Semipermeability, electrochemical

The discovery of galvanic electricity (i.e. electrical phenomena connected with the passage of electric current) by L. Galvani in 1786 occurred simultaneously with his study of a bioelectrochemical phenomenon which was the response of excitable tissue to an electric impulse. E. du Bois-Reymond found in 1849 that such electrical phenomena occur at the surface of the tissue, but it was not until almost half a century later that W. Ostwald demonstrated that the site of these processes are electrochemical semipermeable membranes. In the next decade, research on semipermeable membranes progressed in two directions—in the search for models of biological membranes and in the study of actual biological membranes. 

Yttria stabilized zirconia formed by this reaction fills the air electrode pores. The dynamics of this CVD stage has been modeled by Carolan and Michaels [120], who observed that films produced in this manner penetrate the substrate no more than 2-3 pore diameters from the chloride face of the substrate. It has also been shown that the penetration depth is independent of water concentration. The second step of this method is the EVD step. Once pore closure is achieved, the reactants are not longer in contact. Electrochemical semipermeability related to the existence of small electronic conductivity and large gradient of oxygen partial pressure leads to oxygen transport from the steam side to the chloride side through the deposited electrolyte. The electrochemical reactions involved are ... 

J. Fouletier, P. Fabry and M. Kleitz, Electrochemical semipermeability and the elctrode microsystem in solid oxide electrolyte cells. /. Electrochem. Soc., 123(2) (1976) 204-213. 

The Fermi level gradient shown in Fig.5 results in a microelectronic current which is compensated by an equivalent microionic current. This is the so-called electrochemical semipermeability phenomenon. ... 

Electrodecantation or electroconvec tion is one of several operations in which one mobile component (or several) is to be separated out from less mobile or immobile ones. The mixture is introduced between two vertical semipermeable membranes for separating cations, anion membranes are used, and vice versa. When an electric field is apphed, the charged component migrates to one or another of the membranes but since it cannot penetrate the membrane, it accumulates at the surface to form a dense concentrated layer of particles which will sink toward the bottom of the apparatus. Near the top of the apparatus immobile components will be relatively pure. Murphy [J. Electrochem. Soc., 97(11), 405 (1950)] has used silver-silver chloride electrodes in place of membranes. Frilette [J. Phys. Chem., 61, 168 (1957)], using anion membranes, partially separated and Na, ... 

Surface-modified electrodes were used for prevention of high overpotentials with direct oxidation or reduction of the cofactor, electrode fouling, and dimerization of the cofactor [7cj. Membrane electrochemical reactors were designed. The regeneration of the cofactor NADH was ensured electrochemically, using a rhodium complex as electrochemical mediator. A semipermeable membrane (dialysis or ultrafiltration) was integrated in the filter-press electrochemical reactor to confine... 

Among electrochemical methods of water purification, one can also list the various electromembrane technologies, electrodialysis in particular. The simplest elec-trodialyzer consists of three compartments separated by semipermeable membranes (usually, cation- and anion-exchange membranes). The water to be purified is supplied to the central (desalination) compartment. In the outer (concentration) compartments, electrodes are set up between which a certain potential difference is applied. Under the effect of the electric field, ions pass througfi the membranes so that the concentration of ionic contaminants in the central compartment decreases. 

In each of the SILVER II cells, a pair of electrodes (anode and cathode) is housed in a compartment within the cell. A semipermeable membrane is placed between the electrodes. The membrane maintains electrical continuity between the electrodes and prevents mixing of the anolyte and catholyte solutions. The electrochemical cells operate at 190°F and essentially at-... 

The movement of solute across a semipermeable membrane depends upon the chemical concentration gradient and the electrical gradient. Movement occurs down the concentration gradient until a significant opposing electrical potential has developed. This prevents further movement of ions and the Gibbs-Donnan equilibrium is reached. This is electrochemical equilibrium and the potential difference across the cell is the equilibrium potential. It can be calculated using the Nemst equation. 

