Nafion

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

Electrical conductivity, ionic conductivity, optical absorption, and gas separation properties of ionically conductive polymer membranes embedded with Si microwire arrays

Abstract: The optical absorption, ionic conductivity, electronic conductivity, and gas separation properties have been evaluated for flexible composite films of ionically conductive polymers that contain partially embedded arrays of ordered, crystalline, p-type Si microwires. The cation exchange ionomer Nafion, and a recently developed anion exchange ionomer, poly(arylene ether sulfone) that contains quaternary ammonium groups (QAPSF), produced composite microwire array/ionomer membrane films that were suitable for operation in acidic or alkaline media, respectively. The ionic conductivity of the Si wire array/Nafion composite films in 2.0 M H_(2)SO_4(aq) was 71 mS cm^(−1), and the conductivity of the Si wire array/QAPSF composite films in 2.0 M KOH(aq) was 6.4 mS cm^(−1). Both values were comparable to the conductivities observed for films of these ionomers that did not contain embedded Si wire arrays. Two Si wire array/Nafion membranes were electrically connected in series, using a conducting polymer, to produce a trilayer, multifunctional membrane that exhibited an ionic conductivity in 2.0 M H_(2)SO)4(aq) of 57 mS cm^(−1) and an ohmic electrical contact, with an areal resistance of ~0.30 Ω cm^2, between the two physically separate embedded Si wire arrays. All of the wire array/ionomer composite membranes showed low rates of hydrogen crossover. Optical measurements indicated very low absorption (<3%) in the ion-exchange polymers but high light absorption (up to 80%) by the wire arrays even at normal incidence, attesting to the suitability of such multifunctional membranes for application in solar fuels production.

End-Group Cross-Linked Poly(arylene ether) for Proton Exchange Membranes

Abstract: End-group cross-linkable sulfonated poly(arylene ether) polymer (E-SFQK) was synthesized via direct polymerization of potassium 2,5-dihydroxybenzenesulfonate (SHQ) and decafluorobiphenyl (DFBP), followed by a reaction with ethynylphenol (EP). The cross-linking reaction of the ethynyl end group of E-SFQK was performed at 250 °C. After cross-linking, proton conductivity, water uptake, and swelling ratio of cross-linked membrane decreased from 0.16 (noncross-linked membrane) to 0.13 S/cm, from 86% to 42%, and from 31% to 13%, respectively. The effect of cross-linking time on proton conductivity, water uptake, and swelling ratio were also investigated. Methanol permeability of cross-linked membrane was compared with Nafion 117 due to solubility of noncross-linked membranes in methanol. The cross-linked membrane performed better, with a methanol permeability of 88 × 10−8 cm2/s, as compared with 154 × 10−8 cm2/s for Nafion 117. The cross-linked membrane also exhibited improved chemical resistance and oxidative ...

