3.4. Electrochemistry

Electrochemical measurements were performed on a BASiEpsilonE2P electrochemical analyzer (USA). The program handles wave Epsilon-EC-USB-V200. A conventional three-electrode system was used with glassy carbon for solutions or a carbon paste electrode (CPE) for powder samples as the working electrode, the Ag/AgCl (0.01 M) electrode as the reference electrode, and a Pt wire as the counter electrode. Then, 0.1 M Et₄NBF₄ was used as the supporting electrolyte for the determination of current−voltage characteristics. Acetonitrile was distilled over P₂O₅ and KMnO4 and then over molecular sieves. After purification, the solvent was stored under dry argon. Used as a base salt, Et₄NBF₄ was recrystallized from ethanol and dried in a vacuum chamber at 100 °C for 2 days. To study powder samples, a modified CPE working electrode was used. Its preparation was as follows: the carbon particles/phosphonium salt (dodecyl(tri-tert-butyl)phosphonium tetrafluoroborate) composite electrode was prepared by grinding a mixture of graphite powder and phosphonium salt in a ratio of 90/10 (w/w) in a mortar to give the homogeneous mass. A modified electrode was made in a similar manner, except that a part (ca. 5%) of graphite powder was replaced by samples under investigation. A portion of the resulting paste was packed firmly into the cavity (3 mm in diameter) of a Teflon holder.