The locus of the electrical centres of specifically adsorbed ions.
See also: outer Helmholtz plane
PAC, 1986, 58, 437. 'Interphases in systems of conducting phases (Recommendations 1985)' on page 448 (https://doi.org/10.1351/pac198658030437)
PAC, 1991, 63, 895. 'Nomenclature, symbols, definitions and measurements for electrified interfaces in aqueous dispersions of solids (Recommendations 1991)' on page 899 (https://doi.org/10.1351/pac199163060895)