High‐Performance Nanofiber Fuel Cell Electrodes

Abstract: Catalysts are key cost components in proton-exchange membrane (PEM) fuel cells. Consequently, there has been ongoing research to improve electrode catalyst activity and durability, particularly for platinum-based cathodes in hydrogen/air PEM fuel cells. Herein, we present results on a nanofiber-structured oxygen reduction fuel cell cathode that was prepared by electrospinning a solution containing catalyst powder and polymer binder. The electrospun nanofiber mat, with an average fiber diameter of 470 nm, was hot-pressed onto a Nafion 212 membrane with a decal-processed anode and tested in H2/air and H2/O2 fuel cells. The nanofiber cathode performed extraordinarily well ; high power densities (more than 500 mWcm 2 at 0.6 V and 80 8C) were achieved at a very low platinum loading of 0.1 mgcm , the platinum mass activity was exceptionally high at 0.23 AmgPt , and the nanofiber electrode exhibited outstanding stability in a voltage cycling accelerated degradation test. Prior work on fuel cell electrodes has focused on eliminating platinum-group metal (PGM) catalysts entirely from the cathode, or on decreasing the loading of PGMs in the cathode by use of alloys, core–shell materials, 7] star-like structures, or other supports. 10] Another way to lower the catalyst loading is to alter the morphology of the cathode in a fuel cell membrane–electrode assembly (MEA) in order to maximize catalyst contact with reactant gases while maintaining a sufficient number of pathways for proton and electron conduction. Surprisingly, over the past twenty years, there has been little advancement on new fuel cell electrode constructs with improved catalyst utilization. Thus, most fuel cell MEAs are fabricated today using either : (i) a decal transfer method, (ii) a catalyst coated carbon paper or carbon cloth gas diffusion layer (GDL), or (iii) a catalyst coated PEM. Recently, researchers have attempted to fabricate new fuel cell electrode structures, such as electrosprayed layers of micrometer-size catalyst droplets, platinum nanowires, oriented platinum-coated whiskers (developed by 3M Corporation), and electrospun micrometer-sized core-sheath fibers reported by Asahi Glass Co (where a fiber core of Pt/C catalysts is covered by polyethylene oxide). While such new approaches are promising, none has lead to a substantial reduction in platinum catalyst loading for the cathode while maintaining high fuel cell power output and providing long-term electrode durability. Electrospinning is a well-known technique for producing polymer fibers with nanometer-sized diameters. Recently, it has been used successfully to fabricate proton-conducting fuel cell membranes, where a phase-separated composite structure was created with sulfonated polysulfone or perfluorosulfonic acid polymer nanofibers embedded in an inert (uncharged) polymer matrix. For the case of perfluorosulfonic acid (PFSA) nanofiber electrospinning, a small amount (0.3– 2.0 wt%) of an inert carrier polymer such as poly(ethylene oxide) or poly(acrylic acid) (PAA) must be added to the electrospinning solution because there is an insufficient number of PFSA polymer chain entanglements in normal organic electrospinning solvents. For the case of nanofiber electrode electrospinning, the present study builds upon these successful PFSA electrospinning studies. Thus, Nafion was used as the ionomer component of the catalyst ink and PAA was selected as the carrier polymer. The experimental apparatus used to fabricate the nanofiber mat electrode is shown schematically in Scheme 1. The cathode ink was a dispersion of Pt/C catalyst powder (40 wt% platinum on carbon black) in a mixed isopropyl alcohol/water solvent containing dissolved Nafion and PAA polymers. The ink was pumped out of a needle spinneret (22 gauge needle) and deformed into a Taylor cone by the strong applied potential at the needle tip, +7.0 kV relative to a grounded stainless steel rotating drum nanofiber collector. The spinneret-to-collector distance was fixed at 9 cm, and the flow rate of ink was 1.5 mLh . Nanofibers were collected on a carbon paper sheet that was fixed to the collector drum (rotating at 100 rpm). The drum oscillated horizontally to improve the uniformity of deposited nanofibers. The resulting electrospun nanofiber mat

Graphene Oxide-Impregnated PVA–STA Composite Polymer Electrolyte Membrane Separator for Power Generation in a Single-Chambered Microbial Fuel Cell

Abstract: The present study deals with the development and application of a proton-exchange polymer membrane separator consisting of graphene oxide (GO), poly(vinyl alcohol) (PVA), and silicotungstic acid (STA) in a single-chambered microbial fuel cell (sMFC). GO and the prepared membranes were characterized by FT-IR spectroscopy, XRD, SEM, TEM, and AC impedance analysis. Higher power was achieved with a 0.5 wt % GO-incorporated PVA–STA–GO membrane compared to a Nafion 117 membrane. The effects of oxygen crossover and membrane-cathode-assembly (MCA) area were evaluated in terms of current density and Coulombic efficiency. The electrochemical behavior of the membrane in an MFC was improved by adding different amounts of GO to the membrane to reduce biofouling and also to enhance proton conductivity. A maximum power density of 1.9 W/m3 was obtained when acetate wastewater was treated in an sMFC equipped with a PVA–STA–GO-based MCA. Therefore, PVA–STA–GO could be utilized as an efficient and inexpensive separator for ...