Showing papers on "Nafion published in 1985"

Gas Permeation Properties of Solid Polymer Electrolyte (SPE) Membranes

Abstract: Gas permeation properties for Nafion membranes and their composites were investigated under various conditions. The permeability coefficients of Nafion depended greatly on the water content, the cation form, and the ion‐exchange capacity. The gas permeation rate through a same sample varied with temperature, pressure, and membrane thickness. The permeabilty of hydrogen was about twice as great as that of oxygen. The electrocatalyst plated on the membrane did not serve as a barrier for gas permeation, but the structure of the catalyst layer played an important role in gas permeation during water electrolysis.

Ion Transporting Composite Membranes I . Nafion‐Impregnated Gore‐Tex

Abstract: : Ion transporting membranes are required in a variety of electrochemical processes and devices including chlorine-caustic production, batteries, fuel cell, electrolyzers, etc. Nafion, a perfluorosulfonate ionomer marketed by Du Pont has proved useful for a number of these applications. Nafion has a number of attractive features including good chemical and mechanical stability and high perselectivity. In addition, however, it has two potentially significant disadvantages - it is a cation transporting membrane (i.e., there is no anion transporting equivalent) and it is rather expensive. These difficulties have prompted efforts to develop anion and cation transporting materials which have Nafion's desirable chemical and mechanical features but which can be produced more cheaply. It occurred to us that a cheaper and more versatile membrane material might be prepared by doping an inexpensive, nonconductive material with a small amount of an ion transporting polymer. In an effort to demonstrate the feasibility of this approach, we have impregnated commericially available porous polytetrafluoroethylene membranes (Gore-Tex) with small quantities of Nafion, to make cation transporting composites. Electrode surfaces were covered with these composite membranes electrochemical techniques were used to study the membranes transport properties. We have shown that the Nafion-doped Gore-Tex does, indeed, transport cations and that the rate of transport can be much higher than the transport rate in a pure Nafion membrane. Keywords include: Ionic conduction, Membranes, Transport.

Voltammetric Studies of Electrodes in Contact with Ionomeric Membranes

Abstract: Cyclic voltammetry studies were carried out on platinum and gold screen electrodes in contact with Nafion ionomeric membranes. In addition, experiments were carried out on multiple combinations of platinum screens with either graphite felt or gold screen electrodes, with only one of the electrodes in direct contact with th membrane. In the case of platinum and gold screens, it was found that the voltammograms were almost identical to that found for the same screens in acidic aqueous electrolytes. When two platinum screens were used, the adsorption charge on the platinum doubled. Obviously, adsorption can occur on sites remote from the membrane/electrode contact, provided the metal is wetted with water. In the case of platinum, a mechanism based on rapid mobility of absorbed hydrogen and hydroxyl species is proposed. The implications of these findings regarding solid polymer electrolyte electrolyzers and fuel cells are discussed.

Luminescence Probe Studies of Ionomers. I. Steady-State Measurements from Nafion Membrane.

Abstract: : Steady state luminescence probe methods were used to study the polarity of the ionic cluster phase within Nafion 117 membrane Three probes, pyrene, a cationic dansyl derivative and Ru(bpy)3(2+) were used In fully hydrated Nafion membranes (ca 40% water by weight), these probes report back microenvironment polarities significantly lower than bulk water In addition, these probes show that the -SO3H sites are chemically heterogeneous The effects of water content and counterion on cluster phase polarity were also evaluated The cluster phase can become quite nonpolar when water is removed and/or when a hydrophobic counterion is added The effects of the Nafion chemical environment on the dynamics and thermodynamics of chemical processes occurring within the polymer are discussed and demonstrated Originator supplied keywords include: Ion exchange membranes; Luminescence probe studies; Nafion

Surface analysis of semiconductor-incorporated polymer systems. 1. Nafion and cadmium sulfide-Nafion

Abstract: The Journal of Physical Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Surface analysis of semiconductor-incorporated polymer systems. 1. Nafion and cadmium sulfide-Nafion N. Kakuta, J. M. White, A. Campion, A. J. Bard, M. A. Fox, and S. E. Webber J. Phys. Chem., 1985, 89 (1), 48-52• DOI: 10.1021/j100247a014 • Publication Date (Web): 01 May 2002 Downloaded from http://pubs.acs.org on February 12, 2009

Integrated chemical systems: photocatalysis at titanium dioxide incorporated into Nafion and clay

Abstract: Activite catalytique des deux systemes dans la reduction du N,N'-dimethylbipyridylium-4,4' avec oxydation de la triethanolamine Mecanisme

