concentration overpotential 

https://doi.org/10.1351/goldbook.C01230
The concentration overpotential of an electrode reaction at a given electrode current density (c.d.) is basically the difference in equilibrium potentials across the diffusion layer. More precisely, it is the potential of a reference electrode (of the same electrode reaction as the working electrode) with the interfacial concentrations which establish themselves at c.d., relative to the potential of a similar reference electrode with the concentrations of the bulk solution. From such a measured potential difference, with 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]
Citation: 'concentration overpotential' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.C01230 RIS BibTex EndNote
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Last revised: September 12, 2008