Title: Ilkovič equation Long Title: IUPAC Gold Book - Ilkovič equation DOI: 10.1351/goldbook.09139 Status: current Definition Equation relating electric current at a dropping mercury electrode under purely diffusional control, $I_{{\rm{d,}}t}$, the amount concentration of an electroactive substance at the drop surface $c$, and the concentration in bulk solution $c_{\rm{0}}$, \[I_{{\rm{d}},t} = -k\,z\,F\,D^{1/2}q_{\rm{m}}^{2/3} t^{1/6}(c - c_{0})\] where $k$ is a numerical constant, $z$ the electron number of an electrochemical reaction, $F$ the Faraday constant, $D$ the diffusion coefficient of the electroactive substance, $q_{\rm{m}}$ the mass flux of mercury at the dropping electrode, and $t$ the time elapsed from the beginning of the drop. Notes 1) At sufficiently large overpotentials, the surface concentration $c$ will fall to zero, giving a limiting diffusion current. \[I_{\rm{d,lim}} = k\,z\,F\,D^{1/2} q_{\rm{m}}^{2/3} t^{1/6} c_{0}\] Mostly, the average current (averaged over drop time and thus drop size) is calculated, when $t$ becomes the drop time $t_{\rm{d}}$. 2) The value of $k$ depends on the units used for quantities in the equation ($D$, $q_{\rm{m}}$, $t$, $c$), and whether the limiting current or the current averaged over the life of a drop is calculated. For $D$ in $\pu{cm2 s-1}$, $q_{\rm{m}}$ in $\pu{g s-1}$, $t$ in $s$, and $c$ in $\pu{mol cm-3}$, the constant $k$ is 708 (limiting current in $\pu{A}$) and 607 (average current in $\pu{A}$). Related Terms - dropping mercury electrode: https://goldbook.iupac.org/terms/view/09103 - electron number of an electrochemical reaction: https://goldbook.iupac.org/terms/view/09063 - mass flux: https://goldbook.iupac.org/terms/view/09144 Source - PAC, 2020, 92, 641. 'Terminology of Electrochemical Methods of Analysis (IUPAC Recommendations 2019)' on page 674 (https://doi.org/10.1515/pac-2018-0109) Other Outputs - html: https://goldbook.iupac.org/terms/view/09139/html - json: https://goldbook.iupac.org/terms/view/09139/json - xml: https://goldbook.iupac.org/terms/view/09139/xml Citation: Citation: 'Ilkovič equation' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.09139 License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. Collection: If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using. Accessed: 2026-06-28T07:55:56+00:00