Electrochemical Reactions. Consider a simple galvanic cell, composed of two metal electrodes, zinc and copper, immersed in two different aqueous solutions of unit activity—in this case, 1.0 M ZnS04 and 1.0 M CUSO4, respectively, connected by an electrical circuit, and separated by a semipermeable membrane (see Figure 3.8). The membrane allows passage of ions, but not bulk flow of the aqueous solutions from one side of the cell to the other. Electrons are liberated at the anode by the oxidation (increase in the oxidation number) of the zinc electrode ... 

Divided cells — Electrochemical cells divided by sintered glass, ceramics, or ion-exchange membrane (e.g., - Nafion) into two or three compartments. The semipermeable separators should avoid mixing of anolyte and - catholyte and/or to isolate the reference electrode from the studied solution, but simultaneously maintain the cell resistance as low as possible. The two- or three-compartment cells are typically used a) for preparative electrolytic experiments to prevent mixing of products and intermediates of anodic and cathodic reactions, respectively b) for experiments where different composition of the solution should be used for anodic and cathodic compartment c) when a component of the reference electrode (e.g., water, halide ions etc.) may interfere with the studied compounds or with the electrode. For very sensitive systems additional bridge compartments can be added. 

Diaphragm cell A family of electrochemical chlor-alkali processes using cells with semiperme-able membranes that minimize diffusion between the electrodes. The overall reaction is... 

An enzyme electrode consists of an electrochemical sensor to which a thin layer of enzyme is attached (Fig. 2). Generally, a semipermeable membrane is fixed between the enzyme layer and the solution, between the enzyme layer and the elearode, or both. The resulting probe can operate without pretreatment of the sample since accuracy is achieved independendy of the color and turbidity of the solution. 

Lin Y.S., de Vries K.J., Brinkman H.W. and Buiggraaf A.J., Oxygen semipermeable solid oxide membrane composites prepared by electrochemical vapor deposition, 7. Membr. ScL 66 211 (1992). 

Electrocbemical systems consisting of two parts where one or more charged species is restricted to one part of the system by a semipermeable membrane were first investigated by Donnan in the early twentieth century. In such systems, the equilibrium condition for all solute species is that their electrochemical potentials are equal on both sides of the membrane ... 

Y.S. Lin, K.J. de Vries, H.W. Brinkman and A.J. Burggraaf, Oxygen semipermeable solid oxid membrane composites prepared by electrochemical vapor deposition. J. Membr. Sci, 66 (1992) 211-226. 

G.Z. Cao, Electrical conductivity and oxygen semipermeability of terbia and yttria stabilized zirconia. /. Appl. Electrochem., 24 (1994) 1222-1224. 

The most widely employed types of biosensors are those that employ an oxidase to generate hydrogen peroxide. A classic example is the electrode containing an immobilized glucose oxidase that generates an amperometric signal related to the concentration of glucose present in the sample. However, biosensors of these types are often susceptible to interference from other electrochemically active solutes in the sample. A wide variety of techniques have been developed to circumvent or minimize this problem, for example, application of a semipermeable membrane above the... 

Sorkin, M., Kaufman, A., Gibbard, H.F., and Barton, S.C. (2008) Methanol anode modified by semipermeable membrane for mixed-feed direct methanol fuel cells. Journal of the Electrochemical Society, 155 (9), B865-B868. 

In biospecific electrodes the eliminating enzymes are directly integrated in the sensor in membrane-immobilized form and separated from the indicator enzyme layer by a semipermeable membrane. The first enzymatic anti-interference layer was developed to enable the electrochemical determination of catecholamines in brain tissue at a graphite... 

The electrochemical gradient across a semipermeable membrane determines the direction of ion movement through channel proteins. The two forces constituting the electrochemical gradient, the membrane electric potential and the ion concentration gradient, may act in the same or opposite directions (see Figure 7-20). 

Fluorescence quenching of dyes in semipermeable membranes Electrochemical... 

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