Electrode semipermeable

Silver [7440-22-4] Ag, as an active material in electrodes was first used by Volta, but the first intensive study using silver as a storage battery electrode was reported in 1889 (5) using silver oxide—iron and silver oxide—copper combinations. Work on silver oxide—cadmium followed. In the 1940s, the use of a semipermeable membrane combined with limited electrolyte was introduced by Andrir in the silver oxide—2inc storage battery. 

Silver—Zinc Separators. The basic separator material is a regenerated cellulose (unplastici2ed cellophane) which acts as a semipermeable membrane aHowiag ionic conduction through the separator and preventing the migration of active materials from one electrode to the other. 

The enzyme can be immobilized on the electrode by several techniques (53). The simplest method, first used in 1962, is to trap an enzyme solution between the electrode surface and a semipermeable membrane. Another technique is to immobilize the enzyme in a polymer gel such as polyacrylamide which is coated on the electrode surface. Very thin-membrane films can be obtained by electropolymerization techniques (49,54,55) using polypyrrole, polyindole, or polyphenylenediamine films, among others. These thin films (qv) offer the advantage of improved diffusion of substrate and product that... 

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, ... 

Three kinds of equilibrium potentials are distinguishable. A metal-ion potential exists if a metal and its ions are present in balanced phases, e.g., zinc and zinc ions at the anode of the Daniell element. A redox potential can be found if both phases exchange electrons and the electron exchange is in equilibrium for example, the normal hydrogen half-cell with an electron transfer between hydrogen and protons at the platinum electrode. In the case where a couple of different ions are present, of which only one can cross the phase boundary — a situation which may exist at a semiperme-able membrane — one obtains a so called membrane potential. Well-known examples are the sodium/potassium ion pumps in human cells. 

Carbon dioxide devices were originally developed by Severinghaus and Bradley (59) to measure the partial pressure of carbon dioxide in blood. This electrode, still in use today (in various automated systems for blood gas analysis), consists of an ordinary glass pH electrode covered by a carbon dioxide membrane, usually silicone, with an electrolyte (sodium bicarbonate-sodium chloride) solution entrapped between them (Figure 6-17). When carbon dioxide from the outer sample diffuses through the semipermeable membrane, it lowers the pH of the inner solution ... 

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. 

An ion-selective electrode contains a semipermeable membrane in contact with a reference solution on one side and a sample solution on the other side. The membrane will be permeable to either cations or anions and the transport of counter ions will be restricted by the membrane, and thus a separation of charge occurs at the interface. This is the Donnan potential (Fig. 5 a) and contains the analytically useful information. A concentration gradient will promote diffusion of ions within the membrane. If the ionic mobilities vary greatly, a charge separation occurs (Fig. 5 b) giving rise to what is called a diffusion potential. 

The history of glucose enzyme electrodes starts with the first device developed in 1962 by Clark and Lyons from the Children Hospital in Cincinnati [3], Their first device relied on a thin layer of GOx entrapped over an oxygen electrode (via a semipermeable dialysis membrane), and monitoring the oxygen consumed by the enzyme-catalyzed reaction ... 

If the electrodes are surrounded by a semipermeable membrane through which only oxygen can diffuse from the external solution, reduction of oxygen will take place. 

Specially designed electrodes in which the electrode tip is covered in a gel containing the appropriate oxidase are commercially available. A semipermeable membrane retaining the gel, and permitting oxygen diffusion, completes the assembly. 

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-... 

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 ... 

Many simple ions such as K+.Na+.Cl, and Ca are normally kept within a narrow range of concentrations in the body, and they must be monitored during critical care. Potentiometric sensors for ion, also called ion-selective electrodes or ISEs, utilize a membrane that is primarily semipermeable to one ionic species. The ionic species is used to generate a voltage that generally obeys the Nemst equation [cf. Section 3.1.3.2 and Eq. (3.24)]... 

The combined effects of electroneutrality and the Donnan equilibrium permits us to evaluate the distribution of simple ions across a semipermeable membrane. If electrodes reversible to either the M+ or the X ions were introduced to both sides of the membrane, there would be no potential difference between them the system is at equilibrium and the ion activity is the same in both compartments. However, if calomel reference electrodes are also introduced into each compartment in addition to the reversible electrodes, then a potential difference will be observed between the two reference electrodes. This potential, called the membrane potential, reflects the fact that the membrane must be polarized because of the macroions on one side. It might be noted that polarized membranes abound in living systems, but the polarization there is thought to be primarily due to differences in ionic mobilities for different solutes rather than the sort of mechanism that we have been discussing. We return to a more detailed discussion of the electrochemistry of colloidal systems in Chapter 11. 

When using an amperometric electrode as the measuring technique, interference from the solutes and solvent can occur. The solutes and solvent can adsorb to the semipermeable membrane of the electrode, therefore giving an additional resistance to the diffusion of ozone through this membrane to the electrolyte chamber. The use of an amperometric electrode is not recommended for water containing particles. In these cases the ozone consumption can only be calculated from the ozone gas balance. 

DIALYSIS. The process of separating compounds or materials by the difference in their rates of diffusion through a colloidal sentipermeahle membrane. Thus, sodium chloride diffuses eleven limes as last as tannin ami twemy-une times as fast as albumin. When the process is conducted under the influence of a difference in electrical potential, as from electrodes on opposite sides of the semipermeable membrane, it is called clectrodialysis. 

For laboratory-scale reactions, this electrocatalytic AD generally is performed in a glass H-type cell in which the anode and cathode compartments are separated by a semipermeable Nafion cation-exchange membrane and platinum electrodes are used. A 5% aqueous solution of phosphoric acid is used in the cathode compartment, and the reaction in the anode compartment is stirred vigorously, Under a controlled anode potential of 0.4 V (vs. Ag/AgCl) and with (DHQD)2-PHAL as chiral ligand, a-methylstyrene was converted to 7 -2-pheny 1-1,2-propanediol in 15 h with the electrical consumption of 2.1 F/mol. The product was isolated in 100% yield with 92% ee [ 37],... 

In the previous papers(12,13), we reported on the vessel access type, i.e. tubular type, glucose sensor. It consisted of a glucose electrode system with a GOX enzyme immobilized Nylon membrane and a glucose semipermeable membrane, and a reference oxygen electrode system. The sensor could directly measure up to 700 mg/dl of BGL in an arterial blood stream when it was placed into an external A-V shunt. This sensor, however, has some problems such as thrombus during in vivo testing without heparin and clinical complexity associated with implanting the sensor in a blood stream. 

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 ... 

The electropolymerization of the semipermeable membrane can be performed on the Pt electrodes on a wafer as well as the photopatterning of the enzyme mem-... 

Thus, under equilibrium conditions, the emf of the double electrode-pair system is determined solely by electric potential differences developed at the two liquid junctions that involve KC1 salt bridges. The two Ej may differ because of the effect of soil colloids. Thus the fact that this emf can develop is known as the suspension effect.40 Only ionic transport processes across the liquid junctions need be taken into account in order to evaluate E. Ionic transport processes across the semipermeable membrane between the suspension and the solution are not germane. Moreover, since neither Ej nor Ej can be calculated by strictly thermodynamic methods, the interpretation of E must be made in terms of specific models of ionic transport across salt bridges contacting suspensions and solutions. Thus the relation between E and the behavior of ions in soil suspensions is not direct. 

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. 

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