Differential capacitance (per unit area of interphase or electrode; SI unit F m-2) is given by \[C=(\frac{\partial Q}{\partial E})_{T,p,\mu _{i},...}\] where E is the potential of the electrode with respect to a reference electrode, µ i is a set of chemical potentials which are held constant, T is the thermodynamic temperature, Q is the electric charge (per unit area of interphase or electrode), and p is the pressure.