(476c) A Comparative Study of Room Temperature Ionic Liquids and Their Organic Solvent Mixtures Near Charged Electrodes | AIChE

(476c) A Comparative Study of Room Temperature Ionic Liquids and Their Organic Solvent Mixtures Near Charged Electrodes


Vatamanu, J. - Presenter, University of Utah
Bedrov, D. - Presenter, University of Utah
Borodin, O. - Presenter, Army Research Lab

Due to increasing demand for portable and nonpolluting energy, the theoretical and experimental research of electrical energy storage devices, such as electrochemical batteries and electric double layer supercapacitors, has increased significantly in the last decade. Understanding the structure of electrode-electrolyte interfaces is key to understand the mechanisms of the energy storage in supercapacitors. Furthermore, the distribution of species near charged surfaces can reveal possible pathways and initial stages of Faradic processes. In this context extensive theoretical and modeling research is dedicated to understanding the electric double layer (EDL) structure. In this presentation we will comparatively discuss the properties of C2mim-BF4, C8mim-BF4 and NEt4-BF4 room temperature ionic liquids (RTILs) and their solutions with acrylonitrile (ACN) solvent. We will first show the role of electrode material, electrode geometry, applied temperature, electrolyte composition and applied electrode potential on the structure of EDL and the corresponding differential capacitances (DC). We found that within the interfacial layer the close solvation shells of ions can be dramatically different from those found in bulk electrolyte and are very sensitive to the applied electrode potential. Due to its large dipole moment, the ACN solvent competes with the dissolved ions to adsorb on the surface generating a non-Gouy-Chapman behavior for the EDL and DC dependence on potential.  The negative electrodes generate smaller DCs than the positive ones for all investigated electrolytes. This is effect is likely due to a weaker surface polarization by the bulkier cations and it is more pronounced for cations with larger alkyl tail. Finally, the insertion of NEt4-BF4 dissolved in ACN in nanoporous electrodes of slit geometry has been also studied. In contrast with previous results for neat RTIL electrolytes and in agreement with several recent experiments we found only a modest increase of capacitance in subnanometer pores.