SYNTHESIS OF ORGANIC ELECTROACTIVE MATERIALS IN IONIC LIQUIDS - Electrochemical Nanofabrication: Principles and Applications - page 118

solar cells [18-20] and sensors [21-24]. Properties of ILs that
are crucial for the above-mentioned applications are high
ionic conductivity [5], high viscosity [5], low melting point
(below 100°C) [6, 7], sufficient thermal stability [3], and a wide
electrochemical window [8, 9]. Another advantage is that the
organic structure of the ions gives possibility to almost unlimited
combinations of anions and cations leading to various kinds of ILs
by manipulating the size of both anionic and cationic parts giving the
desired properties [25, 26]. The toxicity of ILs has been discussed
by Matzke et al. [27]. They found some toxicity in the studied ILs,
and therefore, the commonly accepted claim that ILs are nontoxic is
not necessary always valid. However, ILs still have one big advantage
over the conventional organic solvents: the almost negligible vapor
pressure [28]. Figure 3.1 presents some of the most common ions in
ILs used in electrochemistry.

Anions:

Cations:

O

O

F

R 1 R 2 N -

R 1

R 2

F F

F

F
F

S

N + P -

S

N +

N

F

F F

O O

F

F

F

Br - Cl -

Imidazolium Pyrrolidinium

Figure 3.1 Structure of ionic liquids.

The electrochemical window of electrolytes is very crucial
in electrochemical applications. ILs are electrochemically rather
stable having an electrochemical window typically from 2 to even
6 V. The electrochemical stability of the ILs depends on redox
reactions of both the anion and the cation. Anions such as Tf

N

-

2

oxidize at relatively high anodic potentials compared with, for
example, BF

-

resulting in extended stability of ILs containing Tf N

-

4 2

[6, 29]. Also, tetraalkylammonium cation-based ILs show extended
electrochemical window on the negative side of the
potential scale [30]. Another important issue connected with the
electrochemical properties of ILs is the influence of moisture. In
chloride-based ILs, the addition of water produces HCl, which is
then reduced further, greatly changing the electrochemical
response of IL [31]. Also, the residual water can drastically decrease
the electrochemical window. Shröder et al. studied the impact