Commercial graphene nanoplatelets in the form of optically transparent thin films on F-doped SnO(2) (FTO) exhibited high electrocatalytic activity toward I(3)(-)/I(-) redox couple, particularly in electrolyte based on ionic liquid (Z952). The charge-transfer resistance, R(CT), was smaller by a factor of 5-6 in ionic liquid, compared to values in traditional electrolyte based on methoxypropionitrile solution (Z946). Optical spectra and electrochemical impedance confirm that the film's absorbance scales linearly with R(CT)(-1). Electrocatalytic properties of graphene nanoplatelets for the I(3)(-)/I(-) redox reaction are proportional to the concentration of active sites (edge defects and oxidic groups), independent of the electrolyte medium. Dye-sensitized solar cell (DSC) was assembled with this material as a cathode. Semitransparent (>85%) film of graphene nanoplatelets presented no barrier to drain photocurrents at 1 Sun illumination and potentials between 0 and ca. 0.3 V, but an order of magnitude decrease of R(CT) is still needed to improve the behavior of DSC near the open circuit potential and, consequently, the fill factor. We predict that the graphene composite is a strong candidate for replacing both Pt and FTO in cathodes for DSC.