Membrane electrolizer

In membrane electrol sis an electrolysis process is combined w ilh a membrane separation process. The classical example is the chlor-alkali process in which sodium chloride is converted into chlorine and caustic soda. Other examples are the electrolytic recovery of (hea 7) metals and the production of acid and base from the corresponding salts. 

Diard J-P. 1998. Impedance measurements of polymer electrol)4e membrane fuel cells running on constant load. J Power Sources 74 244-245. 

Finally, electrodialysis may be mentioned, a process widely used to de-salt aqueous solutions. An electric field is applied across a stack of alternating cation-exchange and anion-exchange membranes. Ions in the electrolyte solutions between these membranes are transported till they meet a membrane of the same sign, so that electrolyte-rich and electrol)rte-freed solutions are created. The process involves conduction and electro-osmosis. Obviously, irreversible thermod mamics appears very suitable to describe the various flows... 

F.N. Buchi, B. Gupta, O. Haas, and G.G. Scherer. Study of radiation-grafted FEP-g-polystyrene membranes as polymer electrol)des in fuel-cells. Electrochimica Acta 40, 345-353 1995. 

Velocity profiles across the capillary have a Poisseuille shaped flow and the expression predicts that the electroosmotic coefficient of permeability should vary with the square of the radius. In practice, it is found generally that this law is not as satisfactory as the Helmholtz-Smoluchowski approach for predicting electroosmotic behavior in soils. The failure of small pore theory may be because most clays have an aggregate structure with the flow determined by the larger pores [6], Another theoretical approach is referred to as the Spiegler Friction theory [25,6]. Its assumption, that the medium for electroosmosis is a perfect permselective membrane, is obviously not valid for soils, where the pore fluid comprises dilute electrol d e. An expression is derived for the net electroosmotic flow, Q, in moles/Faraday,... 

Modeling the State of the Water in Polymer Electrol h e Membranes 375... 

Paddison, S. J. Proton conduction mechanisms at low degrees of hydration in sulfonic acid-based polymer electrol de membranes. Ann. Rev. Mat. Res. 2003, 33, 289-319. 

Donnan, F.G., Theory of membrane equilibria and membrane potentials in the presence of nondialysing electrol 4es. A contribution to physical-chemical physiology. J. Membr. Sci, 100, 45-55, 1995. 

Although a variety of different anode-cathode combinations for oxygen electrode are available, the platinum with silver/silver chloride is the most used cathode-anode combination. The often found arrangement of these electrodes is annular with the tubular silver/silver chloride anode enclosing the platinum cathode. The electrodes dip into an electrol)de solution (usually a buffered potassium chloride solution) which is held inside an electrode by an ojqrgen permeable membrane. The membrane might be a very thin polypropylene. Polarization of electrodes at 0.6 V is achieved with the help of a mercury cell. 

Figure 19.9. Polarization curves and the corresponding power density curves of fuel cells with a Pt/C/Nafion-PTFE/C eatalyst cathode and a Pt/C/Nafion membrane-based cathode, respectively. Measured at 80 °C. The hydrogen and air reactant gases were externally humidified at 90 °C and 85 °C, respectively. The flow rates were 50 mL min for hydrogen and 200 mL min for air [49]. (Reprinted from Eleetroehemistry Communications, 8(7), Tian ZQ, Wang XL, Zhang HM, Yi BL, Jiang SP, Microwave-assisted sjmthesis of PTFE/C nanocomposite for polymer electrol)4e fuel cells, 1158-62, 2006, with permission from Elsevier.)...

Figure 22.9. Schematic planar representation of the cataljhic layer [81] (A) at low Nafion content, not all the catalyst particles are connected to the membrane hy a Nafion bridge (C) when there is too much Nafion not all the catalyst particles are electronically connected to the diffusion layer (B) at the optimal Nafion content all the catalyst particles have good connections for ionic and electronic conduction. (Reprinted from Electrochimica Acta, 46(6), Passalacqua E, Lufrano F, Squadrito G, Patti A, Giorgi L. Nafion content in the catalyst layer of polymer electrol)de fuel cells effects on structure and performance, 799-805, 2001, with permission from Elsevier.)...

