Electrode Processes

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Electrode Processes


electrochemical conversions that occur at an electrode-electrolyte interface where a charge is transferred through the interface and an electric current flows. Depending on the direction of the electron flow (from the electrode to the material or vice versa) a distinction is made between cathodic and anodic processes, which result in the reduction and oxidation, respectively, of the material. The spatial separation of the oxidation and reduction processes is used in chemical sources of electric current and for electrolysis.

The current density (in amperes per cm2) serves as a precise measure of the rate of an electrode process, which depends on the electrode potential, the structure of the electric double layer, and the presence of adsorbed particles at the phase interface. The rate increases as the overvoltage rises. At the equilibrium potential a dynamic equilibrium is achieved: current does not flow through the electrode, but there is a continuous exchange of charge carriers, that is, ions and electrons, across the phase interface; this exchange current is one of the principal kinetic parameters of electrode processes. The rate may vary within extremely wide limits depending on the nature of the electrode. Thus, the exchange current in the electrochemical process of evolving hydrogen from aqueous solutions of acids ranges from 10–12 ampere per cm2 for a mercury electrode to 0.1 ampere per cm2 for a platinum electrode. The concentration of reactive particles and the temperature also affect the rate.

The simplest electrode processes are electron-transfer reactions of the type Fe2+ → Fe3+ + e. The electron transfer may be accompanied by the breaking of chemical bonds and the transfer of atoms from the original material to the product of the reaction, as in the case C6H5NO2 + 6H+ + 6e → C6H5NH2 + 2H2O. In more complex electrode processes a new phase is formed. Such processes include cathodic deposition and anodic dissolution of metals (such as Λg+ + e → Ag) and the evolution and ionization of gases (for example, 2H+ + 2e ⇄ H2). One of the stages of an electrode process is always the discharge-ionization stage—the transfer of a charged particle across the phase interface—which constitutes the elementary electrochemical event of the overall process. Electrode processes also include a stage in which a reactive material is delivered to the surface of an electrode and a stage in which the products of the reaction are distributed throughout the solution. They may also include chemical stages that precede or follow the discharge-ionization stage. (SeeELECTROPLATING TECHNOLOGY, , and for descriptions of electrode processes widely used in technology.)


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
A linear relationship between the oxidation potential [E.sub.p] and lnv has been observed, confirming totally irreversible electrode processes:
The most expensive components of the cell with a solid electrolyte are proton exchange membrane and catalysts of electrode processes. The most used catalysts are platinum-group metals (platinum, palladium, iridium and ruthenium) in the form of nanoscale particles and their oxides.
"The images are unique and help us to develop theories to better describe the electrode processes in ionic liquids", says physicist Magnussen.
They cover fundamentals of electrochemistry dealing with organic molecules, methods for studying organic electrochemistry: electrochemical measurements of organic molecules, methods for organic electrosynthesis, organic electrode reactions, organic electrosynthesis, a new methodology of organic electrochemical synthesis, related fields of organic electrochemistry, and examples of commercialized organic electrode processes. ([umlaut] Ringgold, Inc., Portland, OR)
Heterogeneous electrode processes and localized corrosion.
The electrode processes were simulated with sequence of reaction as presented in scheme 3.
In order to stimulate electrode processes the concrete samples were immersed in tap water to half the depth of the reinforcement for 24 hours before the impedance measurements.
In five chapters, the authors cover the thermodynamics of irreversible processes (including balance equations), transport equations (including the Fickian, Nernst-Planck and Stefan-Maxwell approaches), transport and electrodes (including electrode processes in stationery states, hydrodynamic electrodes, and non-stationary or transient electrode processes), transport in membranes (including neural porous membranes, Donnan equilibrium and steady-state transport) and transport through liquid membranes, particularly carrier-mediated transport.
(1.) Pletcher, D., A First Course in Electrode Processes, Alresford Press, UK, 1991.
It confirms realization of the same electrode processes as well as the similarity in electrochemical properties, for example, the charge transfer coefficients.
The enhancement is in part attributed to an exceptional increase in the local electromagnetic field (the "electromagnetic mechanism") and to an increase in the molecular polarizability (the "chemical" or "charge transfer mechanism").[3,4] This enhancement is exploited in the study of electrode processes. The power to see a fraction of a monolayer adsorbed on an electrode, while under potential and environmental control, in situ, has given the electrochemist a new set of eyes.