## Wikipedia - Sovratensione (elettrochimica) (it) concentration overpotential

https://doi.org/10.1351/goldbook.C01230
The concentration @[email protected] of an @[email protected] at a given @[email protected] ($$\text{c.d.}$$) is basically the difference in equilibrium potentials across the @[email protected] More precisely, it is the potential of a @[email protected] (of the same @[email protected] as the @[email protected] ) with the interfacial concentrations which establish themselves at $$\text{c.d.}$$, relative to the potential of a similar @[email protected] with the concentrations of the bulk solution. From such a measured potential difference, with $$\text{c.d.}$$ flowing, one needs to subtract the ohmic potential drop prevailing between the two electrodes.
Source:
PAC, 1981, 53, 1827. (Nomenclature for transport phenomena in electrolytic systems) on page 1838 [Terms] [Paper]