Percolation conductivity in Nafion membranes

Abstract: This article deals with the method of determination of a threshold volume fraction of the conductive phase within perfluorosulfonic acid ionomer Nafion. Experiments have been performed with the commercial Nafion-120 and Nafion-427 membranes equilibrated with concentrated sodium chloride and sodium hydroxide solutions at 353 K. It has been stated that the insulator-to-conductor transition in membranes occurs at the critical volume fraction of the conductive phase (Vc) equal to 0.1. The same Vc has been estimated for a geometrical cluster-network model. Lower than the theoretical Vc for a classical dense-packed-hard-sphere model (Vc = 0.15), the volume fraction for the membranes is caused mainly by channels connecting the ionic clusters. The critical exponent t has been calculated for both membranes and found to be equal to 1.6 for Nafion-120 and 1.5 for Nafion-427. Both these constants correspond to those theoretically predicted for 3D systems. The ratios of sodium ion mobility in the internal membrane solution to its mobility in the equilibrating NaCl or NaOH solutions (u+/u+) are below unity, and they are dependent on the nature and concentration of the electrolyte.

Ion penetration through tubular ion exchange membranes.

Abstract: Etude sur du polytetrafluoroethylene, polyacetate d'ethyl vinyle et polyperfluorosulfonate. Influence de la taille et de la charge de l'ion

The Influence of Supporting Electrolyte on Kinetics of Electroreduction Process of Poly(methylviologen), Poly(methylviologen)‐Nafion Complex, and Poly(methylviologen)‐Poly(p‐styrenesulfonate) Complex Coated on Electrodes

Abstract: Revetement d'une electrode de graphite pyrolytique par ces polymeres. Comparaison entre les differents composes du titre

Permeation of vanadium cations through anionic and cationic membranes

Abstract: The permeability of four commercially available ion-exchange membranes, the cationic Nafion 125 (duPont) and Selemion CMV (Asahi Glass) membranes and the anionic Selemion AMV and DMV membranes, to vanadyl, VO2+, and vanadic, VO 2 + , ions was studied. The results show that two important variables determine the usefulness of a membrane as a membrane separator in a redox cell. These are selectivity and membrane-electrolyte resistance. Only the DMV membrane was considered to meet the requirements of low permeability to vanadium cations and at the same time permitting H+ ions to go through the membrane, thereby providing a very low membrane-electrolyte resistance in the redox fuel cell.

Fundamentals and Applications of Ion Exchange

Abstract: Ion Exchange Towards the Twenty First Century.- The Use of Some Coordinating Copolymers in Hydrometallurgy.- The CCS-Ion Exchange Contactor.- Outlook and Desires of Ion Exchange Resin Technology Development in the Nuclear Field.- Purification of Effluents of Acid Copper and Nickel Plating Galvanic Processes with Conventional Cation Exchange Resins. Copper and Nickel Recovery.- Anion Resin Kinetics at High Flow Rates.- Ion Exchange Desulphation of Feedwater to MSF Evaporator. Full Scale Experience.- Calculation of Economic Indexes for Desalination Plants with and Without Desulphation Pretreatment System.- Kinetic Studies on Gel and Macroporous Anion Exchangers Using the Uranyl Sulfate/Sulfate Exchange.- Salt Conservation, Selectivity Reversal and Breakthrough Detection in Ion Exchange for Nitrate Removal.- Equilibrium and Diffusion Rate Effects of Univalent and Divalent Ions in a Bifunctional Resin.- Analysis of Ion Exchange Phenomena Occurring in Silicate Glasses Immersed in a Molten Salt Bath.- The Rim-Nut Process for Recovery of N/P Fertilizer From Sewage. Start-Up of Bari's Plant.- Ion Exchange for the Recycling of Wastewater Constituents.- Cation Exchange Softening Coupled with Electrodialysis for High Recovery Desalination.- Methods of Reducing Consumption of Sulphuric Acid in Regeneration of Strong Cation Exchangers in Water Desalination.- Design Methods for Ion Exchange Equipment.- Future Criteria for the Design and Manufacturing of Water Treatment Plants.- Water Softening for Food Processing.- Ion Exchange in the Food Industry.- Ion Exchange for the Recovery of Concentrated Ammonium Sulphate from the Process Condensate of an Ammonia-Urea Factory.- The Mechanism of Ion Exchange on Microcrystals of Inorganic Oxide-Hydroxides.- A Useful Method to Summarize Data in Ion Exchange - Influence of Temperature and Ionic Size.- Reversibility and Performances in Productive Ion-Exchange Chromatography.- Mossbauer and Electron Microprobe Studies of Precipitation Phenomena in Nafion Ion Exchange Membranes.- Ion Exchange Kinetics in Zeolite A.- Kinetics of Bulk and Interfacial Ionic Motion: The Microscopic Basis and Limits for the Nernst-Planck-Poisson System.- Nernst-Planck or No?.- Application of the Stefan-Maxwell Equations to Multicomponent Ion Exchange.- Concentration Polarization and Membrane Resistance Evaluation by Current Transient and Nernst-Planck Equations.

