Differential capacitance (per unit area of @[email protected] or electrode; SI unit \(\text{F m}^{-2}\)) 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 @[email protected], \(\mu _{i}\) is a set of @[email protected] which are held constant, \(T\) is the @[email protected], \(Q\) is the @[email protected] (per unit area of @[email protected] or electrode), and \(p\) is the pressure.