Showing papers on "Nafion published in 2004"
TL;DR: Light scattering experiments revealed that the radius of gyration had a linear dependence on the molar mass of the aggregates, which suggests that the particles are in the form of rods or ribbons, or at least some elongated structure.
Abstract: Equivalent weight (EW) is the number of grams of dry Nafion per mole of sulfonic acid groups when the material is in the acid form. This is an average EW in the sense that the comonomer sequence distribution (that is usually unknown to the investigator and largely unreported) gives a distribution in m in this formula. EW can be ascertained by acid-base titration, by analysis of atomic sulfur, and by FT-IR spectroscopy. The relationship between EW and m is EW ) 100m + 446 so that, for example, the side chains are separated by around 14 CF2 units in a membrane of 1100 EW. Common at the time of this writing are Nafion 117 films. The designation “117” refers to a film having 1100 EW and a nominal thickness of 0.007 in., although 115 and 112 films have also been available. Early-reported studies involved 1200 EW samples as well as special experimental varieties, some being rather thin. The equivalent weight is related to the property more often seen in the field of conventional ion exchange resins, namely the ion exchange capacity (IEC), by the equation IEC ) 1000/EW. The mention of the molecular weight of high equivalent weight (EW > 1000 g‚mol-1) Nafion is almost absent in the literature, although the range 105-106 Da has been mentioned. As this polymer does not form true solutions, the common methods of light scattering and gel permeation chromatography cannot be used to determine molecular weight as well as the size and shape of isolated, truly dissolved molecules. Studies of the structure of this polymer in solvent (albeit not a true solution) will be mentioned in the scattering section of this review. It should be noted that Curtin et al. performed size exclusion chromatography determinations of the molecular weight distribution in Nafion aqueous dispersions after they were heated to high temperatures (230, 250, and 270 °C).1 Before heating, there was a high molecular weight shoulder on a bimodal distribution, due to molecular aggregates, but this shoulder disappeared upon heating, which indicated that the aggregates were disrupted. The peaks for the monomodal distribution for the heated samples were all located at molecular weights slightly higher than 105 g‚mol-1. Also, light scattering experiments revealed that the radius of gyration had a linear dependence on the molar mass of the aggregates, which suggests that the particles are in the form of rods or ribbons, or at least some elongated structure. Nafion ionomers are usually derived from the thermoplastic -SO2F precursor form that can be extruded into sheets of required thickness. Strong interactions between the ionic groups are an obstacle to melt processing. This precursor does not possess the clustered morphology that will be of great concern in this article but does possess Teflon-like crystallinity which persists when the sulfonyl fluoride form is converted to, for example, the K+ form by reacting it with KOH in water and DMSO. Thereafter, the -SO3H form is achieved by soaking the film in a sufficiently concentrated aqueous acid solution. Extrusion of the sulfonyl fluoride precursor can cause microstructural orientation in the machine direction, * Address correspondence to either author. Phone: 601-266-5595/ 4480. Fax: 601-266-5635. E-mail: Kenneth.Mauritz@usm.edu; RBMoore@usm.edu. 4535 Chem. Rev. 2004, 104, 4535−4585
4,130 citations
TL;DR: Physical and functional attributes for recently developed Nafion ® products that satisfy emerging fuel cell requirements are reviewed in this article, including stronger, more durable membranes, and polymer dispersions of higher quality and consistency for catalyst inks and film formation.
695 citations
TL;DR: In this paper, the authors compared the physiochemical properties of Nafion 115 and a composite membrane of Zirconium phosphate (∼25 ¼wt.%) and found that the composite membrane has a greater rigidity that accounts for its improved fuel cell performance.
455 citations
TL;DR: The properties of hydrated Nafion polyelectrolyte are attributed to its nanophase-segregre... as mentioned in this paper, which is widely used in polymer electrolyte membrane fuel cells due to its high proton conductivity.
Abstract: Nafion polyelectrolyte is widely used in polymer electrolyte membrane fuel cells (PEMFC) due to its high proton conductivity. The properties of hydrated Nafion are attributed to its nanophase-segre...
