391908 Ionic Conductivities of Ionic Liquids and Solutions Containing Ionic Liquids
Ionic Conductivities of Ionic Liquids and Solutions Containing Ionic Liquids
Chaojun Shi, Liyuan Sun, Samuel Seo and Joan F. Brennecke*
Department of Chemical and Biomolecular Engineering
University of Notre Dame
Notre Dame, IN 46556
Ionic liquids have been considered for numerous electrochemical applications, ranging from electrolytes in lithium ion batteries and supercapacitors to media for electroplating. Their extremely low volatility presents the possibility of safer devices and lower environmental impact than aqueous acid and organic-based electrolyte solutions. Unfortunately, most ionic liquids have ionic conductivities that are too low for practical applications. Using a series of imidazolium and phosphonium ionic liquids with aprotic heterocyclic anions, we explore the key features that determine ionic conductivity. Conductivity, viscosity, density and ion diffusivity (from pulse gradient spin echo NMR spectroscopy) measurements indicate that both bulk viscosity and the association between the anion and the cation (as determined from Walden plots) determine the conductivity. We show how the cation-anion association that influences conductivity also influences the availability of the anion for reaction (with CO2).