Anion sensitive voltammetry of fullerene C 60 dissolved in 1,2-dichlorobenzene deposit in contact with aqueous electrolyte Wojciech Adamiak, Galyna Shul, Marcin Opallo * Institute of Physical Chemistry, Polish Academy of Sciences, ul. Kasprzaka 44/52, 01-224 Warszawa, Poland article info Article history: Received 9 September 2008 Received in revised form 21 October 2008 Accepted 24 October 2008 Available online 31 October 2008 Keywords: Fullerene 1,2-Dichlorobenzene Ion transfer Liquid/liquid interface Redox reaction abstract Electroreduction of C 60 dissolved in hydrophobic solvent deposited on the electrode surface was studied. A microliter amount of C 60 and tetrahexylammonium perchlorate solution in 1,2-dichlorobenzene was deposited on basal plane pyrolytic graphite electrode and this electrode was immersed into an aqueous solution. The voltammetry shows three consecutive reduction–oxidation steps. The redox potential of first electroreduction step is sensitive on anion but not on cation present in the aqueous phase. This parameter also depends on electrolyte concentration in the aqueous and organic phase. It is proposed that electroreduction of C 60 is preceded by anion exchange and followed by anion expulsion to the aque- ous phase. Similar anion effect on the redox potential is also observed for unsupported deposit indicating importance of initial partitioning of electrolyte into the organic phase. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction The redox properties of C 60 molecule [1,2] are fascinating, be- cause it can accept sequentially up to six electrons and these steps can be detected by voltammetry [3,4]. The reaction rate of first step of C 60 electroreduction is fast due to insignificant reorganisation energy of molecule and its relatively large size [5–7]. Electrochem- istry of fullerene films also involves many electron transfer steps and is electrolyte sensitive [8]. This is because of the cation inser- tion into film following electrochemical reduction step. Despite the fullerene insolubility in water little attention was paid to electro- chemical behavior of C 60 in system consisting of electrified li- quid/liquid interface [9,10]. This reaction site seems to be important due to recent numerous reports on liquid/liquid precip- itation of different forms of C 60 [11]. Also the electrochemical behavior of fullerene dissolved in the liquid deposit on the elec- trode surface [12,13] was not reported. Here, the voltammetry of C 60 dissolved in 1,2-dichlorobenzene (ODCB) deposit on the electrode surface is reported. This solvent was chosen because of relatively good fullerene solubility (>10 2 mol dm 3 ). We show that when such liquid modified elec- trode is immersed into aqueous solution three electroreduction steps can be seen. Moreover the redox potential corresponding to C 60 =C  60 redox couple depends on the anion present in the aqueous phase. 2. Experimental 2.1. Chemicals Fullerene C 60 (sublimed, 99.9%, Aldrich), tetrahexylammonium perchlorate (THxAP) (electrochemical grade, Fluka), 1,2-dichloro- benzene (ODCB) (Aldrich, anhydrous, 99%), KPF 6 (98 + %, Merck) and other inorganic salts of analytical grade from POCh: KClO 4 , KBr, KNO 3 , NH 4 ClO 4 , NaSCN, NaClO 4 and LiClO 4 were used as re- ceived. Water was filtered and demineralised with the ELIX system (Millipore). 2.2. Instrumentation Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were performed with the Autolab (Eco Chemie) electro- chemical system. The working electrode was a disc electrode (0.126 cm 2 ) of basal plane pyrolytic graphite (bppg) purchased from NT-MDT Ò . Platinum wire (diameter 0.5 mm) and an Ag/ AgCl/KCl sat. electrode were used as the counter and reference electrode, respectively. All electrodes were placed in the cap of the cell and immersed into the aqueous salt solution. 2.3. Procedures In order to obtain fresh bppg electrode surface prior to each experiment, Scotch tape was used. Typically 1 ll of 0.01 mol dm 3 fullerene and 0.1 mol dm 3 THxAP solution in ODCB was deposited on the electrode using micropipette. Then bppg electrode was 1388-2481/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2008.10.048 * Corresponding author. Tel.: +48 22 632 32 21; fax: +48 22 343 33 33. E-mail address: mopallo@ichf.edu.pl (M. Opallo). Electrochemistry Communications 11 (2009) 149–152 Contents lists available at ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom