a rate of total hydrocarbon production of approximately 9.8×10−7 mole h−1 cm−2. Increasing the potential of the electrode to more negative potentials, or increasing the proton concentration of the counter solution, caused a decrease in the faradaic efficiencies due to a relative increase in the rate of proton reduction vs. that of CO2 reduction. If the proton concentration of the counter solution was decreased to an alkaline pH, hydrocarbon production quickly ceased because of proton starvation.

Studies on the thermal stability of the perfluorinated cation-exchange membrane Nafion-417

Abstract: The thermal stability of the perfluorinated cationexchange membrane Nafion-417 was determined by means of simultaneous TG-DTA. The individual decomposition stages were studied via IR spectroscopy and ion-exchange capacity determinations. Nafion-417 is thermally stable up to 280 ‡C. Above this temperature, sulfonic groups present in the membrane are split off (Tmax= 345 ‡C. In the temperature range 420–590 ‡C, oxidative destruction of the perfluorinated matrix occurs, which is accompanied by practically total weight loss.

Electrochemical Behaviors of Polypyrrole, Poly‐3‐methylthiophene, and Polyaniline Deposited on Nafion‐Coated Electrodes

Abstract: Anodic polymerization of pyrrole, 3‐methylthiophene, and aniline at Nafion‐coated electrodes gives conducting polymer‐Nafion composite films The composite films show better reversibility in the film redox process than conducting polymer films alone, owing to different charge compensation mechanisms in the redox reaction; electrolyte cations are involved in the redox process of the composite films, whereas electrolyte anions are in the ordinary conducting polymers The fast kinetics of the redox process of the composite films are effectively demonstrated by an improvement of the polypyrrole electrochromic response and by the efficient utilization of stored charge by the composite film electrodes

Electrooxidation of methanol on platinum bonded to the solid polymer electrolyte, Nafion

Abstract: The electrooxidation of methanol was enhanced on PtSn-SPE, PtRu-SPE and PtIr-SPE in sulfuric acid solution, when compared with the activity of Pt-SPE, which has already been shown to have a higher activity than a Pt electrode. SPE is an abbreviation for Nafion, a solid polymer electrolyte. It is suggested that this dual enhancement of the oxidation rate for PtSn-SPE and PtRu-SPE catalysts is due to the modification of the oxidation state of Pt by Sn and Ru and to the presence of H2O and CH3OH, both modified by the SPE matrix. This modification appears to weaken their hydrogen bonds in solution. Both Pt and Ir have catalytic properties for methanol oxidation, but a PtIr-SPE catalyst showed a more enhanced catalytic activity than either of them. This will be discussed in terms of Ir, oxidized at relatively low positive potentials, assisting the redox process of Pt0/Pt2+ or Pt2+/Pt4+ in the SPE matrix, where CH3OH and H2O are present in modified forms. For comparison, IrPd-SPE was also used as an electrode and showed a higher activity than Ir alone, although Pd did not have any activity toward methanol oxidation in sulfuric acid solution. Irrespective of the kind of Pt-SPEs, the Tafel slope was approximately 120 mV; the CH3OH concentration dependence was of the order of 0.2–0.6. The pH dependence was nearly 0.5 against NHE. The activation energy of the Pt-SPEs for the reaction ranged between 20 and 33 kJ mol−1.

Conductive polymers with immobilised dopants: ionomer composites and auto-doped polymers-a review and recent advances

Abstract: The electrodeposition of poly(pyrrole) in the presence of a polyanionic electrolyte (poly(styrenesulphonate), poly(vinylsulphate) or Nafion) leads to the formation of a film of a composite polymer at the surface of the two polymeric structures prevents the anionic dopants from being expelled during the dedoping, consequently cations are inserted. This cation-exchange behaviour is the origin of applications in the field of charge-controllable membranes such as water deionisation and the polymer battery, reported by Shimidzu and co-workers (1987). The immobilisation of the anionic dopant has also been achieved by their direct covalent binding to the conductive polymer backbone, leading to the concept of internal doping or 'auto-doping'. The poly(3-alkylsulphonate-thiophenes) (1987) reported by Wudl, Heeger and co-workers (187) are revealed to be the first water-soluble conductive polymers. A study of the poly(3-methylpyrrole-4-carboxylic acid) by Pickup (1987) shows that the formal potential of this polymer is sensitive to pH. The copoly(pyrrole+N-alkylsulphonate-pyrrole) presented by the authors in more detail exhibits a remarkable mixed behaviour as a result of the coupling of cationic membrane with conductive polymer properties. In particular, the electrochemical behaviour of this co-polymer is very sensitive to the water content of the solvent.

Application of Nafion/Platinum Electrodes (Solid Polymer Electrolyte Structures) to Voltammetric Investigations of Highly Resistive Solutions

Abstract: Platinum electrodes on Nation~ 115 membranes, designated Pt/Naf and prepared by an electroless plating method (PtC162- with hydrazine), were used for voltammetric investigations. Scanning electron microscopy (SEM) of these electrodes showed the Pt electrode surface to have the continuous, yet porous, structure necessary for both electronic conduction to the Pt particles and ionic conduction through the membrane/electrode/solution interface. These electrodes were used in the configuration S/Pt/Naf/H20 + electrolyte, where the counter and reference electrodes were in the aqueous electrolyte solution and the substance of interest was dissolved in solvent, S. Cyclic voltammetry was used to characterize the behavior of several substrates in H20, MeCN, THF, and toluene. Tetracyanoquinod imethane (TCNQ) in acetonitrile (MeCN), tetrahydrofuran (THF), and toluene and benzoquinone (BQ) in THF and toluene could be reduced to anion radicals in the absence of added supporting electrolyte. In THF and toluene, the formation of the radical anion of BQ and TCNQ often involved ion pair formation with alkali metal ion and precipitation. The reduction of TCNQ in toluene in the presence of Na § ions resulted in the formation of the electronically conducting salts, Na+TCNQ -. This paper describes the construction of Pt electrodes, based on solid polymer electrolyte (SPE) technology, that can be employed for voltammetric measurements and their application to studies with several solvent systems, including some very resistive ones that contain no or low amounts of added supporting electrolyte. SPE techniques involve the use of an ion exchange membrane (usually Nation 1) with porous contacting electrodes for the construction of electrochemical devices in which ionic migration to maintain charge neutrality occurs within the membrane. SPE technology was first applied to fuel cells (1) and later to water electrolyzers (2) and electrochemical oxygen separators (3). Our goal was to utilize these SPE electrodes in a voltammetric mode to help establish appropriate conditions for bulk electrolysis and for analysis. In this way such SPE electrodes could be used to complement ultramicroelectrodes (4, 5) in the electrochemical characterization of systems in resistive media. We also were interested in obtaining a better understanding of the operation and structure of the voltammetric SPE electrode.

Membrel‐Water Electrolysis Cells with a Fluorinated Cation Exchange Membrane

Abstract: Stability tests demonstrate the possibility of using a low cost fluorinated cation exchange membrane for water electrolysis cells under conditions necessary to obtain cell voltages of economical interest (80 °C, 1 A/cm2).

Enhanced oxygen evolution through electrochemical water oxidation mediated by polynuclear complexes embedded in a polymer film

Abstract: Oxygen evolution by electrochemical water oxidation has been studied. The reaction was carried out through electrochemical water oxidation mediated by polynuclear complexes embedded in a Nafion film. The polynuclear complexes used were the µ-oxo-trinuclear ruthenium complex, [(NH3)5 RuORu(NH3)4ORu(NH3)5]Cl6 and [graphic omitted]. These complexes are effective as mediators for enhanced oxygen evolution. The mediated water oxidation has been demonstrated by potential vs. current characteristics and by oxygen analysis by gas chromatography.