417 citations
TL;DR: In this article, Sulfonated aromatic poly(ether ether ketones) (S-PEEKs) based membranes have been evaluated for fuel cell applications by determining the degree of sulfonation, water swelling, proton conductivity, methanol diffusivity and thermal stability.
399 citations
TL;DR: Ionically cross-linked polyelectrolyte complex (PEC) membranes of cationic chitosan (CS) and anionic poly(acrylic acid) (PAAc) were synthesized and assessed for applicability in fuel cells.
Abstract: Ionically cross-linked polyelectrolyte complex (PEC) membranes of cationic chitosan (CS) and anionic poly(acrylic acid) (PAAc) were synthesized and assessed for applicability in fuel cells. CS and PAAc were blended in different weight ratios and the resulting membranes were posttreated to enable the formation of the polyelectrolyte complex. The ionic cross-linking occurring on blending the polyelectrolytes excludes the need of using other cross-linking agents. These membranes were extensively characterized for morphology, their intermolecular interactions, thermal stability, and physicomechanical properties using SEM, FTIR, DSC, sorption studies, and tensile testing, respectively. Methanol permeability and proton conductivity were estimated and compared with respective values for Nafion 117. PEC membranes exhibited high ion exchange capacity (IEC), high proton conductivity, low methanol permeability, and adequate thermal and mechanical stability. Among the blends synthesized, the membrane blend with 50 wt...
345 citations
TL;DR: In this article, the complex Nafion structure over a large range of length scales was characterized using both scattering and microscopy techniques, and it was shown that fibrils correspond to elongated polymeric aggregates surrounded with the ionic charges.
Abstract: Using both scattering and microscopy techniques, we have characterized the complex Nafion structure over a large range of length scales. Analysis of experimental data from dry membrane to aqueous dispersion suggests an intrinsic fibrillar structure. The fibrils correspond to elongated polymeric aggregates surrounded with the ionic charges. In the Nafion membrane, the fibrils are entangled and collapsed with a degree of orientation at the mesoscopic scale. Upon swelling and temperature treatment, these aggregates are hydrated and dispersed in a colloidal suspension.
338 citations
TL;DR: In this paper, Nafion/silicon oxide (SiO2)/phosphotungstic acid (PWA) composite membranes were studied for the H2/O2 proton exchange membrane fuel cells (PEMFCs) operated above 100°C.
297 citations
TL;DR: In this article, Nafion ® -based organic/inorganic composite membranes with different inorganic heteropolyacid (HPA) additives such as phosphotungstic acid, silicotungstic acid, phosphomolybdic acid and silicomolybdenum-based acid were investigated for high temperature (120°C) low relative humidity (35%) operation.
292 citations
TL;DR: In this paper, transmission and attenuated total reflection (ATR) spectra of Nafion((R)) membrane and the difference of absorption peaks between two modes are presented, attributed to the different chemical environments of surface and bulk.
256 citations
TL;DR: In this paper, the authors investigated the methanol permeability of directly copolymerized 4,4′-biphenol based disulfonated poly(arylene ether sulfone) copolymers.
TL;DR: A new amperometric biosensor, based on adsorption of glucose oxidase (GOD) at the platinum nanoparticle-modified carbon nanotube (CNT) electrode, is presented in this article.
TL;DR: In this paper, the authors examined the dependence of optimum Nafion content in the catalyst layer on platinum loading and found that the best performance was obtained at different nafion loadings of 20, 40 and 50 ¼, respectively.
TL;DR: In this paper, the authors investigated the transport mechanisms of ions and water molecules in perfluorosulfonated ionomer membranes, including Nafion, Aciplex, and Flemion types.
Abstract: To clarify transport mechanisms of ions and water molecules in perfluorosulfonated ionomer membranes, various membranes, such as one Nafion, two Aciplex, and four Flemion types, having different equivalent weight values (EW) were examined. H-, Li-, and Na-form samples were prepared for each membrane by immersion in 0.03 M HCl, LiCl, and NaCl aqueous solutions, and their properties in the fully hydrated state were investigated systematically. The water content of the membranes showed the tendency that the size and/or the number of ionic cluster region increases with decreasing EW value and the Li-form membranes have the most largely expanded ionic cluster regions. The ionic conductivity of the H-form membranes was considerably higher than that of the Li- and Na-form membranes. It was suggested that the proton in the membranes transports by the hopping mechanism and the Li+ and Na+ ions by the vehicle mechanism. In addition, the ionic conductivity of all membranes increased with increasing water content wit...
