Cation Conductive Membranes

While Nafion , a perfluorinated polymer developed by DuPont, is the most commonly used proton conductive polymer electrolyte membrane it is an insufficient solution in a number of areas. It has high cationic transport (approximately 9.56 5/cm) [8] but also has high levels of methanol fuel crossover, slow anode kinetics and very high cost [12]. Fuel cell membrane performance can be estimated from the ratio of proton conductivity (a) to methanol permeability (P). The higher the value of a/P, the better the membrane performance would be [13]. Chitosan has been shown to have a much lower methanol permeability than Nafion [14], and as such, a great deal of attention focused on developing chitosan membranes with high levels of ionic conduction and low methanol permeability as delineated in Table 3.1. 

The work of Binsu et al. has focused on the phosphonic functionalization of chitosan combined with polyvinyl alcohol and has yielded the highest fuel cell 

Modification Conductivity Type Measured Conductivity (S/cm) Methanol Permeability (cm2/s) Fuel Cell Membrane Efficiency 

Chitosan-oxide composite Proton [24] 10- to 10-2 at 25°C Not reported Not reported 

---

In an approach suggested by Nagy et al. [50], the reference signal will be produced by two separate electrodes consisting of Ag/AgCl layers covered with an anion and cation conducting membrane, respectively. The electrodes are connected in parallel via a resistor and intrinsically respond to monovalent cations... 

This material was first synthesized in the middle 1960s by E.I. Du Pont de Nemours and Co., and was soon recognized as an outstanding ion conductor for laboratory as well as for industrial electrochemistry. The perfluorinated polymeric backbone is responsible for the good chemical and thermal stability of the polymer. Nation membrane swollen with an electrolyte solution shows high cation conductivity, whereas the transport of anions is almost entirely suppressed. This so-called permselectivity (cf. Section 6.2.1) is a characteristic advantage of Nation in comparison with classical ion-exchange polymers, in which the selective ion transport is usually not so pronounced. 

Fesenko, E., Kolesnikov, S. S. and Lyubarsky, A. L. Induction by cyclic GMP of cationic conductance in plasma membrane of retinal rod outer segment. Nature 313 310-313,1985. 

In 1973, Dupont began to commercialize their first perfluorosulfonic add cation exchange membrane, Nafion. Since then until now, Nafion has been attracting much attention because of its superb chemical and thermal stability, high ionic conductivity, excellent permselectivity and good mechanical strength. Many approaches have been proposed to use this unique material as a modifier of electrochemical electrode surfaces. 

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. 

Nakano, A. Xie, Q. Mallen, J. V. Echegoyen, L. Gokel, G. W., (1990) Synthesis of a membrane-insertable, sodium cation conducting channel kinetic analysis by dynamic sodium-23 NMR J. Am. Chem. Soc. 112, 1287-1289. 

This idea is further supported by the analysis of a series of a-LTX truncation mutants, lacking 1,2, 3, or 8 C-terminal ankyrin repeats (Li et al. 2005). When tested in NRX Ia-transfected tsA cells, some of these constructs induce cation conductance others completely lack this ability. As all these mutants possess unaltered N-terminal wing domains, the wing apparently does not participate in pore formation, while the structure of the C-terminal head is crucial for membrane insertion. This is consistent with the model of the membrane-inserted a-LTX tetramer in Figure 2. 

Here, A is the cell thickness, A is the equivalent conductivity of the salt solution, r is the area resistance, the superscripts d, c, am and cm refer to the diluate, the concentrate, and the anion- and the cation-exchange membranes, respectively. 

Here, fcdes and Edesspc are the desalination energy and the specific desalination, l is the total current, t is the time of operation Cfd and Cfc are the equivalent concentrations of the diluate and the concentrate at the cell inlet, C1 and C° are the concentrations ofthe diluate and the concentrate at the cell outlet, A is the equivalent conductivity of the salt solution, f" and rcm are the area resistances of the anion- and cation-exchange membrane, A is the cell thickness, is the current utilization, and is the diluate... 

So, since the conventional cationic exchange membranes suffer from higher S02 transport, CEA has built a test facility to characterise S02 transport through membranes. In collaboration with other laboratories, CEA is developing new membranes with reduced S02 transport characteristics and high ionic conductivity. 

Ion-exchange membrane is designed to allow the transport of primarily sodium ions and water from the anolyte to the catholyte compartment, whereas the diaphragm allows the percolation of all the anolyte through the separator. The cation-conducting, ion-exchange membrane is structured to reject anions, as indicated in Fig. 26.9. The chlor-alkali membranes in use today consist of one or more perfluorinated ion-exchange polymeric mate-... 

Diakov, A., Koch, J.R, Ducoudret, O., Muller-Berger, S., and Frbmter, E. 2001). The disulfonic stilbene DIDS and the marine poison maitotoxin activate the same two types of endogenous cation conductance in the cell membrane of Xenopus laevis oocytes. PflugersArch 442, 700-708. 

The last value can be lowered to 1300 kWh t-1, if the diaphragms are replaced by cation exchange membranes of the sulfonate type pretreated to conduct hydronium ions [3, p. 133]. 

Membrane electrolyzers for water decomposition use cation exchange membranes of the type used in the chlor-alkali membrane process, in this case made H+-ion conducting by different pretreatment. So, the ions generated at the anode (H2O -> 2H++ I/2O2 + 2e ) pass through the membrane and form at the cathode hydrogen (2H+ + 2e -> H2). 

---