A cathodic current is the flow of electrical charge (usually carried by electrons) out of a working electrode into a second phase (usually an electrolyte solution) leading to the reduction of one or more species in the second phase.
As an example, consider a platinum working electrode immersed in an acidic solution of iron(III) chloride. If the platinum working electrode is poised at a sufficiently negative potential, any iron(III) cations in the vicinity of the electrode surface will gain an electron and be reduced to iron(II) cations according to the following half reaction:
In this case, the flow of electrons out of the working electrode as a result of the reduction of the iron(III) cations is a cathodic current.
Antonyms: anodic current