TL;DR: In this article, Proton exchange membranes (PEM) have emerged as an essential factor in the technology race and have played an integral part in the success of recent work in portable, stationary and transportation applications.
TL;DR: In this article, the effect of the fabrication method and the thickness of the gas diffusion layer and the impregnation method of Nafion solution on the cell performance was investigated, and unit cell tests were performed.
TL;DR: The ability to immobilize dehydrogenase enzymes in Nafion that has been modified with quaternary ammonium bromides is examined to determine the activity of the immobilized enzyme and to examine the transport of coenzyme within the membrane.
TL;DR: The results indicated that the composite film had more open structures and a larger surface area allowing faster diffusion of Ru(bpy)(3)(2+) and that the CNT could adsorb and also acted as conducting pathways to connect Ru( bpy)( 3)(2-) sites to the electrode.
Abstract: The electrochemistry and electrogenerated chemiluminescence (ECL) of ruthenium(II) tris(bipyridine) (Ru(bpy)32+) ion-exchanged in carbon nanotube (CNT)/Nafion composite films were investigated with tripropylamine (TPA) as a coreactant at a glassy carbon (GC) electrode. The major goal of this work was to investigate and develop new materials and immobilization approaches for the fabrication of ECL-based sensors with improved sensitivity, reactivity, and long-term stability. Ru(bpy)32+ could be strongly incorporated into Nafion film, but the rate of charge transfer was relative slow and its stability was also problematic. The interfusion of CNT in Nafion resulted in a high peak current of Ru(bpy)32+ and high ECL intensity. The results indicated that the composite film had more open structures and a larger surface area allowing faster diffusion of Ru(bpy)32+ and that the CNT could adsorb Ru(bpy)32+ and also acted as conducting pathways to connect Ru(bpy)32+ sites to the electrode. In the present work, the se...
TL;DR: In this article, two novel sulfonated diamine isomers, 2,2′-bis(3-sulfopropoxy)benzidine (2,2''-BSPB) and 3,3''-bis (3-SPSPoxy)Benzidine(3, 3''-SSPB), were successfully synthesized and showed high proton conductivities with sulfonic acid groups in the side chains.
Abstract: Two novel sulfonated diamine isomers, 2,2′-bis(3-sulfopropoxy)benzidine (2,2′-BSPB) and 3,3′-bis(3-sulfopropoxy)benzidine (3,3′-BSPB), were successfully synthesized and the highly sulfonated polyimides (SPIs) with sulfonic acid groups in the side chains were prepared from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA) and BSPB monomers. Transmission electron microscopy (TEM) analysis revealed that these side-chain-type SPI membranes have a microphase-separated structure composed of hydrophilic side chain domains and hydrophobic polyimide main chain domains. They showed high proton conductivities similar to or higher than those of Nafion 117 in the high relative humidity range (>70% RH). The proton conducting behavior was analyzed by percolation theory. Despite their high ion exchange capacity (IEC = 2.89 meq. g−1) and high water uptakes, they displayed much better water stability than common sulfonated polyimides with the sulfonic acid groups directly bonded to the polymer backbone. This is probably due to the microphase-separated structure of the membrane and the strong basicity of BSPB diamine moieties resulting from the electron donating effect of the propoxy groups. The sulfopropoxy groups were stable against aging in acidic aqueous solution at 373 K. Both the polyimide membranes showed good mechanical strength under high moisture conditions (about 6 GPa at 90% RH) and displayed anisotropic membrane swelling.
TL;DR: In this paper, the authors examined the correlation of platinum loading and optimum Nafion content in the electrode and found that the optimum nafion requirement depends on the Pt loading and it increases with decrease in Pt loading.
