Ionic Liquids for the Future Electrochemical Applications

Abstract

Room temperature ionic liquids (RTILs) are the salts with weak interactions between the ions, which allows them to be liquid at room temperature (typically below 100°C). The scientific and technological importance of RTILs nowadays have spanned a wide range of applications, owing to their unique physicochemical properties, such as thermal and chemical stability, low melting point, negligible volatility, flame retardancy, high ionic conductivity, moderate viscosity, high polarity, and solubility (affinity) with many compounds (Fischer et al.; 1999; Welton, 1999; Earle & Seddon, 2000; Wasserscheid & Keim, 2000; Wasserscheid & Welton, 2003). For instance, RTILs are good solvents for a wide range of organic and inorganic compounds, which makes them an attractive solvent alternative for environmentally friendly processes. To date, there have been many reviews dealing with these topics. In particular, the easy modification of the cation and anion in RTILs is an advantage for the development of task-specific RTILs for organic synthesis, extraction, dissolution, etc. (Blanchard et al.,1999; Earle et al.,1999; Kubo et al., 2002). Electrochemical processes have been another important application area for RTILs since their early development. Key advantages of RTILs over common aqueous or organic media in this field are their wide electrochemical window (up to 6 V in some cases), high conductivity, and vanishingly low vapor pressure. These features not only facilitate investigations into metal electrodeposition (Hamelin et al., 1987; Schmickler, 1996; Freyland et al., 2003; Mann et al., 2009), electrocapacitor, and electrocatalysis in a less demanding manner, but also open up new possibilities for increased reactivity of processes and/or stability of reactants/products in ionic liquids (Hamelin et al., 1987; Dom & Mar, 2008). The subject of this chapter covers the newest aspects of ionic liquids in applications where their ion conductivity is exploited. Our goal in this chapter is to survey the recent key developments and issues within ionic liquid research in these areas. First, the current state of the knowledge of the ionic liquid/electrode interfaces, which is vital for applications and whose studies are still in its infancy, has been reviewed. As the range of available surface techniques and systematic, investigations increase, our understanding will improve which lead to advances on this field. Then, updated researches on the electrochemical applications of ionic liquids are exploited. In particular, their potentials as electrochemical solvents for metal/semiconductor electrodeposition, batteries and fuel cells are reviewed where conventional medias fail. Finally, the applications of ionic liquids in electrosynthesis, electrocatalysis, and electrochemical biosensing are briefly discussed. We conclude this