This occurs when the specifically adsorbed amount of charge in the
inner Helmholtz plane
is higher than the charge on the metal phase, taken with the reverse sign.
PAC, 1986, 58, 437
(Interphases in systems of conducting phases (Recommendations 1985))
on page 448
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook