# What does “electrochemically active species” mean in the expression for the mass-transfer limited current?

The expression for the mass-transfer limited current $i$ is given by $i = nFAmC$.

where $C~[\mathrm{mol\, cm^{-3}}$] represents the concentration of the electrochemically active species that gets converted at the electrode; if the entire analyte gets converted, then $C$ is equal to the initial bulk concentration of the analyte.

I am confused as to what electrochemically active species mean? Is that just saying the ions in solution? Or is it the oxidized ion and the reduced ion?

• it is the concentration of the reactants. So in $\ce{O + e- -> R}$ which is a reduction, it is the concentration of O, which is the oxidized species. – Burak Ulgut Jan 18 '17 at 13:49