https://doi.org/10.1351/goldbook.L03577

An equation which gives the electric charge per unit area of an interface (electrode): \[(\frac{\partial \gamma }{\partial E_{\text{A}}})_{T,p,\mu _{i}\neq \mu }=- Q_{\text{A}}\] where γ is the interfacial tension, EA is the potential of a cell in which the reference electrode has an interfacial equilibrium with one of the ionic components of A, Q A is the charge on unit area of the interface, µ i is the chemical potential of the combination of species i whose net charge is zero, T is the thermodynamic temperature and p is the external pressure. Since more than one type of reference electrode may be chosen, more than one quantity Q may be obtained. Consequently Q cannot be considered as equivalent to the physical charge on a particular region of the interphase. It is in fact an alternative way of expressing a surface excess or combination of surface excess of charged species.*Sources: *

PAC, 1974,*37*, 499. 'Electrochemical nomenclature' on page 508 (https://doi.org/10.1351/pac197437040499)

PAC, 1986,*58*, 437. 'Interphases in systems of conducting phases (Recommendations 1985)' on page 445 (https://doi.org/10.1351/pac198658030437)

PAC, 1974,

PAC, 1986,