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.^[1]

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:^[2]

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 process^[3]), the net current density on the electrode is zero:^[2]

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:^[1]

${\displaystyle I=\Sigma I_{a,j}+\Sigma I_{c,j}}$

where the index ${\displaystyle j}$ refers to the particular reactions.

• Bard, A.J. and Faulkner L.R. Electrochemical Methods: Fundamentals and Applications (2nd ed.), 2001 John Wiley & Sons Inc.

• Exchange current density

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