Migrational flux, electroactive ions

The equation must be written separately for each species in solution (the anion and cation of the electrolyte, the oxidized and reduced forms of the electroactive couple, and any ion accompanying the initial state of the electroactive substance). Note that the charge of each species (z) controls the direction of the migrational flux, and for a neutral molecule (z = 0), the term on the right disappears as expected. Simultaneous solution of the five equations and evaluation over the appropriate boundary conditions gives the current for conditions when migration of either (or both) members of the electroactive couple can occur. 

It is evident that the migration flux of the electroactive ions can be decreased or even eliminated by the addition of an excess of indifferent electrolyte since, in this case, ti 0, consequently 7m 0. This means that the limiting current in the case of the reduction of a cation (e.g., Cu " ) will decrease as the concentration of the inert electrolyte (e.g., KNO3) is increased. 

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