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ELECTROCHEMISTRY

Their good electric conductivity [1] in wide electrochemical windows [2-4] are probably the major reasons why electrochemical applications are one of the biggest areas of ionic liquid research. In fact the early days of ionic liquids research (in the mid 20 th century) were dominated by their application as electrochemical solvents when a research project was started at the US Air Force to find a replacement for the LiCl/KCl molten salt electrolyte used in thermal batteries.

Only until recently most of the research concentrated on the use of haloaluminate ionic liquids. However with the development of water stable and commercially available non haloaluminate ionic liquids over the past ten years an explosion on publications has occurred on these systems.

Besides their properties mentioned above, their ability to solvate a wide range of inorganic, organic and organometallic materials and their wide liquidus range make ionic liquids attractive as solvents for the investigation of electrochemical processes. From the physico-chemical data the trend in the electrochemical stability of cations is pyridinium < pyrazolium < imidazolium < sulfonium < ammonium. The anion stability towards oxidation is halides < chloroaluminates < fluorinated anions < triflate anions. Besides the electrochemical window the conductivity of ionic liquids have been measured with values between 1 and 20 mS/cm. It is important to stress that the behaviour of ionic liquids as electrolytes is strongly influenced by their transport properties. In order to evaluate them, ion-diffusion-coefficients and ion-transport numbers have been measured by electrochemical or by NMR methods.

Current applications of ionic liquids in the electrochemical area include (but are not limited to) their use in lithium-ion batteries, supercapacitors and their use of solvents for the electrodeposition of metals and semiconductors. To give another example, ionic liquids have been used in polymer electrolyte systems [5] where they play the role of both a charge carrier and a non-volatile plasticizer.

It can be expected that in the near future new anion classes with even superior electrochemical properties than the present systems will be available.

Solvent Innovation offers an electrochemistry kit with specially selected ionic liquids.

For more information about conductivities of specific ionic liquids or to learn more about ionic liquids in electrochemical applications please contact markus.wagner@solvent-innovation.com

[1] P.C. Trulove, R.A. Mantz, "Ionic Liquids in Synthesis", P. Wasserscheid, T. Welton (Eds.), Wiley-VCH, Weinheim, 2003 .

[2] de Souza et al., New. J. Chem. , 2000 , 24 , 1009.

[3] H. Matsumoto, M. Yanagida, K. Tanimoto, M. Nomura, Chem. Lett. 2000 , 922.

[4] R. A. Osteryoung et al., J. Electrochem Soc., 1997 , 144 , 3881.

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