Room temperature ionic liquid reference

Room Temperature Ionic Liquid Reference Electrodes... 

Ionic liquids are also sometimes referred to as molten salts, nonaqueous ionic liquids (NAILs) or room temperature ionic liquids, and all of these names are entirely valid. The term molten salt is now used less frequently, and generally... 

The term ionic liquid (IL) refers to a class of liquids that are composed solely of ions. It is a synonym of molten salt. Although molten salt imphcitly means a high-temperature hquid that is prepared by melting a crystalline salt, IL includes a new class of ionic compounds that are liquids at the ambient temperature [1]. Thus, IL in a narrow sense often stands for room-temperature ionic liquid (RIL). In the present chapter, IL is used in a broader sense and, if necessary, RIL is used to clarify that it is liquid at the ambient temperature. The history of ILs has aheady been reviewed [2]. 

Ionic liquids (ILs) are basically salts with poorly coordinated ions, resulting in low melting points. Since low is a relative term (NaCl, for example, is an IL between 801 °C and 1465 °C), chemists use it to refer either to salts which melt below 100 °C, or to salts that are liquid at 25 °C. The latter group is known as room-temperature ionic liquids (RTILs). In most RTILs, one of the ions is organic, with a delocalized charge. Note that ILs are not concentrated salt solutions. They are nonmolecular liquids which contain, in theory, no water (in practice, many ILs contain at least traces of water). 

This discussion of the structure and dynamics of fused salts provides only the briefest overview of their properties. However, even this minimal background will prove a useful reference point as we turn our attention to room temperature ionic liquids. 

Reference Electrodes for Use in Room-temperature Ionic Liquids... 

Voltammetric, electrodeposition, electrosynthetic and electroanalytical studies are carried out in room-temperature ionic liquids (RTILs) by a significant and increasing number of both industrial and academic laboratories [23-25], Such studies, when carried out at anything other than a very empirical level, require the use of a reference electrode . The purpose of this chapter is to address the special problems this poses and their solutions. First, however, we start by considering the essential features of a reference electrode in general. 

Ionic liquids once referred almost exclusively to molten salts, i.e., salts with melting points well above room temperature, although eutectic mixtures of salts can dramatically reduce melting points. Nowadays, there is a range of ionic compounds that are liquid at room temperature, and often much lower temperatures. Room temperature ionic liquids with properties that are conducive towards synthetic chemistry are described in Section 1.26.3. 

The tenns ionic liquid and room temperature ionic liquid will be used interchangeably from this point, unless otherwise stated, where the former would ordinarily refer to an ionic hquid that is in a liquid state under ambient conditions and the latter to an ionic liquid that has a melting point lower than 373.15 K. 

Silvester DS, Ward KR, Aldous L, Hardacre C, Compton RG (2008a) The electrochemical oxidation of hydrogen at activated platinum electrodes in room temperature ionic liquids as solvents. J Electroanal Chem 618 53-60 Silvester DS, Rogers El, Compton RG, McKenzie KJ, Ryder KS, Endres F, MacFarlane D, Abbott AP (2008b) Reference electrodes for use in room-temperature ionic liquids. In Endres F, MacFarlane DR, Abbot A (eds) Electrodeposition from ionic liquids. Wiley, Weinheim, pp 296-309... 

There will be considerable activity in the optimisation of ion transport parameters within the non-classical electrolyte systems discussed in this section. Future prospects for research in this area are likely to involve combination of aspects of the systans referred to above (e.g. the use of room-temperature ionic liquids in conjunction with ionomers) to achieve improvements in performance of energy storage systems. 

Figure 12.3 SEM images of electrospun cellulose fiber in room temperature ionic liquid with organic co-solvents. RTIL/DMF (a) 1 0.5, (b) 1 0.75, (c) 1 1, RlL/DMAc (d) 1 0.5, (e)l 0.75, (f) 1 1. (Adapted from Reference [97]).

Occasionally also the use of so-caUed pseudo reference electrodes has been reported (see Chap. 14). Such pseudo reference electrodes became popular in polarography but especially in cyclic voltammetry, employing three electrode arrangements. They consist of a silver or platinum wire or activated carlxMi dipping into the electrolyte. They substitute for a reference electrode. Such electrodes were reported to exhibit very stable potentials. The ease of such an arrangement was also used in electrochemical studies in (room temperature) ionic liquids. It must be pointed out that electrode potentials versus such electrodes are meaningless as such arrangements do not constitute thermodynamic values. 

In this book, there are other chapters related to nonaqueous systems. Chapter 1 by Inzelt is on the electrode potentials and includes a section on the problem to relate the electrode potentials between different media. Chapter 2 by Gritzner is on the reference redox systems in nonaqueous systems and their relation to water. Chapter 3 by Tsirlina is on the liquid junction potential and somewhat deals with the problem between different solvents. Chapter 7 by Bhatt and Snook is on the reference electrodes for room temperature ionic liquids. See these chapters as well. 

Experimental techniques for handling high temperature molten salts have been developed for many more years than those for room temperature ionic liquids. Considerable experimental challenges need to be overcome to find a stable reference electrode that will survive high temperatures (often up to 1,000 °C) and highly corrosive molten salt environments. 

Snook GA, Bond AM (2010) Reference electrodes for electrochemical studies in room temperature ionic liquids. In Torriero AAJ, Shidthky MIA (eds) Electrochemical properties and applications of ionic liquids. Nova, New York... 

The term ionic liquid (IL) refers to a class of liquids that are composed solely of ionsi. It is a synonym for molten salt. IL in a narrow sense often indicates room-temperature ionic liquid (RIL) that exists as a liquid at room temperature. 

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