Commercial graphene nanoplatelets in the form of optically transparent thin films on F-doped SnO2 (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 methoxyproplonitrile solution (Z946). Optical spectra and electrochemical impedance confirm that the film's absorbance scales linearly with R-CT(-1). Electrocatalytic properties of grephene 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. 03 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.