Electrolyte membrane

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. 

Vandenborre Hv Leysen R., Baetsle L.H., Alkaline inorganic-membrane-electrolyte (IME) water electrolysis, bit.. Hydrogen Energ., 5(2), 165-171,1980. 

DEM (Dished Electrode Membrane) Electrolytic Inc., Union, N.Y., tJSA [76]... 

Narayanan, S., Surampudi, S., and Halpert, G., Direct liquid-feed fuel cell with membrane electrolyte and manufacturing thereof, US 5,945,231 (to California Institute of Technology), (August 31, 1999). 

Earlier, Gavach et al. studied the superselectivity of Nafion 125 sulfonate membranes in contact with aqueous NaCl solutions using the methods of zero-current membrane potential, electrolyte desorption kinetics into pure water, co-ion and counterion selfdiffusion fluxes, co-ion fluxes under a constant current, and membrane electrical conductance. Superselectivity refers to a condition where anion transport is very small relative to cation transport. The exclusion of the anions in these systems is much greater than that as predicted by simple Donnan equilibrium theory that involves the equality of chemical potentials of cations and anions across the membrane—electrolyte interface as well as the principle of electroneutrality. The results showed the importance of membrane swelling there is a loss of superselectivity, in that there is a decrease in the counterion/co-ion mobility, with greater swelling. 

Equation (4.19) can be used only when (4.20) is valid. In simple systems (rapid processes at the membrane/electrolyte interface and a simple diffusion potential in the membrane) the apparent selectivity coefficient is a function of theflj/flK ratio alone, whereas in more complicated systems it also depends on the activities of J and K. 

Nikolsky and coworkers [275-277] developed a theory of the electric potential at the membrane/electrolyte phase boundary for exchange between the cations in solutions and variously active sites in the membrane. They successfully explained, among other things, the origin of the inflection point on the depen-... 

Proton exchange membrane fuel cell (PEMFC) working at around 70 °C with a polymer membrane electrolyte, such as Nafion, which is a solid proton conductor (conducting by the H + cation). 

The first key component of a membrane fuel cell is the membrane electrolyte. Its central role lies in the separation of the two electrodes and the transport of ionic species (e.g. hydroxyl ion, OH , in an AEM), between them. In general, quaternary ammonium groups are used as anion-exchange groups in these materials. However, due to their low stability in highly alkaline media [43,44], only a few membranes have been evaluated for use as solid polymer electrolytes in alkaline fuel cells. 

This may work well if the process involves only electrically neutral species. However, when ions are discriminated on the basis of size, the partitioning process is affected by the Donnan potential. This potential, which we discuss more fully in Chapter 6, develops at the membrane/electrolyte interface. Another possibility is to discriminate on the basis of charge, as shown in Fig. 7.10 (see Chapter 7). Again, a porous barrier membrane is used, although here it would contain fixed, electrically charged moieties. When placed in front of the transducer, it rejects the like-charged species by electrostatic repulsion. In other words, it is a form of ion exchange membrane. 

Here the subscripts s and m denote solid (electrodes and current collectors) and membrane (electrolyte) respectively. Note that these two equations can be treated as only one equation with variable a and source terms. The R s are the volumetric transfer currents due to electrochemical reaction which are non-zero only in the catalyst layers and can be calculated from the Butler-Volmer equation for anode and cathode sides as ... 

Here subscripts a and c denote anode and cathode respectively, iref is the reference exchange current density, y is the concentration dependence exponent, [ ] and [ ]ref represent the local species concentration and its reference concentration, respectively. Anode transfer current, Ra, is the source in the electric potential equations at the anode/electrolyte interface with positive sign on membrane (electrolyte) side and negative sign on solid (anode) side. Similarly, near the cathode interface, the source on membrane (electrolyte) side is negative of the cathode transfer current, Rc and that on solid (cathode) side is positive of Rc. The activation over-potentials, in Equations (5.35) and (5.36) are given by... 

Eoutj and Emnj are the individual potential drops at each interface caused by the application of the first and second potential steps. Am / x1 and A f+ are the formal ion transfer potentials for the target ion X+ and for the membrane electrolyte cation R+, respectively, c + is the concentration of the membrane electrolyte cation, R+, and Dy1 and D)) are the diffusion coefficients of X+ in the membrane (M phase) and R+ in the inner aqueous solution (w2 phase), respectively. 

Fig. 1. Southern blotting. The procedure shown is the original method of Southern using capillary action to blot the DNA bands from the gel to the nitrocellulose membrane. Electrolytic transfer is now often used instead.

Direct methanol fuel cell (DMFC)—Polymer membrane electrolyte no fuel reformer is needed, because the catalyst draws the H2 directly from the liquid methanol. This design can be used for cellular phones and laptops. 

See color insert following page 140.) The process of electrolysis can use liquid or solid electrolyte. (a) Liquid electrolyte, (b) Solid polymer membrane electrolyte (SPE). 

Fig. 4.31 Ionic conductivities for candidate electrolyte ceramics. The arbitrary assumption that for a planar cell format a resistance of <15 gQm 2 is required places an upper limit on the permitted thickness of the electrolyte lower values of conductivity demand thinner membranes whilst higher values permit correspondingly thicker membranes. Electrolyte thicknesses greater than approximately 150/an are considered mechanically self-supporting. After B.C.H. Steele [11],...

Lovell K and Page N, 1997, Membrane Electrolyte Technology for Solid Polymer Euel Cells. In ETSU F/02/00110/REP, Cranfield University. 

Linkous, C.A. et al. Development of new proton exchange membrane electrolytes for water electrolysis at higher temperatures, Int J. Hydrogen Energy, 23, 525-529 (1998). 

The idea of using an ion-conductive polymeric membrane as a gas-electron barrier in a fuel cell was first conceived by William T. Grubb, Jr. (General Electric Company) in 1955. - In his classic patent, Grubb described the use of Amber-plex C-1, a cation exchange polymer membrane from Rohm and Haas, to build a prototype H2-air PEM fuel cell (known in those days as a solid-polymer electrolyte fuel cell). Today, the most widely used membrane electrolyte is DuPont s Nation... 

Figure 12.1 is a schematic view of a typical PEM fuel cell. A membrane electrode assembly (MEA) usually refers to a five-layer structure that includes an anode gas diffusion layer (GDL), an anode electrode layer, a membrane electrolyte, a cathode electrode layer, and a cathode GDL. Most recently, several MEA manufacturers started to include a set of membrane subgaskets as a part of their MEA packages. This is often referred to as a seven-layer MEA. In addition to acting as a gas and... 

As mentioned above, an anode serves as the HOR site in a H2/O2 fuel cell. As such, it must fulfill the following basic functional requirements (1) transport H2 to the catalyst sites, (2) catalyze the HOR process, (3) carry protons away from the reaction sites to the membrane electrolyte, (4) remove electrons from the anode, and (5) transfer heat in or out of the reaction zone. Water management is also an important consideration, as it is for all PEM fuel cell components. 

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