Finally we come to the fuel cell itself. In addition to the original Grove fuel ceU and the alkaline and phosphoric acid fuel cells used in space technology, other types of ceU include the molten carbonate fuel ceU (with a molten Li2C03/Na2C03 electrol 4e), the soUd oxide fuel ceU (containing a sohd metal oxide electrol 4e) and the polymer electrolyte membrane (PEM) fuel cell. Both the molten carbonate and soUd oxide fuel cells... 

Figure I.6a also reveals the timeline of milestones in fuel cell design. The leftmost curve is the performance curve of the first practical H2/O2 fuel cell, built by Mond and Langer in 1889 (Mond and Langer, 1889). The electrodes consisted of thin porous leafs of Pt covered with Pt black particles with sizes of 0.1 lam. The electrol)de was a porous ceramic material, earthenware, that was soaked in sulfuric acid. The Pt loading was 2 mg cm and the current density achieved was about 0.02 A cm at a fuel cell voltage of 0.6 V. The next curve in Figure I.6a marks the birth of the PEFC, conceived by Grubb and Niedrach (Grubb and Niedrach, 1960). In this cell, a sulfonated cross-linked polystyrene membrane served as gas separator and proton conductor. However, the proton conductivity of the polystyrene PEM was too low and the membrane lifetime was too short for a wider use of this cell. It needed the invention of a new class of polymer electrolytes in the form of Nafion PFSA-type PEMs to overcome these limitations.

Carbon materials, such as carbon cloth and carbon paper, are also good substrates for the deposition of photocatalysts, due to their low resistivity and cost. They are also widely used in the proton exchange membrane fuel cell (PEMFC), and are also commercially available at www.fuelcellstore.com. Carbon cloth/paper is supplied with an untreated surface or reinforced with PTFE. Since the photocatal5ftic reactions at the anode side involve three phases liquid electrol)4e, solid anode photocatalyst, and the produced gaseous CO2, carbon materials with hydrophilic surfaces are preferred in the fabrication of photoanodes. Compared to the previous two substrates, carbon material can be used directly without any pretreatment. 

Bae J.M., Honma I., Hirakawa S. Synthesis and properties of ceramics-polymer composite membranes as high temperature proton conducting electrol)des. J. Korean Phys. Soc. 1999 35 315-319... 

J. Kerres, A. Ullrich, M. Hein, V. Gogel, K. A, Friedrich, and L. Jorissen, Cross-linked polyaryl blend membranes for polymer electrol 4e fuel cells. Fuel Cells 4(1-2), 105-112... 

Nouel, K.M., Fedkiw, P.S. (1998) Nafion -based composite polymer electrol) te membranes. Electrochimica Acta, 4, 2381-2387. 

Peron, J., Ruiz, E., Jones, D.J., Roziere, J. (2008) Solution sulfonation of a novel polybenzintidazole a proton electrol) te for fuel cell application. Journal of Membrane Science, 314, 247-256. 

This may be achieved by determining the charactereristics of the lithium intercalation-deintercalation processes of these materials in ceUs based on the given membrane as the electrol and lithium metal as the counter electrode. 

The vesicle assay previously used ves a good survey of transporter activity under a fixed set of conditions. However it is not suited to exploration of transport activity as a function of the sign and magmtude of the transmembrane potential. Bilayer conductance, or single channel recording techniques are required (21). In this techmque, a lipid bilayer is formed across a small hole in a Teflon barrier, by direct application of the lipid in decane to the hole. Under favorable conditions, Ae lipid tl s to a bilayer membrane which electrically isolates the two halves of the cell. T icdly KCl is used as an electrol, and electrical contact is made via Ag/AgQ wires directly inserted into the solutions. A high impedance operational amplifier circuit (bUayer clamp) can then be used to apply a fixed transmembrane potential and to monitor the current which flows as a function of time. The two sides of the membrane are independently accessible, so different sequences of transporter addition, control of pH, and other variables are in principle j ssible. 

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