Nafion cation exchange

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. 

For laboratory-scale reactions, this electrocatalytic AD generally is performed in a glass H-type cell in which the anode and cathode compartments are separated by a semipermeable Nafion cation-exchange membrane and platinum electrodes are used. A 5% aqueous solution of phosphoric acid is used in the cathode compartment, and the reaction in the anode compartment is stirred vigorously, Under a controlled anode potential of 0.4 V (vs. Ag/AgCl) and with (DHQD)2-PHAL as chiral ligand, a-methylstyrene was converted to 7 -2-pheny 1-1,2-propanediol in 15 h with the electrical consumption of 2.1 F/mol. The product was isolated in 100% yield with 92% ee [ 37],... 

Fry has used a similar system for the enzymatic reduction of pyruvate to L-lactate. In this case, the one-electron transfer redox catalyst, methyl viologen, and the lipoamide dehydrogenase are coimmobilized within a Nafion cation-exchange layer on the surface of a reticulated vitreous carbon electrode. As production enzyme, L-lactate dehydrogenase (LDH) was employed [48], which was later stabilized considerably in the form of cross-... 

Phthalonitrile was reduced at controlled potential in alcoholic solution at a C cathode in a two-compartment cell in which cathode and anode were separated by a Nafion cation-exchange membrane. The anolyte contained metallic salts such as CUSO4, NiS04, etc. The products formed in the cathode compartment were metal phthalocyanine complexes. Low yields were obtained when the metal ions were placed into the cathode compartment. The phthalonitrile radical anion formed by a 1-electron transfer was invoked as being important in the cyclization process leading to the metal complexes. Several intermediates... 

In the zinc/bromine cell, the halogen is stored in the electrolyte as a polybromide (mainly Bra ) and hence a separator is essential Nafion cation exchange membrane has again been used. The electrolyte is aqueous zinc bromide with tetraalkyl-ammonium bromide to aid the bromine complex formation. 

The electrochemical reactor is of a divided configuration using a Nafion cation exchange membrane to separate a cathode of either lead, tin or carbon from the oxygen evolving mode. The chemical reduction step takes place in an external reactor and can produce yields of colloidal sulphur of greater than 90%. 

The upper part of Fig. 2 shows the molecular structure of the perfluorinated Nafion cation exchange membranes with sulfonic acid as well as with carboxylic acid groups as fixed ions. These are covalently bonded at the end of side chains of the PTFE (polytetrafiuoroethylene) polymer backbone. The polymer has excellent chemical and thermal stability, similar to PTFE [9]. 

Fig. 2 Structure of the Nafion cation exchange membrane (Based on [9])...

Figure 7.22. Structure of a Nafion cation exchanger membrane. Hydrophilic clusters are surrounded partially by hydrophobic PTFE regions. Cations like H can move from one hydrophilic cluster to the next etc.

Swider, K. E. and Rolison, D. R. (2000) Reduced poisoning of platinum fuel-cell electrocatalysts supported on desulfurized carbon. Electrochem. Solid-State Lett. 3,4-6 Tandon, R. and Pintauro, P. N. (1997) Divalent/monovalent cation uptake selectivity in a Nafion cation-exchange membrane experimental and modeling studies. J. Membr. Sci. 136, 207-219 Tan, J., Chao, Y. J., Van Zee, J. W. and Lee, W.-K. (2007) Degradation of elastomeric gasket materials in PEM fuel cells. Mater. Sci. Eng. A, 445-446, 669-675 Tawfik, H., Hung, Y. and Mahajan, D. (2(X)7) Meted bipolar plates for PEM fuel cell - A review. J. Power Sources 163, 755-767... 

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