Electrical Double Layers In Neat and Hybrid Ionic Liquids Electrolytes

Room-temperature ionic liquids (RTILs) are an emerging class of electrolytes that are composed exclusively of organic cations and organic/inorganic anions. RTILs  have attracted significant attention in fundamental and applied research in recent years. The extensive interest is in part due to their wide electrochemical windows, excellent thermal stability, and non-volatility, which make them exceptionally useful in diverse electrochemical devices.  However, the relatively low ionic conductivity of typical RTILs hinders their widespread applications. To address this issue, hybrid electrolytes, i.e., mixture of organic solvents and RTILs, have been developed recently. Interestingly, some of the key properties of RTILs, e.g., low inflammability and wide electrochemical window, are not compromised.

In this work, we study the electrical double layers (EDLs) in neat and hybrid ionic liquid electrolytes. We examine the specific capacitance and molecular structure of the EDLs, and how they change as the mass fraction of organic solvent changes. Some unexpected results, e.g., insensitive dependence of the EDL capacitance on the organic solvent mass fraction, were obtained. We will rationalize these observations using a simple analytical model for the EDLs.