Nafion

About: Nafion is a research topic. Over the lifetime, 9110 publications have been published within this topic receiving 320865 citations.

Oxygen and hydrogen permeation properties and water uptake of Nafion® 117 membrane and recast film for PEM fuel cell

Abstract: Oxygen and hydrogen permeability through Nafion® 117 membrane and recast Nafion film has been studied by means of gas chromatography at different values of temperature and gas relative humidity. Water uptake from the vapour phase by Nafion® 117 membrane and recast film has been investigated. It has been shown that oxygen and hydrogen permeability increases both with temperature and relative humidity of the gas, but water vapour uptake by both Nafion® 117 membrane and recast film decreased with increasing temperature. SEM studies have been performed on the membrane-electrode assembly obtained by impregnation/hot-pressing and on carbon/Nafion® composite; these have indicated that the active catalyst layer is porous with channels for the gas transport.

Solution chemistry of self-assembled graphene nanohybrids for high-performance flexible biosensors.

Abstract: We report the preparation of free-standing flexible conductive reduced graphene oxide/Nafion (RGON) hybrid films by a solution chemistry that utilizes self-assembly and directional convective-assembly. The hydrophobic backbone of Nafion provided well-defined integrated structures, on micro- and macroscales, for the construction of hybrid materials through self-assembly, while the hydrophilic sulfonate groups enabled highly stable dispersibility (∼0.5 mg/mL) and long-term stability (2 months) for graphene. The geometrically interlocked morphology of RGON produced a high degree of mechanical integrity in the hybrid films, while the interpenetrating network constructed favorable conduction pathways for charge transport. Importantly, the synergistic electrochemical characteristics of RGON were attributed to high conductivity (1176 S/m), facilitated electron transfer (ET), and low interfacial resistance. Consequently, RGON films obtained the excellent figure of merit as electrochemical biosensing platforms for...

Tuned Polymer Electrolyte Membranes Based on Aromatic Polyethers for Fuel Cell Applications

Abstract: Poly(arylene ether sulfone)-based ionomers containing sulfofluorenyl groups have been synthesized for applications to polymer electrolyte membrane fuel cells (PEMFCs). In order to achieve high proton conductivity and chemical, mechanical, and dimensional stability, the molecular structure of the ionomers has been optimized. Tough, flexible, and transparent membranes were obtained from a series of modified ionomers containing methyl groups with the ion-exchange capacity (IEC) ranging from 1.32 to 3.26 meq/g. Isopropylidene tetramethylbiphenylene moieties were more effective than the methyl-substituted fluorenyl groups in giving a high-IEC ionomer membrane with substantial stability to hydrolysis and oxidation. Dimensional stability was significantly improved for the methyl-substituted ionomer membranes compared to that of the non-methylated ones. This new ionomer membrane showed comparable proton conductivity to that of the perfluorinated ionomer membrane (Nafion 112) under a wide range of conditions (80-120 degrees C and 20-93% relative humidity (RH)). The highest proton conductivity of 0.3 S/cm was obtained at 80 degrees C and 93% RH. Although there is a decline of proton conductivity with time, after 10 000 h the proton conductivities were still at acceptable levels for fuel cell operation. The membranes retained their strength, flexibility, and high molecular weight after 10 000 h. Microscopic analyses revealed well-connected ionic clusters for the high-IEC membrane. A fuel cell operated using the polyether ionomer membrane showed better performance than that of Nafion at a low humidity of 20% RH and high temperature of 90 degrees C. Unlike the other hydrocarbon ionomers, the present membrane showed a lower resistance than expected from its conductivity, indicating superior water-holding capability at high temperature and low humidity.

Polymer Films on Electrodes. 8. Investigation of Charge-Transport Mechanisms in Nafion Polymer Modified Electrodes

Abstract: The mechanism of charge transport through Nafion polymers coated on glassy carbon electrodes and containing Cp2FeTMA+, R~(bpy),~+, and O~(bpy),~+ (where Cp2FeTMA+ is ((trimethylammonio)methyl)ferrocene, bpy = 2,2'-bipyridine) is described. The apparent diffusion coefficients, Dam,, of polymer modified electrodes, as measured by conventional electrochemical methods and which can include contributions from intermolecular electron transfer, are compared to the diffusion coefficients of actual mass transport of the electroactive species through the polymer, D,, as measured from the rate of permeation of the electroactive material. The results indicate that Dapp = D, for Cp2FeTMA+, Dapp 20, for Os(bpy),*+, and DaP4 = 15D, for Ru(bpy)t+. These results are discussed in terms of the Dahms-Ruff model, where the observed diffusional behavior is due to both physical diffusion of the electroactive species and an electron-transfer component that can contribute to the observed behavior. The contribution of the electron-exchange mechanism toward the value of Dapp decreases in the order of electroactive species, Ru(bpy),*+ >> O~(bpy),~+ 2 Cp2FeTMA+. A key question in the behavior of "polymer electrodes" (elec- trodes coated with a thin layer of polymer1-*) involves the mechanism of charge transport through the layers. The rate of charge transport frequently governs the rate of electrochemical and catalytic processes at such electrodes and has been the subject of numerous recent inve~tigations.~,~.~-" Charge can be trans- ported through the layer by electron transfer between redox centers, counterion diffusion, and diffusion of the electroactive species; the relative contribution of these effects is probably different for different kinds of polymer coatings.