Functionalized graphene sheets (FGSs) were tested as catalytic counter electrodes in dye-sensitized solar cells (DSSCs), showing performance comparable to platinum. FGSs, synthesized via thermal exfoliation of graphite oxide, have a large surface area and contain oxygen-containing functional groups. They were found to have catalytic activity for the reduction of triiodide, with charge-transfer resistance lower than platinum, though their overall efficiency was slightly lower. A new electrochemical impedance spectroscopy (EIS) equivalent circuit was proposed to interpret impedance spectra for porous carbon electrodes, which showed that FGSs have a higher charge-transfer resistance than platinum. Cyclic voltammetry (CV) measurements indicated that platinum has greater catalytic activity than FGSs, as measured by peak-to-peak separation (Epp). The catalytic activity of FGSs was found to be influenced by the C/O ratio, with higher ratios leading to increased apparent catalytic activity. The morphology of FGS electrodes was also found to affect apparent catalytic activity, with more porous electrodes showing better performance. FGS-based inks were demonstrated as flexible, conductive counter electrodes, showing efficiencies within 10% of platinum-based cells. The study concluded that FGSs could be used as cost-effective, flexible, and conductive counter electrodes for DSSCs, with further research needed to optimize their performance.Functionalized graphene sheets (FGSs) were tested as catalytic counter electrodes in dye-sensitized solar cells (DSSCs), showing performance comparable to platinum. FGSs, synthesized via thermal exfoliation of graphite oxide, have a large surface area and contain oxygen-containing functional groups. They were found to have catalytic activity for the reduction of triiodide, with charge-transfer resistance lower than platinum, though their overall efficiency was slightly lower. A new electrochemical impedance spectroscopy (EIS) equivalent circuit was proposed to interpret impedance spectra for porous carbon electrodes, which showed that FGSs have a higher charge-transfer resistance than platinum. Cyclic voltammetry (CV) measurements indicated that platinum has greater catalytic activity than FGSs, as measured by peak-to-peak separation (Epp). The catalytic activity of FGSs was found to be influenced by the C/O ratio, with higher ratios leading to increased apparent catalytic activity. The morphology of FGS electrodes was also found to affect apparent catalytic activity, with more porous electrodes showing better performance. FGS-based inks were demonstrated as flexible, conductive counter electrodes, showing efficiencies within 10% of platinum-based cells. The study concluded that FGSs could be used as cost-effective, flexible, and conductive counter electrodes for DSSCs, with further research needed to optimize their performance.