Ion-exchange membranes Nafion

See also -> ions-exchange membrane, -> Nafion , -> poly electrolytes, -> polymer electrolytes. 

Table 2 Coordination numbers and interatomic distances determined from EXAFS spectroscopy of ion-exchanged membranes Nafion - 17-Zr, sPEEK-Zr and crystalline ZrOCl2...

For simplicity, assume the height of both chambers are 100 pm and the conductivity for both anolyte and catholyte are 0.017 S cm the calculated is 1.2 O cm. According to prior art, r , resistivity of the ion exchange membrane (Nafion 117, for instance) is approximately 10 Q cm in phosphate buffer medium, r, resistivity of cathode is also low when the current density is low enough that the concentration loss is not a dominating factor, which is the case in the ohmic region. As a result, anode resistivity dominates over the total resistivity in microscale MFCs. 

Ion exchanger membranes NAFION (cation exch.) diverse cations... 

To keep the consumption of the valuable platinum low, thin foils have been glued to a graphite support [34] or thin-layers of platinum have been sputtered on to a glass base [59]. Platinum can be used in a particle electrode by plating silica gel with platinum [60], or in a solid polymer electrolyte where platinum is incorporated into a nafion ion exchange membrane [61]. 

In the membrane-cell process, highly selective ion-exchange membranes of Du Font s Nation type are used which allow only the sodium ions to pass. Thus, in the anode compartment an alkali solution of high purity is produced. The introduction of Nafion-type membranes in chlor-alkali electrolyzers led to a significant improvement in their efficiency. Today, most new chlor-alkafi installations use the membrane technology. Unfortunately, the cost of Nafion-type membranes is still very high. 

An improvement in this process was shown by Fujita [17] among others [e.g. 18] who used an ion-exchange membrane such as Nafion as the electrolyte. The cathode... 

The potential use of polymeric ion-exchange membranes in the next generation single-ion secondary lithium polymer batteries was shown by Sachan et al 84,85 Conductivities exceeding 10 S/cm with transference numbers of unity were achieved for Nafion converted to the Li+ salt form. 

All work has been accomplished using perfluorosulfonate ion exchange membranes manufactured by E.l. duPont and sold under the trade name Nafion. Nafion is a copolymer of polytetrafluoroethy-lene (PTFE) and polysulfonylfluoride vinyl ether containing pendent sulfonic acid groups. The sulfonic acid groups are chemically bound to the perfluorocarbon backbone. 

Concentration Method. The concentration procedure that was developed and evaluated was a RO-Donnan dialysis system (4). The initial objective during method development was to conduct membranescreening tests to evaluate the suitability of various RO and ion-exchange membranes. The four membranes considered for final evaluation on the basis of solute rejection, chlorine stability, and artifact production were the cellulose acetate and FT-30 (Film Tec) RO membranes, the Nafion cation-exchange membrane, and the ION AC MA 3475 anion-exchange membrane. 

Divided parallel plate flow-through cells are especially advantageous for laboratory use because they can easily be constructed from two Teflon cell body halves according to Figure 22.14. In such a construction, ion-exchange membranes can easily be applied for the separation of the two cell compartments. For anodic oxidations, cation exchange membranes like Nafion are most often used. For cathodic reactions, anion exchange membranes are applicable. Asbestos or microporous membranes can also be used as separators. 

Perfluorosulfonic acid polymers, for example, Nafion, or ionic and cross-linked polystyrene derivatives, are the best known examples of ion-exchange membrane materials (see also Section 2.6.4). 

Divided cells — Electrochemical cells divided by sintered glass, ceramics, or ion-exchange membrane (e.g., - Nafion) into two or three compartments. The semipermeable separators should avoid mixing of anolyte and - catholyte and/or to isolate the reference electrode from the studied solution, but simultaneously maintain the cell resistance as low as possible. The two- or three-compartment cells are typically used a) for preparative electrolytic experiments to prevent mixing of products and intermediates of anodic and cathodic reactions, respectively b) for experiments where different composition of the solution should be used for anodic and cathodic compartment c) when a component of the reference electrode (e.g., water, halide ions etc.) may interfere with the studied compounds or with the electrode. For very sensitive systems additional bridge compartments can be added. 

Figure 5.15. Schematic cell for the measurement of through-plane conductivity [13]. (Reprinted from Journal of Electroanalytical Chemistry, 449, Gardner CL, Anantaraman AV. Studies on ion-exchange membranes. II. Measurement of the anisotropic conductance of Nafion , 209-14, 1998, with permission from Elsevier.)...

Anantaraman AV, Gardner CL (1996) Studies on ion-exchange membranes. Part 1. effect of humidity on the conductivity of Nafion . J Electroanal Chem 414 115-20... 

The /J-sultone formed in the reaction of sulfur trioxide with tetrafluoroethenc itself is a key intermediate in the synthesis of Nafion polymers, which have commercial use as ion-exchange membranes. Furthermore, perfluorovinylsulfonyl fluoride (3) is transformed into mainly the /Tsultone 4 when heated with sulfur trioxide at elevated temperature. ... 

Figure 3.42. Segment of a perfluorinated sulphonate ion exchange membrane of Nafion t) e. The top polymer chain is made from C atoms as backbone and pairs of F atoms on the sides (end hydrogens are replaced when the chain is enlarged). The acid FISOj molecule promoting H transport is attached at the end of an arm of 4 CFj molecules interspersed with two O atoms, and with one F replaced by a CFj group.

A1 over H" for Nafion 117 at 50 meq/L solution concentration. Thus, at anytime during the process, ai N significantly greater than qii within the ion-exchange membrane. In fact, the qAi,i/Q value on feed surface was never below 0.75 during the entire period of the experiment. Considering the extreme case where hydrogen ion is essentially a trace species compared to aluminum ion, i.e., qAi qn. Equation 34.32 reduces to... 

Another design that is used in chlo-ralkali electrolysis, water electrolysis, and electro-organic synthesis [95-97] is the solid polymer electrolyte (SPE) cell, where an ion exchanger membrane, for example, Nafion , serves as the electrolyte, Fig. 9. The microporous catalytic reaction layers are pressed directly onto the membrane with porous current collectors allowing transport of dissolved reactants and gaseous products into and out of the reaction layer. 

In a similar vein, Sakai, Takenaka and Torikai produced Nafion/metal microcomposites by reducing palladium, rhodium, platinum and silver ion-exchanged membranes with H, at high temperatures (100-300°C) (26). The affected metal clusters, distributed homogeneously, were about 50 A in size. As in Risen s work, a polymer matrix template effect appears to be operative. These systems were considered and evaluated within the context of gas separations technology. 

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