Nonmetallic solid electrodes

In the case of metallic electrodes, any change in the electrode potential, E, always occurs at the interfacial potential, A4>H> between the metal and the solution. The amount of change in the electrode potential, then, is equal to that in the interfacial potential, which arises across what we call the Helmholtz layer or the electrical compact double layer. This is, however, not the case for nonmetallic solid electrodes such as ionic or covalent semiconductors, at which the interfacial potential usually remains constant irrespective of the electrode potential. 

In the older battery literature the term separator is frequently used very loosely, to include all nonmetallic solid components between the electrodes, such as supporting structures for active materials (tubes, gauntlets, glass mats), spacers, and separators in a narrow sense. In this section, only the last of these, the indispensable separating components in secondary cells, will be termed separators , distinguished from the others by their microscopically small pores, i.e., with a mean diameter significantly below 0.1 mm. 

When the electrode material is nonmetallic, and an inert metal must be used to act as an electrical conductor, the convention is to write the i mbol of the inert metal, e.g.. Ft, to the left when an oxidation electrode is implied and to the right when a reduction process is to be inferred. The order of writing the components of the solution is immaterial, although if one is a gas or a sparingly soluble liquid or solid it is usually written next to the inert metal. The following are oxidation electrodes ... 

Electrolyte - A nonmetallic (liquid or solid) conductor that carries current by the movement of ions (instead of electrons) with the liberation of matter at the electrodes of an electrochemical cell. 

Electrocrystallization of a nonmetallic phase can be a secondary effect, arising when saturation of the electrolyte by the product of the electrode reaction is reached. It can, however, also result from direct formation of the product by a solid state reaction. 

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