Chemistry Reference
In-Depth Information
Figure 3.4. Picture of running EC cells: (a) detail showing the crystals at the anode
(
) and (b) general view of the installation. (c) Single crystal of (BEDT-TTF)
2
I
3
grown by EC. Courtesy of Dr P. Batail.
+
of the electrolysis solvent is limited by its ability to dissolve both the organic donor
and the electrolyte. For this purpose, a mixture of two or more solvents may be
required. It becomes evident that the salt of the electrooxidized species must not
be soluble in those solvents.
The use of a stable and constant direct current source, the so-called galvanostatic
mode, allows control of the local concentration of electroactive species and thus
the rate of crystal growth. The other parameters involved (concentration, solvent
and temperature) essentially control the solubility of the crystalline phase. The ap-
propriate combination of these factors, together with the use of high-purity starting
materials, ultimately determines the success of the EC experiment. A picture of
a typical U-shaped EC cell is given in Figs. 3.4(a) and (b). Platinum wires, typi-
cally with diameters of 1 mm, are used as electrodes and both compartments are
separated by a fine porosity glass frit.
EC allows high-purity materials to be reproducibly obtained only if all materials
and chemicals involved are properly purified. This includes the glassware, which
should be thoroughly cleaned. Solvents of high-purity grade should be dried on
activated alumina or distilled just prior to use. Finally, the electrolyte, as well as the