TL;DR: Results suggest that the CNT-based electrodes (p-CNT/Nafion/GC), which were prepared by using Nafion to solubilize and further immobilize CNTs on GC electrodes, show striking analytical properties of good stability and reproducibility and strong ability against electrode fouling.
TL;DR: A series of sulfonated polyimide copolymers (FSPIH-X; X refers to molar percentage of bis(trifluoromethyl)biphenylene content) with X from 0 to 60 mol % were synthesized, of which electrolyte properties were investigated as mentioned in this paper.
Abstract: A series of sulfonated polyimide copolymers (FSPIH-X; X refers to molar percentage of bis(trifluoromethyl)biphenylene content) with X from 0 to 60 mol % were synthesized, of which electrolyte properties were investigated and compared to those of the perfluorinated ionomer (Nafion 112). FSPIH-X membranes are thermally stable with no glass transition temperature observed below the decomposition temperature (280 °C). Oxidative stability of the membranes is improved with an increase in the content of trifluoromethyl substituents in the copolymer structure. FSPIH-60 endured for more than 9 h in Fenton's reagent at 80 °C. Bis(trifluoromethyl)biphenylene groups with the molecular size of 6.1 A make each polymer chain separate and produce space to hold water molecules despite their hydrophobic property so that the maximum water uptake was observed for FSPIH-20. Unlike the fluorene groups containing polyimides (SPIH-X), a strong water confinement effect was not obtained for FSPIH-X. The optimum composition of bis(...
TL;DR: In this paper, the physical and chemical changes in fuel cell membranes that result from Freeze/Thaw (F/T) cycling which might occur in electric vehicles were analyzed and the analytical results shed some light on the relationship of temperature cycling to membrane structure, water management, ionic conductivity, gas permeability and mechanical strength.
Abstract: A study was conducted to understand the physical and chemical changes in fuel cell membranes that result from Freeze/Thaw (F/T) cycling which might occur in electric vehicles. Nafion™ membranes and membrane electrode assemblies (MEA) were subjected to 385 temperature cycles between +80 °C and –40 °C over a period of three months to examine the effects on key properties. These studies were done on both compressed and uncompressed materials in the un-humidified state. Although no catastrophic failures were seen, the analytical results shed some light on the relationship of temperature cycling to membrane structure, water management, ionic conductivity, gas permeability and mechanical strength. Changes in water swelling behavior and dry densities were noted and the effect on ionic conductivity and cell performance was examined. The impact on catalyst activity and structural integrity of MEAs was evaluated electrochemically.
TL;DR: In this article, a series of sulfonated polyimide copolymers (SPIH-X) containing 0−60 mol % of fluorenyl groups as hydrophobic component were synthesized, of which electrolyte properties were investigated and compared to those of the perfluorinated ionomer (Nafion 112).
Abstract: Novel sulfonated polyimide copolymers as electrolytes for high-temperature fuel cell applications are reported. A series of sulfonated polyimide copolymers (SPIH-X; X refers to molar percentage of fluorenyl content) containing 0−60 mol % of fluorenyl groups as hydrophobic component were synthesized, of which electrolyte properties were investigated and compared to those of the perfluorinated ionomer (Nafion 112). High-molecular-weight copolymers with good film-forming capability were obtained. Thermal stability with decomposition temperature of ca. 280 °C and no glass transition temperature was confirmed for the copolymers. SPIH shows unique water uptake behavior with the maximum value of 57 wt % at X = 30. Water molecules absorbed in the electrolyte membrane with this specific composition do not evaporate easily so that the high proton conductivity of 1.67 S cm-1 was obtained at 120 °C and 100% RH. The branching and cross-linking of SPIH-30 were carried out by applying 2 mol % of trifunctional monomer (m...
TL;DR: Chitosan membranes crosslinked in sulfuric acid are evaluated for their thermal stability, water absorption and proton conductivity properties as alternative proton exchange membrane (PEM) material for application in fuel cells.
