Electrical Double Layers Close to Ionic Liquid-Solvent Demixing

Electrical double layers (EDLs) play a key role in energy storage and have been suggested to have applications in energy generation. Recently, there has been an expansion of interest in EDLs, but EDLs with ionic liquid-solvent mixtures (ILSMs) received less attention. Herein, we study the temperature dependence of EDLs with ILSMs, in particular, close to demixing. We demonstrate the emergence of a bird-shaped capacitance, in addition to the well-known camel and bell shapes, which manifests the fine interplay between the electrostatic and wetting properties of ILSMs. We find that the capacitance increases appreciably as the system approaches demixing and this increase is accompanied by a sizeable enhancement of the energy storage, which can be utilized for generating electricity from waste heat.