partial current

In electrochemistry, partial current is defined as the electric current associated with (anodic or cathodic) half of the electrode reaction.

Depending on the electrode half-reaction, one can distinguish two types of partial current:

• cathodic partial current I_c (called also cathodic current): is the flow of electrons from the electrode surface to a species in solution;
• anodic partial current I_a (called also anodic current): is the flow of electrons into the electrode from a species in solution.

The cathodic and anodic partial currents are defined by IUPAC.{{GoldBookRef |title=partial anodic (cathodic) current |file=P04407 }}

The partial current densities (i_c and i_a) are the ratios of partial currents respect to the electrode areas (A_c and A_a):

:i_c = I_c/A_c

:i_a = I_a/A_a

The sum of the cathodic partial current density i_c (positive) and the anodic partial current density i_a (negative) gives the net current density i:[http://electrochem.cwru.edu/ed/dict.htm Electrochemistry Dictionary and Encyclopedia] {{webarchive|url=http://webarchive.loc.gov/all/20011125103514/http%3A//electrochem.cwru.edu/ed/dict.htm |date=2001-11-25 }}

:i = i_c + i_a

In the case of the cathodic partial current density being equal to the anodic partial current density (for example, in a corrosion processB. Elsener, [http://www.surface.mat.ethz.ch/education/courses/surfaces_and_interfaces/chapter11 Corrosion and durability of metals] {{webarchive|url=https://web.archive.org/web/20120918210609/http://www.surface.mat.ethz.ch/education/courses/surfaces_and_interfaces/chapter11 |date=2012-09-18 }} , p. 252.), the net current density on the electrode is zero:

:i_eq = i_c,eq + i_a,eq = 0

When more than one reaction occur on an electrode simultaneously, then the total electrode current can be expressed as:

:$I\; =\; \backslash Sigma\; I\_\{a,j\}\; +\; \backslash Sigma\; I\_\{c,j\}$

where the index $j$ refers to the particular reactions.