electrochemistry Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an outco ...

, there are two types of ideal electrode, the ideal polarizable electrode and the ideal non-polarizable electrode. Simply put, the ideal polarizable electrode is characterized by charge separation at the electrode-electrolyte boundary and is electrically equivalent to a capacitor, while the ideal non-polarizable electrode is characterized by no charge separation and is electrically equivalent to a short.

Ideal polarizable electrode

An ideal polarizable electrode (also ideally polarizable electrode or ideally polarized electrode or IPE) is a hypothetical

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...

characterized by an absence of net DC

current Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (stre ...

between the two sides of the

electrical double layer A double layer (DL, also called an electrical double layer, EDL) is a structure that appears on the surface of an object when it is exposed to a fluid. The object might be a solid particle, a gas bubble, a liquid droplet, or a porous body. The D ...

, i.e., no faradic current exists between the electrode surface and the electrolyte. Any transient current that may be flowing is considered non-faradaic.Vladimir Sergeevich Bagot'skiĭ, "Fundamentals Of Electrochemistry",John Wiley & Sons, 2006, p. 178. The reason for this behavior is that the electrode reaction is infinitely slow, with zero

exchange current density In electrochemistry, exchange current density is a parameter used in the Tafel equation, Butler–Volmer equation and other electrochemical kinetics expressions. The Tafel equation describes the dependence of current for an electrolytic process to ...

, and behaves electrically as a capacitor. The concept of the ideal polarizability has been first introduced by F.O. Koenig in 1934.

Ideal non-polarizable electrode

An ideal non-polarizable electrode, is a hypothetical electrode in which a faradic current can freely pass (without polarization). Its potential does not change from its equilibrium potential upon application of current. The reason for this behavior is that the electrode reaction is infinitely fast, having an infinite

, and behaves as an electrical short.

Real examples of nearly ideal electrodes

The classical examples of the two nearly ideal types of electrodes, polarizable and non-polarizable, are the mercury droplet electrode in contact with an oxygen-free KCl solution and the silver/silver chloride electrode, respectively.

References

Electrochemistry Electrodes {{electrochem-stub