Membranes conductance

A potential developing across a conductive membrane whose opposite sides are in contact with solutions of different composition. 

Later, Du Pont in America developed its own ionically conducting membrane, mainly for large-scale electrolysis of sodium chloride to manufacture chlorine, Nafion , (the US Navy also used it on board submarines to generate oxygen by electrolysis of water), while Dow Chemical, also in America, developed its own even more efficient version in the 1980s, while another version will be described below in connection with fuel cells. Meanwhile, Fenton et al. (1973) discovered the first of a... 

Ren, X. Springer, T. E. and Gottesfeld, S. (1998). Direct Methanol Fuel Cell Transport Properties of the Polymer Electrolyte Membrane and Cell Performance. Vol. 98-27. Proc. 2nd International Symposium on Proton Conducting Membrane Euel Cells. Pennington, NJ Electrochemical Society. 

The principal cathodic reaction on the upper surface of the membrane is the reduction of Cu " that is formed by the reaction of Cu with dissolved oxygen in the water these Cu ions are provided partly from the diffusion through the pores in the oxide membrane from within the pit and partly from those produced by cathodic reduction (equation 1.154). Lucey s theory thus rejects the conventional large cathode small anode relationship that is invoked to explain localised attack, and this concept of an electronically conducting membrane has also been used by Evans to explain localised attack on steel due to a discontinuous film of magnetite. 

B.C.H. Steele. Dense Ceramic ion conducting membranes in Oxygen ion and mixed conductors and their technological applications, (1997) Erice, Italy Kluwer. 

A fuel cell consists of an ion-conducting membrane (electrolyte) and two porous catalyst layers (electrodes) in contact with the membrane on either side. The hydrogen oxidation reaction at the anode of the fuel cell yields electrons, which are transported through an external circuit to reach the cathode. At the cathode, electrons are consumed in the oxygen reduction reaction. The circuit is completed by permeation of ions through the membrane. 

Figure 15. Extent of methanol crossover through different ETFE proton-conducting membranes. Comparison with the behavior ofNafion 117 ( ).

Apart from the problems of low electrocatalytic activity of the methanol electrode and poisoning of the electrocatalyst by adsorbed intermediates, an overwhelming problem is the migration of the methanol from the anode to the cathode via the proton-conducting membrane. The perfluoro-sulfonic acid membrane contains about 30% of water by weight, which is essential for achieving the desired conductivity. The proton conduction occurs by a mechanism (proton hopping process) similar to what occurs... 

S. R. Narayanan, A. Kindler, B. Jeffries-Nakamura, W. Chun, H. Frank, M. Smart, S. Surampudi, and G. Halpert, in Proc. of the First International Symposium on Proton Conducting Membrane Fuel Cells, Ed. by S. Gottesfield, G. Halpert, and A. R. Landgrebe, The Electrochemical Society, Pennington, NJ, PV 95-23, 1995, pp. 261-266. 

This type of electrolytic cell consists of anodes and cathodes that are separated by a water impermeable ion-conducting membrane. Brine is fed through the anode where chlorine gas is generated and sodium hydroxide solution collects at the cathode. Chloride ions are prevented from migrating from the anode compartment to the cathode compartment by the membrane and this, consequently, leads to the production of sodium hydroxide, free of contaminants like salts. The condition of the membrane during operation requires more care. They must remain stable while being exposed to chlorine and strong caustic solution on either side they must allow, also, the transport of sodium ions and not chloride ions. 

The PEMFCs require expensive polymer membrane (e.g., Nation ), and operate at a low temperature (e.g., 80°C). Although low temperature reduced the cost of material, the heat generated at low temperatures is more difficult to remove. Alternate proton conducting membranes (e.g., inorganic polymer composites) that will operate at a high temperature (e.g., 200°C) are required. The expensive platinum catalyst used for electrochemical reactions can be poisoned by even trace amounts of carbon monoxide in the hydrogen fuel stream. Hence, a more tolerant catalyst material needs to be developed. 