TL;DR: In this article, an accelerated degradation test of selected membranes was carried out to determine their stability in the fully charged positive electrolyte solution of the vanadium redox battery, where each membrane was soaked in both 1.0 and 0.1 M V(V) solutions for extended periods of time and UV-visible spectroscopy was used to determine the rate of oxidation of the membrane by V (V) to produce V(IV) ions in solution.
Abstract: Accelerated degradation tests of selected membranes were carried out to determine their stability in the fully charged positive electrolyte solution of the vanadium redox battery. Each membrane was soaked in both 1.0 and 0.1 M V(V) solutions for extended periods of time and UV–visible spectroscopy was used to determine the rate of oxidation of the membrane by V(V) to produce V(IV) ions in solution. The membranes were then evaluated for any changes in their resistance, IEC, diffusivity and water transfer properties. FESEM was used to analyse the membranes for physical damage. Different trends were observed in the 1.0 and 0.1 M V(V) electrolytes. Of the membranes studied, Nafion 112E/H+ showed the worst stability in the 0.1 M V(V) solution but one of the best stabilities in 1.0 M V(V). The dilute V(V) electrolyte appears to enter the pores of the membrane more readily as the membranes swell significantly in this solution. The 0.1 M V(V) solution therefore causes accelerated deterioration of the membrane performance as a result of physical destruction, chemical modification or a combination of both. The effect is more pronounced in the membranes that have a higher degree of swelling in the vanadium electrolyte.
TL;DR: In this article, the structural orientation of Nafion films in an ambient environment and under stretching was analyzed using small/wide-angle X-ray scattering, based on the absolute values of Hermans' orientation factor.
Abstract: The structural orientation in Nafion films in an ambient environment and under stretching is analyzed using small/wide-angle X-ray scattering. On the basis of the absolute values of Hermans' orientation factor, we characterize the structural anisotropy at different length scales (between angstroms and several hundreds of angstroms) in agreement with a previously proposed fibrillar model of the Nafion membrane. Bundles of elongated polymeric aggregates orient at small draw ratios, together with an orientation of the aggregates within such a bundle. The crystal structure of this semicrystalline polymer is analyzed, and we show that the crystallinity of the Nafion film does not change as a function of the draw ratio.
ENEA1
TL;DR: In this article, conductivity measurements of Nafion® 112, 115 and 117 membranes in the normal direction were made by means of impedance spectroscopy as a function of temperature, and the data showed that Nafions are really isotropic and that tangential and normal direction conductivity measurement gave the same results when the same hydration level was utilized.
TL;DR: In this paper, the effect of Nafion loading on the electrode polarization characteristics of a proton exchange membrane fuel cell was studied with a macrohomogeneous model and the composition dependence of performance was rationalized by first relating mass fractions of the different components to their volume fractions and thereafter involving concepts of percolation theory to parameterize effective properties of the cathode catalyst layers.
Abstract: The effect of Nafion loading on the electrode polarization characteristics of a proton exchange membrane fuel cell is studied with a macrohomogeneous model. The composition dependence of performance is rationalized by first relating mass fractions of the different components to their volume fractions and thereafter involving concepts of percolation theory to parameterize effective properties of the cathode catalyst layers. In particular, we explore systematically the effect of Nafion content on the performance. For a uniform layer, the best performance is obtained with a Nafion content of about 35 wt %, representing an optimum balance of proton transport, oxygen diffusion, and electrochemically active surface area. With the help of this modeling tool, we propose a nonuniform Nation catalyst layer and the modeling indicates that such a layer improves performance. Our preliminary experiments (to appear in Part II) confirm this claim. The two cases of nonuniform Nation distribution across the entire thickness include: a three-sublayer structure with equally thick layers, simulating a constant gradient, and a two-sublayer structure with variable thickness of the sublayers. Compared with the optimum Nafion content (35 wt %) in uniform distribution, the three-sublayer structure with higher Nation content on the membrane side exhibits significantly enhanced performance.
TL;DR: In this article, the structural and functional properties of different Nafion 117 membranes filled with zirconium phosphate were studied by numerous techniques like, e.g., cryo scanning electron microscopy, dynamic mechanical analysis, and X-ray diffraction (XRD) to understand the effective solvent diffusion in hybrid membranes.