Nafion polymers

A very similar idea is the use of ion exchanging polymers into which redox active ions can be incorporated by equilibration with an adherent solution. Sulfonated perfluoro polymers (Nafion), polyvinylsulfonic acid , and polystyrene... 

Multilayered Structures with Metal Cations Based on LB Films ofPerfluorinated Sulfoacid Polymer (Nafion-wpe)... 

LB Films of Perfluorinated Sulfoacid Polymer (Nafion-Type). 

The use of perfluorinated ionic polymer membranes to separate the catholyte and anolyte compartments in chloroalkali cells has been growing in importance over the past 25 years as these units have replaced the older Castner-Kellncr cells which depend upon large quantities of toxic mercury for their operation. The first perfluorinated ionic polymer, Nafion , was developed by Du Pont and was manufactured by the copolymerization of tetrafluoroethene with monomer 2. 

It should be possible, using this technique to prepare a number of different functionalized fluorocarbon polymers with varying physical, thermal, and chemical properties that should complement or compete in applications established for the sulfonic acid functionalized fluorocarbon polymer Nafion , which has been reported previously (45). 

Electron hopping is not the only mechanism by which a multilayer film containing an electroactive species can be electrochemically oxidized or reduced. Consider an electrode surface that has been coated with a film of the cation-exchange polymer Nafion (Table 13.2). Let us assume that the electroactive cation Fe3+ has been ion-exchanged into this Nafion film (e.g., Eq. 13.4). In principle, the Fe3+ in this film can be reduced via the following redox reaction ... 

Research into chemically modified electrodes has led to a number of new ways to build chemical selectivity into films that can be coated onto electrode surfaces. Perhaps the simplest example is the use of the polymer Nafion (see Table 13.2) to make selective electrodes for basic research in neurophysiology [88]. Starting with the pioneering investigations by Ralph Adams, electrochemists have become interested in the electrochemical detection of a class of amine-based neurotransmitters in living organisms. The quintessential example of this class of neurotransmitters is the molecule dopamine, which can be electrochemically oxidized via the following redox reaction ... 

When Ru-red was used as a catalyst in the presence of a large excess of Ce(IV) oxidant (Scheme 19.1), the rate of 02 evolution was first order with respect to the catalyst concentration, showing that Ru-red is capable of 4-electron oxidation of water. By the decomposition of the Ru-red, N2 was formed its formation rate was second order with respect to the catalyst concentration, showing that the decomposition is bimolecular. The decomposition distance in a polymer (Nafion) matrix was estimated by assuming the random distribution of the catalyst molecule in the matrix. The probability density P(r) of the distance between the nearest neighbor molecules (r nm) is represented by Eq. (19.5) according to the Poisson statistics... 

A convenient solid of perfluorinated-sulfonic acid can be made readily from DuPont s commercially available Nafion brand ion membrane resins. Powder granules of the 1200-EW polymer, Nafion 501, have been used most frequently in catalytic applications the price in the K+ form of the perfluorosulfonic salt, 501X, was 650/kg in 1981. Because only the potassium salt derivative is commercially available, the salt is converted to the free sulfonic acid by treatment with mineral acid. A standard procedure for the conversion is described below. This procedure also serves to regenerate the resin in various catalytic cycles. 

For PEMFCs, the solid electrolytes are polymer membranes polymers modified to include ions, usually sulfonic groups. One of the most widely used membranes today is the polymer Nafion , created by the DuPont company. These membranes have aliphatic perfluorinated backbones with ether-linked side chains ending in sulfonate cation exchange groups [6, 7], Nafion is a copolymer of tetrafluoroethylene and sulfonyl fluoride vinyl ether [8] and has a semi-crystalline structure [9], This structure (which resembles Teflon ) gives Nafion long-term stability in oxidative or reductive conditions. The sulfonic groups of the polymers facilitate the transport of protons. The polymers consist of hydrophilic and hydrophobic domains that allow the transport of protons from the anode to the cathode [10, 11],... 

