# Faradaic current

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{{short description|Electric current generated by a redox reaction at an electrode}}

In [electrochemistry](/source/electrochemistry), the '''faradaic current''' is the [electric current](/source/electric_current) generated by the reduction or oxidation of some [chemical substance](/source/chemical_substance) at an [electrode](/source/electrode) (i.e. by the [redox reaction](/source/Redox) between a substance and an electrode).<ref name="SkoogHoller2017">{{cite book|author1=Douglas A. Skoog|author2=F. James Holler|author3=Stanley R. Crouch|title=Principles of Instrumental Analysis|url=https://books.google.com/books?id=D13EDQAAQBAJ&pg=PA576|date=27 January 2017|publisher=Cengage Learning|isbn=978-1-337-46803-9|pages=576–}}</ref><ref name="Cazes2004">{{cite book|author=Jack Cazes|title=Analytical Instrumentation Handbook, Third Edition|url=https://books.google.com/books?id=DN2zCrS6wywC&pg=PA534|date=30 November 2004|publisher=CRC Press|isbn=978-0-8493-9039-5|pages=534–}}</ref> The net faradaic current is the [algebraic sum](/source/Summation) of all the faradaic currents flowing through an [indicator electrode](/source/indicator_electrode) or [working electrode](/source/working_electrode).<ref>{{GoldBookRef | file = F02321 | title = faradaic current}}</ref>

==Limiting current==
The '''limiting current''' in electrochemistry is the limiting value of a faradaic current, which is approached as the rate of charge transfer to an [electrode](/source/electrode) is increased. It can be approached by increasing the [electric potential](/source/electric_potential) of the electrode or decreasing the rate of [mass transfer](/source/mass_transfer) to the electrode. It is independent of the applied potential over a finite range, and is usually evaluated by subtracting the appropriate residual current from the measured total current. A limiting current can have the character of an [adsorption](/source/adsorption), [catalytic](/source/catalytic), [diffusion](/source/diffusion), or kinetic current, and may include a migration current.

==Migration current==
The migration current is the difference—for any particular value of the indicator or working electrode potential and any ionic electroactive substance—between:

* the current that would be obtained if there were no transport of the substance due to the electric field between the electrodes, and
* the current that is actually obtained for the reduction or oxidation of the substance.

Following the [sign convention](/source/sign_convention) for current, the migration current is negative for the reduction of a cation or for the oxidation of an anion, and positive for the oxidation of a cation or the reduction of an anion. Hence, the migration current may tend to either increase or decrease the total current observed.

The migration current approaches zero as the [transport number](/source/Ion_transport_number) of the electroactive substance is decreased. This is achieved by increasing the concentration of the [supporting electrolyte](/source/supporting_electrolyte), and hence the conductivity.

== See also ==
* [Butler–Volmer equation](/source/Butler%E2%80%93Volmer_equation)
* [Gas diffusion electrode](/source/Gas_diffusion_electrode)

==References==
{{reflist}}

Category:Electrochemistry

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