Electrochemically formed two-component films comprised of fullerene and transition-metal components

This paper reviews the results of investigations into the electrochemical formation and properties of redox-active films formed from fullerenes and selected transition-metal complexes. These polymeric films are formed on the electrode surface during electroreduction of a solution containing a fullerene or a fullerene derivative and complexes of Pd(II), Pt(II), Rh(II) and Ir(l). The polymeric network is formed through covalent bonding between the transition-metal atoms (or complexes) and the fullerenes. Films containing C-60 exhibit electrochemical activity in the negative potential range due to the reduction of the fullerene component. In this potential range, a decrease in the film resistance is also observed. In the case of the well-studied C-60/Pt and C-60/Pd films, the polymer formation process may also be accompanied by deposition of metal nanocrystals if a high ratio of metal complex to fullerene is used during film formation. The presence of this metallic phase in the film influences its morphology, structure, and electrochemical properties. Films formed from C-60 with covalently bound electron-donating groups exhibit electrochemical activity in both negative and positive potential ranges. Since these systems exhibit both p- and n-doping properties, they can be called 'double cables'. These fullerene/transition-metal films may have considerable potential for a number of applications. They can be used as charge storage materials for batteries and photovoltaic devices. The C-60/Pd film can be also used as an electrochemical sensor. Films of C-60/Pd and C-60/Pt containing metallic palladium or platinum particles catalyze hydrogenation of olefins and acetylenes. Laser ablation of electrochemically formed C-60/M and C-70/M films (M = Pt or Ir) results in the fragmentation and formation of hetero-fullerenes such us [C59M](+) and [C58M](-).