Elangovan, S., B. Nair, J. Hartvigsen, and T. Small, Mixed Conducting Membranes for Pressure Driven Hydrogen Separation from Syngas, 225th American Chemical Society National Meeting, Fuels Division, New Orleans, LA, March 2003. 

Lackner, K.S., West, A.C., and Wade, J.L., Ion Conducting Membranes for Separation of Molecules, U.S. Patent Publication Number WO2006113674, 2006. 

In the recent years, many researchers have devoted attention to the development of membrane science and technology. Different important types of membranes, such as these for nanofiltration, ultrafiltration, microfiltration, separation of gases and inorganic membranes, facilitated or liquid membranes, catalytic and conducting membranes, and their applications and processes, such as wastewater purification and bio-processing have been developed [303], In fact, almost 40 % of the sales from membrane production market are for purifying wastewaters. 

GDE s may be interesting for synthesis cells as depolarized electrodes (e.g. [48]). A hydrogen-consuming anode will work at a low potential that avoids undesired anodic oxidations (e.g. no chlorine evolution in presence of chlorides). In order to reject an excess of the electrolyte from the GDE structure, a proton-conducting membrane (Nafion ) between the GDE and the electrolyte can be used ( Hydrina , De Nora Spa. [49]). 

A.R. Landgrebe, S. Gottesfeld, First International Symposium on Proton Conducting Membrane Fuel Cells, Chicago, h. Proceedings Vol. 95-23, The Electrochemical Society, Inc., Pennington, N.J., 1995. 

Kreuer, K. D. 2001. On the development of proton conducting membranes for hydrogen and methanol fuel cells. Journal of Membrane Science 185 29-39. 

Zhang, L., Ma, C. and Mukerjee, S. 2004. Oxygen reduction and transport characteristics at a platinum and alternative proton conducting membrane interface. Journal of Electroanalytical Chemistry 568 273-291. 

Hiibner, G. and Roduner, E. 1999. EPR investigation of HO radical initiated degradation reactions of sulfonated aromatics as model compounds for fuel cell proton conducting membranes. Journal of Materials Chemistry 9 409- 18. 

Nolte, R., Ledjeff, K., Bauer, M. and Miilhaupt, R. 1993. Partially sulfoanted PAES—A versatile proton conducting membrane material for modern energy conversion technologies. Journal of Membrane Science 83 211-220. 

Asano, N., Aoki, M., Suzuki, S., Miyatake, K., Uchida, H. and Watanabe, M. 2006. Aliphatic/aromatic polyimide ionomers as a proton conductive membrane for fuel cell applications. Journal of the American Chemical Society 128 1762-1769. 

Jeske, M., Soltmann, C., Ellenberg, C., Wilhelm, M., Koch, D. and Grathwohl, G. 2007. Proton conducting membranes for the high temperature-polymer electrolyte membrane-fuel cell (HT-PEMFC) based on functionalized polysiloxanes. 

Edmondson, C. A., Eontanella, J. J., Chung, S. H., Greenbaum, S. G. and Wnek, G. E. 2001. Complex impedance studies of S-SEBS block polymer proton-conducting membranes. Electrochimica Acta 46 1623-1628. 

Deimede, V. A. and Kallitsis, J. K. 2005. Synthesis of polyjarylene ether) copolymers containing pendant PEO groups and evaluation of their blends as proton conductive membranes. Macromolecules 38 9594—9601. 

Code, P, Hult, A., Jannasch, P, Johansson, M., Karlsson, L. E., Lindbergh, G., Malmstrom, E. and Sandquist, D. 2006. A novel sulfonated dendritic polymer as the acidic component in proton conducting membranes. Solid State Ionics 177 787-794. 

Haute, S. and Stimming, U. 2001. Proton conducting membranes based on electrolyte filled microporous matrices. Journal of Membrane Science 185 95-103. 

Allcock, H. R., Hofmann, M. A., Ambler, C. M., Lvov, S. N., Zhou, X. Y., Chalkova, E. and Weston, J. 2002. Phenyl phosphonic functionalized poly(aryloxyphosphanes) as proton-conducting membranes for direct methanol fuel cells. Journal of Membrane Science 201 47-54. 

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