https://doi.org/10.1351/goldbook.E02238
The common value \(I_{0}\) of the anodic and cathodic partial currents when the reaction is at equilibrium \[I_{0}=I_{\text{a}}=- I_{\text{c}}\] For an electrode at equilibrium at which only one reaction is significant \(I=0\). When more than one reaction is significant at a given electrode, subscripts to \(I_{0}\) may be used to distinguish exchange currents. \(I\) is not usually zero when only one of these reactions is at equilibrium.