Ionic Liquid--Electrode Interface: from One Law To Fit Them All to One Model To Predict Them All

The electric double layer (EDL) -- arguably the central concept in electrochemistry -- remains the nut everyone wants to crack, as its properties control the performance of electrochemical devices. One such property is the differential capacitance, a quantity that determines energy density in supercapacitors. In this letter, we show that for ionic liquid--electrode interfaces, where steric packing results naturally in a power-law scaling, the capacitance--potential dependence can be fitted with a four-parameter model. We demonstrate, first, how these parameters can be evaluated and used to interpret EDL structure and properties; and second, how the model enables predictions of both differential capacitance and energy density.