Electro-conducting membrane

In this section, additives for cathodes are reported by categorizing them into (1) sulfur-containing compounds with active site poisoning function [105-107] and (2) aromatic compounds forming an electro-conducting membrane (ECM) [2,109,110]. 

Aromatic Compounds Forming an Electro-Conducting Membrane... 

Linkov V. New inorganic proton-conducting membranes for hydrogen separation and electro-catalysis. Membr. Technol. 2001 132 4-8. 

M. Eikerling, Y.l. Kharkats, A.A. Komyshev, and Y.M. Volfkovich. Phenomenological theory of electro-osmotic effect and water management in polymer electrolyte proton-conducting membranes. Journal of the Electrochemical Society 145, 2684—2699 1998. 

Since then, other colloidal oxide systems have been investigated in order to prepare ceramic mesoporous membranes designed for ultrafiltration. The preparation of an electronically conductive membrane from a Ru02 Ti02 mixed oxides sol and the application to an electro-ultrafiltration process [25,26], as well as the preparation of titania and zirconia ultrafiltration membranes [27], have been described following a colloidal process in which a partial destabilization of a metal oxide colloidal suspension is used to produce top layers with different pore size and pore volume in the mesoporous range. In agreement... 

With regard to substrate-selective sensors with pre-organized cavities, impressive advances have been made in molecular imprinting [55-57]. The discovery of MIP-membrane electro conductivity was an interesting issue, which actually led to the appearance of the earliest MIP sensors [58,59]. It was shown that the membrane electroconductivity could be a function of the interaction between MIP-membrane and ligand (i.e., imprint species) (Fig. 5). An increase in the ligand concentration would result in an enhancement of membrane conductivity. With the same level of concentration, a maximal electro conductivity with the imprint species could be achieved. In addition, it has also been confirmed that polymers imprinted with amino acids, nucleosides, atrazines, sialic acids, or cholesterols can show similar features if coupled with the appropriate transducer [60-64], In particular, molecular imprinting is presently probably the only choice when no suit-... 

Stream would not rupture them. The membranes are essentially water impermeable and very thin (0.5 mm) so diffusion and exchange are fast, as is electro-conductivity. Pore sizes vary from 10 to 100 A with 10 to 20 A being more common. They have a capacity of from... 

The vast catalogue of polymeric materials reviewed here included Nafion composite with inorganic and organic fillers, and non-fluorinated proton conducting membranes such as sulfonated polyimides, poly(arylene ether)s, polysulfones, poly (vinyl alcohol), polystyrenes, and acid-doped polybenzimidazoles. Anion-exchange membranes are also discussed because of the facile electro-oxidation of alcohols in alkaline media and because of the minimizatirHi of alcohol crossover in alkaline direct alcohol fuel cells. 

Irradiated PVDF and poly(VDF-co-TrFE) copolymer possess ferroelectric properties that allow the use of such fluorinated polymer in the domain of captors, sensors, and detectors [47,194]. Another interesting property of crosslinked poly(VDF-co-HFP) copolymer is their insolubihty in organic solvent [195]. Cured fluorinated polymers can be processed as membranes for many electrochemical applications such as fuel cell and batteries [196]. For example, a poly(VDF-co-HFP) copolymer has been crossUnked with various systems such as polyols [197], by irradiation with electron beam or y-rays [197] or with aliphatic amines [198] in order to elaborate a solid polymer electrolyte for non aqueous lithium battery [197,198]. This electrolyte is particularly interesting for its ionic conductivity, its adhesion with an electro-conductive substrate and also remarkably enhanced heat resistance. 

S. Yabuki. H. Shinohara, and M. Aizawa, Electro-conductive enzyme membranes, J. Chem. Soc., Chem. Commun. 945 (1989). 

Hu, J., Luo, J., Wagner, P., Conrad, O., and Agert, C. (2009) Anhydrous proton conducting membranes based on electro-deficient nanoparticles/PBI-OO/PFSA blend composites for high temperature PEMFC, Electrochem. Comm., 11, 2324-2327. 

The main components of a PEM fuel cell are the flow channels, gas diffusion layers, catalyst layers, and the electrolyte membrane. The respective electrodes are attached on opposing sides of the electrolyte membrane. Both electrodes are covered with diffusion layers, and the flow channels/current collectors. The flow channels collect current from the electrodes while providing the fuel or oxidant with access to the electrodes. The gas diffusion layer allows gases to diffuse to the electro-catalysts and provides electrical contact throughout the catalyst layers. Within the anode catalyst layer, the fuel (typically H2) is oxidized to produce electrons and protons. The electrons travel through an external circuit to produce electricity, while the protons pass through the proton conducting electrolyte membrane. Within the cathode catalyst layer, the electrons and protons recombine with the oxidant (usually 02) to produce water. 

MeOH is transported through the membrane by two modes diffusion and electro-osmotic drag. ° When MeOH comes into contact with the membrane, it diffuses through the membrane from anode to cathode and is also dragged along with the hydrated protons under the influence of current flowing across the cell. Therefore, a correlation between the MeOH diffusion coefficient and proton conductivity is observed. The diffusive mode of MeOH transport dominates when the cell is idle, whereas the electro-osmotic drag... 

Continuity of fhe wafer flux fhrough the membrane and across the external membrane interfaces determines gradients in water activity or concentration these depend on rates of water transport through the membrane by diffusion, hydraulic permeation, and electro-osmofic drag, as well as on the rates of interfacial kinetic processes (i.e., vaporization and condensafion). This applies to membrane operation in a working fuel cell as well as to ex situ membrane measuremenfs wifh controlled water fluxes fhat are conducted in order to study transport properties of membranes. 

The physical mechanism of membrane water balance and the formal structure of modeling approaches are straightforward. Under stationary operation, the inevitable electro-osmotic flux has to be compensated by a back flux of water from cathode to anode, driven by gradients in concentration, activity, or liquid pressure of water. The water distribution in PEMs that is generated in response to these driving forces decreases from cathode to anode. With increasing/o, the water distribution becomes more nonuniform. the water content near the anode falls below the percolation threshold of proton conduction, X < X. This leaves only a small conductivity due to surface transport of water. As a consequence, increases dramatically this can lead to failure of the complete cell. 

Guizard C F. Legault, N. Idrissi, A. Larbot, L. Cot and G. Gavach. 1989. Electronically conductive mineral membranes designed for electro-ultrafiltration. J. Membrane Science 41 127-142. 

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