Process for the preparation of a mixed ionically and electronically conductive polymer, and polymers obtained by this process

Abstract: Preparation of a mixed ionically and electronically conductive polymer. An electronically conductive polymer 13, for example polypyrrole, polyaniline or polythiophene is formed by electropolymerisation in a rigid hydrophobic gel layer 9 of an ionically conductive ionomer such as Nafion. The gel layer initially contains the base monomer of the electronically conductive polymer, for example pyrrole, aniline or thiophene. An electrolyte can be introduced in the form of an aqueous solution 11 above the gel layer, or may be incorporated into the gel layer 9. It is also possible to include a membrane of ionomer, for example of Nafion, in the gel layer, to form the electronically conductive polymer within the thickness of this membrane.

A Solid-State Amperometric Oxygen Sensor Using NAFION Membrane Operative at Room Temperature

Abstract: New type amperometric oxygen sensors using a NAFION membrane were investigated for monitoring oxygen partial pressure at room temperature. The sensor element finally constructed had a structure in which an electrochemical cell was combined with a hydrogen-generation system and a gas-diffusion layer. Its sensing current under the short-circuit condition was found to vary linearly with the oxygen partial pressure. The 90% response time was about 3 min at 25 °C.

Cell responses to biomaterials. II: Endothelial cell adhesion and growth on perfluorosulfonic acid.

Abstract: We report here the use of perfluorosulfonic acid (Nafion) as a substratum for the growth of bovine aortal endothelial cells. This support which can be generated in a number of forms is at least as efficient in maintaining the growth of endothelial and other cell types as tissue culture grade polystyrene (TCP) and represents an advance in this regard over polytetrafluoroethylene (Teflon). The mechanism underlying the different cell attachment capacities of these three polymers is not readily related to their different protein binding patterns. While Nafion adsorbs more total protein from serum than Teflon or TCP, it adsorbs relatively less of the major cell adhesive proteins, vitronectin and fibronectin, than does Teflon. Both Nafion and Teflon had comparable but low thrombogenic potential by in vitro tests. Teflon or expanded Teflon (Gore-tex) coated with a thin film of Nafion assumes the cell supportive characteristics of Nafion and hence the modification of these surfaces by the induction of a stable bond between Teflon (in various forms) and Nafion may provide a composite vascular graft material which has all the desirable qualities of both materials.

Composite polymers of polyaniline with metal phthalocyanine and polyaniline with organic sulfonic acid and nafion

Abstract: The present invention relates to a process for the production of an electrochromic electrically conductive composite membrane, which process comprises: (a) combining aniline and metal phthalocyanine in dilute hydrochloric acid; and (b) applying to the solution of step (a) a constant current density of between about 0.05 and 0.2 milliamperes/cm 2 for between about 1 to 10 minutes on an electrode selected from a transparent platinum electrode or an ITO electrode to produce the improved electrically conductive electrochromic membrane. The present invention also relates to a process for the production of an electrically conductive composite membrane which comprises: (a) combining aniline, organic sulfonic acid and NAFION® all in the acid form and electropolymerizing the aqueous solution to obtain the polyaniline thin film. The electrochromic electrically conductive composite membrane produced by the process is described which is colorless when subjected to between about -0.3 V to 0 V and green to blue when subjected to between 0 V and +0.6 V. These films are useful in electrochromic displays.

The Electrochemical Behaviour of Iron(II/III) on NAFION Coated Electrodes

Abstract: The redox-system Fe2+/3+ in aqueous H2SO4 electrolytes was investigated with platinum electrodes coated with a perfluorosulfonate polymer (“Nafion”). The partitioning of the redox ions into the membrane-type coating can be described by a classical ion-exchange mechanism involving largely electrostatic forces. The apparent heterogeneous charge-transfer standard rate constant was determined by a transient impedance technique in 0.05 to 0.5 M H2SO4 to be of the order of k0′ ≈ 1 · 10−3 cm s−1. At the lower H2SO4 concentrations the analysis of the charge-transfer kinetics was not conducted because in this case the redox-ion transport does not proceed by a simple diffusion mechanism. The diffusion coefficients of the redox ions in the membrane are of the order of 10−7 cm2 s−1. The known phase-separation phenomena of the considered polymer are not noticeable in the electrochemical behaviour of the coated electrodes in this electrolyte.