Electrochemical terminology

Figure 1.1. Basic electrochemical terminology as introduced by Faraday in ref. 1. Reprinted with permission from the Royal Society.

The interfaces between a semiconductor and another semiconductor (e.g. the very important pin junction, the interface between p- and ft-type semiconductors), between a semiconductor and a metal (the Schottky barrier) and between a semiconductor and an electrolyte are the subject of solid-state physics, using a nomenclature different from electrochemical terminology. 

The work of Davy was continued and expanded upon by the great English scientist Michael Faraday (1791-1867). Faraday s primary studies in electrochemistry took place between 1833 and 1836. Faraday is responsible for giving us much of our modern electrochemical terminology. The terms electrode, anode, cathode, electrolyte, anion, cation, and electrolysis are all attributed to Faraday. Even more important than his qualitative description of electrochemistry, Faraday did quantitative studies that led to his formulation of electrochemical laws. These laws provided a means to determine the relationship between current and the amount of materials reacting in an electrochemical reaction. Because Faraday s major contributions are still used today, they are covered in the principles of electrochemistry later in the chapter rather than in this historical section. 

We now look at some examples of redox reactions involving simple cations in aqueous solution. Electrochemical terminology will often be encountered, since e.m.f. measurements on electrochemical cells are important sources of thermodynamic data in this area. For example, the reduction potential ° for the half-reaction ... 

Thus, in terms of partial current densities, let the reaction be proceeding in the forward direction under equilibrium conditions and let its velocity be represented by j. The arrow represents direction. If you like, you can say, From left to right. Now we choose to use electrochemical terminology, and then the full definition of j would be the partial current density in one direction. (The density refers to the standardization with respect to the area one is considering, a square centimeter [cm2] or square meter [m2].) If we were talking about a chemical reaction, then we should use the symbol v and the definition then would be the rate of reaction in one direction. In a chemical reaction, v would be the number of gram moles per square centimeter per second (g mol cm-2 s-1) (or per square meter per second [m-2 s-1]). 

The above nomenclature can, without any difhculty, be made compatible with the electrochemical terminology. The hygroscopic water corresponds to the IHL the solvation water to the term OHL, and the captive water to the term diffuse layer. In addition, the colloid structure provides for an interface between the OHL and the diffuse layer, called outer Helmholtz plane (OHP), the precondition for any and all electrochemical reactions. The electrical potential between the OHL and the diffuse layer is known as zeta potential, or electrokinetic potential. 

In electrochemical terminology, the vessel in which electrochemical transformation occurs is called the cell. To bring the terminology in line with that of chemical reaction engineering, we refer to it as the electrochemical reactor (ECR). An ECR is one in which electrical energy is converted into chemical... 

As in any heterogeneous reaction, two major controlling regimes are also possible in electrochemical reactions, surface reaction and external mass transfer, referred to specifically as surface overpotential (or charge transfer) and concentration overpotential, respectively, in electrochemical terminology. 

Consider the simple electrode reaction 21.3. Usually, any such primary reaction is accompanied by a side reaction that leads to a reduction of current efficiency. Such a reaction is referred to as a loss reaction in electrochemical terminology. The major loss reaction is the hydrogen evolution reaction... 

The pipe is cedled the "working electrode in electrochemical terminology. 

The generic mechanism above is denoted in electrochemical terminology as an E(C )J mechanism, that is, an initial electrochemical step (the radical cation generation), followed by polymer propagation via successive chemical (combination with monomer radical cation, proton loss) and electrochemical (oxidation to generate oligomeric radical cations) steps, and likely termination via a chemical step. The... 

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