Ionic room-temperature electrochemical

Table 3.6-2 The room-temperature electrochemical potential windows for binary and ternary chloroaluminate and related ionic liquids.

The early history of ionic liquid research was dominated by their application as electrochemical solvents. One of the first recognized uses of ionic liquids was as a solvent system for the room-temperature electrodeposition of aluminium [1]. In addition, much of the initial development of ionic liquids was focused on their use as electrolytes for battery and capacitor applications. Electrochemical studies in the ionic liquids have until recently been dominated by work in the room-temperature haloaluminate molten salts. This work has been extensively reviewed [2-9]. Development of non-haloaluminate ionic liquids over the past ten years has resulted in an explosion of research in these systems. However, recent reviews have provided only a cursory look at the application of these new ionic liquids as electrochemical solvents [10, 11]. 

Recently, room temperature ionic liquids (RT-ILs) have attracted much attention for their excellent properties, e.g., wide temperature range of liquid phase, ultra-low vapor pressure, chemical stability, potential as green solvents, and high heat capacities [64,65]. These properties make them good candidates for the use in many fields, such as thermal storage [66], electrochemical applications, homogeneous catalysis [67], dye sensitized solar cells [68], and lubricants [69,70]. 

Recently, a eutectic mixture of choline chloride and urea (commercially known as Reline) was used as a medium from which CdS, as well as CdSe and ZnS, thin films were electrodeposited for the first time [53]. Reline is a conductive room-temperature ionic liquid (RTIL) with a wide electrochemical window. The voltammetric behavior of the Reline-Cd(II)-sulfur system was investigated, while CdS thin films were deposited at constant potential and characterized by photocurrent and electrolyte electroabsorbance spectroscopies. 

We have also demonstrated that well-behaved quantized charging of gold MPCs is possible in air- and water-stable room-temperature ionic liquids, such as 1-hexyl-3-methylimidazolium tris(penta-fluoroethyl)-trifluorophosphate (HMImEEP), Fig. 30c, d [334, 335]. As ionic liquids have very attractive features, including nearzero vapor pressure, considerable thermal stability, and an electrochemical stability window that often exceeds 4 V, this demonstration is particularly significant from a technological point of view. 

Ionic liquids, having per definition a melting point below 100 °C, and especially room temperature ionic liquids (RTIL) have attracted much interest in recent years as novel solvents for reactions and electrochemical processes [164], Some of these liquids are considered to be green solvents [165]. The scope of ionic liquids based on various combinations of cations and anions has dramatically increased, and continuously new salts [166-168] and solvent mixtures [169] are discovered. The most commonly used liquids are based on imidazolium cations like l-butyl-3-methylimidazolium [bmim] with an appropriate counter anion like hexafluorophos-phate [PFg]. Salts with the latter anion are moisture stable and are sometimes called third generation ionic liquids. 

Voltammetry at a glassy carbon (GC) electrode was used to study of the electrochemical deposition of CdTe from the Lewis basic l-ethyl-3-methylimidazolium chloride/tetrafluoroborate room temperature ionic liquid [208]. 

The utility of ionic liquids can primarily be traced to the pioneering work by Osteryoung et al. [3] on N-butylpyridinium-containing, and by Wilkes and Hussey [4—6] on l-ethyl-3-methylimidazoHum-containing ionic Hquids for electrochemical studies. These studies have strongly influenced the choice of ionic Hquids for subsequent research [7]. The vast majority of work pubHshed to date on room-temperature ionic Hquids relates to N-butylpyridinium and l-ethyl-3-methyHmidazoHum [EMIM] tetrachloroaluminate(III) systems. The large variety of available ion combi-... 

Lu, X., Zhang, Q., Zhang, L., and Li, J., Direct electron transfer of horseradish peroxidase and its biosensor based on chitosan and room temperature ionic liquid, Electrochem. Commun., 8,874-878,2006. 

Ding, S.F., Xu, M.Q., Zhao, G.C., and Wei, X.W., Direct electrochemical response of Myoglobin using a room temperature ionic liquid, l-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate, as supporting electrolyte, Electrochem. Commun., 9, 216-220,2007. 

Wang, S.F., Chen, T., Zhang, Z.L., and Pang, D.W., Activity and stability of Horseradish Peroxidase in hydrophilic room temperature ionic liquid and its application in non-aqueous biosensing, Electrochem. Commun., 9, 1337-1342, 2007. 

Hewlett, P. C., Brack, N., Hollenkamp, A. E, Forsyth, M., and MacFarlane, D. R., Characterization of the lithium surface in N-methyl-N-alkylpyrrolidinium bis(trifluoromethanesulfonyl)imide room-temperature ionic liquid electrolytes, /. Electrochem. Soc., 153, A595-A606,2006. 

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