Wang et al. [55] have reported on the ability of the perfluorosulfonated polymer Nafion to solubilize SWCNTs and MWCNTs. They proposed that a homogeneous, well-distributed solution of Nafion/CNTs was obtained with 0.5 % v/v (in 0.05 M phosphate buffer pH 7.4) and 5% v/v polymer solution for SWCNTs and MWCNTs, respectively. A polished GCE was modified with 20 pL of a 2 mg/mL CNTs solution in 0.5 % w/w Nafion. The coating was allowed to... 

Advances in electrochemical systems rest in large measure with the evolution of new materials that exhibit chemical stability in severe environments, high electrocatalytic activity, rapid ion conductivity, etc. Examples include RuOx-TiOy-Ti electrocatalysts, the polymer Nafion, yttrium-stabilized zirconate and beta-alumina electrolytes, and metastable alloys produced by rapid solidification processing. 

Polymer-(Nafion-, hydrogel-) coated amperometric and potentiometric sensors... 

Nafion is commercially available as Nafion NR50 (DuPont) in the form of relatively large (2-3 mm) beads. A disadvantage of these beads is the low surface area (typically < 0.02 m g ) [8]. Water-selective Perma Pure membranes also consist of the polymer Nafion and were especially developed for removal of water from gas-phase streams [9]. Nafion is also available as a 5 % solution in a mixture of lower aliphatie alcohols and water [10]. 

The membrane in a PEM cell is made from a sulfinate polymer Nafion, which only lets protons through because there are sulfinate (SO4) molecules in the polymer, which contain oxygen atoms that are slightly negatively charged. The positively charged protons can weakly bind to them, which allows protons to permeate the membrane, and jump from one sulfinate molecule to another across the membrane with help from thermal fluctuations and the electric field created across the membrane by the electron flow (Figure 7.10). 

Krishnan, M., White. J. R.. Fox, M. A., Bard. A. J. (1983). Integrated chemical. systems Photocatalysis at. semiconductors incorporated into polymer (Nafion)/mediator... 

Catalytic oxidation of CO has been studied intensively, mainly for the purpose of removing CO from exhaust gases. The main information is provided in patents. Polymer chelates of copper and platinum are most often used for this purpose, as well as platinum metals bound with a completely fiuorinated polymer Nafion . 

Application of transition metal hexacyanoferrates for development of biosensors was first announced by our group in 1994 [118]. The goal was to substitute platinum as the most commonly used hydrogen peroxide transducer for Prussian blue-modified electrode. The enzyme glucose oxidase was immobilized on the top of the transducer in the polymer (Nafion) membrane. The resulting biosensor showed advantageous characteristics of both sensitivity and selectivity in the presence of commonly tested reductants, such as ascorbate and paracetamol. 

As a proton-conducting polymer, Nafion (a perfluorosulfonic acid polymer) has high ionic conductivity and has also been investigated as an electrolyte for different types of solid-state ESs [852-858]. It has been found that high scan rates could be achieved for ESs with Nafion electrolytes [854,855,859]. 

We will return to the discussion on the relationship between structure and properties in Nafion and Nafion-based membranes in a next section. The modification of NafiOTi with inorganic and organic compounds has been investigated [3,9] in order to improve the performance of these perfluorinated membranes in DAFC by reducing the methanol crossover, while enhancing water retention and thermal stability. Next subsections are devoted to describe the different types of inor-ganic/Nafion composites and polymer/Nafion blends that have been reported in the literature in relation to its use as electrolytes in DAFC. 

The higher i -potentials are found on polar polymers without any functional surface groups (e.g. PLEA). Polymers of similar surface chemistry exhibit similar potentials, e.g. three samples of PTFE foils differing only in the thickness, or HDPE and LDPE. Only one of used polymers, Nafion, contains sulfonic acid groups on the surface disposed to dissociation in contact with electrolyte. This dissociation is a key action to zeta potential generation at thie polymer. Due to this dissociation zeta potential of Nafion is the lowest. In some cases it can be even positive due to this [40]. 

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