Surface analysis of polymer systems. 3. Zinc sulfide.cntdot.cadmium sulfide/Nafion

Abstract: X-ray photoelectron spectroscopy has been used to characterize the surfaces of Nafion films into which mixtures of CdS and ZnS have been precipitated by exposing ion-exchanged Nafion films to H2S. For all the cases studied, precipitation led to segregation of the metals from interior ion-exchange sites to the surface where small sulfide particles were formed. Irradiation of the films with visible light in the presence of aqueous 0.1 M Na2S solution produced H2 and some Cd. In the absence of ZnS, there was neither H2 nor Cd production. When ZnS and CdS were coprecipitated or when ZnS was precipitated after CdS, very active films were formed and irradiation changed the surface Zn/Cd ratio to a value near 5. When CdS followed Zns precipitation, irradiation did not change the Zn/Cd ratio from its initial value of unity and the films were inactive for photoassisted hydrogen generation. The results are discussed in light of other measurements on these materials which point to the importance of CdS surface state alteration by Zn.

EXAFS studies of Fe3+ neutralized Nafion: Interpretation of the second peak in the radial structure function

Abstract: Fe K‐edge extended x‐ray absorption fine structure (EXAFS) data are presented for ferric neutralized Nafion membranes treated in various ways. The transmission experiments were performed at room temperature. Some complementary Mossbauer data are also provided. Attention is focused on the second major peak in the EXAFS radial structure functions. In ferric neutralized Nafion, whether dehydrated in air or under reduced pressure, this peak is attributed to the neighboring Fe of an oxo‐bridged dimer, Fe–O–Fe. This dimer transforms into a dihydroxo‐bridged dimer Fe OHOH Fe upon heating to 150 °C in vacuo. If the heat treatment is done in water then microcrystalline Fe2O3 is formed. Immersion of the ferric neutralized Nafion membrane in KCl, K2CO3, KOH aqueous solutions, or even exposure to NH4OH vapor, results in precipitation of iron inside the membrane. The precipitate has a Fe–O distance of 1.94±0.02 A and a Fe–Fe distance of 3.11±0.05 A. Edge‐sharing FeO6 octahedra form the basis of the precipitate structure.

Surface analysis of semiconductor‐incorporated polymer systems: 2—Pt‐Nafion and Pt‐CdS‐Nafion

Abstract: Pt-Nafion (chemically reduced and sputtered Pt) and Pt-CdS-Nafion membranes were studied by x-ray photoelectron spectroscopy. The chemically deposited Pt was completely reduced to Pt0 and was more concentrated in the surface region than in the interior. The sputtered Pt (100 A thick) was distributed within the first several hundred Angstoms of the Nafion, probably involving Pt migration into it, during the RF sputtering process. Changes of the Pt(4f7/2) linewidth indicate interactions between CdS and Pt. The relatively high activity of the 100 A sputtered Pt-CdS-Nafion membrane for the photoassisted production of H2 in aqueous 0.1 M S2− solution is discussed.

New Electrolysis Methods

Abstract: New electrolysis methods for electro-organic syntheses were reviewed from the viewpoint of reduetion of difficulties in work-up and material preparation processes. The two phase electrolysis method has been applied to chlorination and cyanation of some aromatic compounds, using a phase transfer catalyst such as a quaternary ammonium salt. Addition of some Lewis acids to the system caused a favorable effect on yield. An ion exchange membrane was utilized as a supporting electrolyte using a conventional cell of two compartment equipped with a fine platinum mesh electrode pressed on the ion exchange membrane. An SPE electrolysis method was applied to electro-organic syntheses. The feasibility of the method was examined in some systems including mediatory systems fixed in an SPE material, usually Nafion. The fundamental properties of three methods were also reviewed.

Selective coupling of methanol and 2-methylpropan-1-ol to give 1-methoxy-2-methylpropane (methyl isobutyl ether)

Abstract: The superacid Nafion-H resin selectively catalyses the coupling of the two alcohols methanol and 2-methylpropan-1-ol to give methyl isobutyl ether.