Term: contact potential difference (Volta potential difference) https://doi.org/10.1351/goldbook.C01293 Definition: The electric potential difference between one point in the vacuum close to the surface of M1 and another point in the vacuum close to the surface of M2, where M1 and M2 are two uncharged metals brought into contact. Related Terms: 1) electric potential (http://doi.org/10.1351/goldbook.E01935). Source: PAC, 1983, 55, 1251. 'Interphases in systems of conducting phases (Provisional)' on page 1257 (https://doi.org/10.1351/pac198355081251) Citation: 'contact potential difference (Volta potential difference)' 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.C01293 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. 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.