Composition, structure, surface topography, and electrochemical properties of electrophoretically deposited nanostructured fullerene films

Nanostructured fullerene films of controlled surface topography have been prepared by electrophoretic deposition from toluene-ethanol mixed solvent solutions. Atomic force microscopy (AFM) imaging of the films revealed that the size of the C-60 grains could be readily controlled by the time Of C-60 aggregation in bulk solution before deposition and by the strength of the dc electric field applied during the deposition. The deposition was monitored by piezoelectric microgravimetry with the use of an electrochemical quartz crystal microbalance. The mass of the C-60 film increased exponentially with the time of deposition. The corresponding decrease of the deposition rate with time was presumably due either to the growth of larger C-60 aggregates in solution of lower mobility or blocking effect of the electrode surface by insulating C-60 deposits. In the accessible potential window of 0.1 M (TBA)PF6, in acetonitrile, cyclic voltammetry (CV) curves for the C-60 films featured four cathodic peaks corresponding to four one-electron reductions. Simultaneously recorded multiscan curves of current, resonant frequency change, and dynamic resistance change versus potential for a potential range covering the first two electroreductions, in which the film was relatively stable with respect to dissolution, indicated pronounced transformations in the film caused by the solvent-assisted dynamic equilibria of ions of the supporting electrolyte. However, scanning the potential beyond the second reduction of the fullerene film resulted in a gradual mass decrease due to dissolution of the film. The charge-related piezoelectric microgravinietry, X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (XRD) analyses indicated reversible ingress of both TBA(+) counterion and PF6- co-ion into the C-60(-) film. The experimental control over three-dimensional surface assembling of fullerene clusters demonstrated in the present study opens up new avenues to design fullerene electrode materials of high surface area.