(533e) Understanding Electrochemical Double Layer Structure and Capacitance of Ionic Liquids/Graphene-like Electrode in Supercapacitors

There has been an increasing interest in investigations on room temperature ionic liquids (ILs) toward supercapacitor applications, because they are environmentally friendly, nonvolatile, and sustain high voltages without decomposition.  Despite its importance, a fundamental understanding of the arrangements of ions and capacitance at the interface between an IL and an electrode is still lacking.  In this work, we investigated the microstructure and capacitance of electric double layers (EDLs) at the interface between [BMIM][PF₆] and graphene-like electrodes using combined classical molecular dynamics and density functional theory calculations.  We find that the EDL capacitance of graphene-like electrodes in ionic liquids (ILs) can be significantly increased by the shape and surface topology of the electrode.  We will discuss the reason for this enhancement in terms of EDL packing, orientation, and cation-anion segregation.  We will also discuss the impact of the electrode modification on the total interfacial capacitance (C_T) by combining EDL capacitance and electrode quantum capacitance (C_Q), as C_T strongly depends on the contribution of both C_D and C_Q.  The improved understanding will provide a valuable insight towards strategies for the rational design of electrolyte and electrode materials to maximize interfacial capacitance in supercapacitors.