Quantum Capacitance of Aryldiazonium Modified Large Area Few-Layer Graphene Electrodes

The quantum capacitance from large area, 6- to 7-layered graphene, and chemically modified graphene, was determined using electrochemical impedance spectroscopy measured at 100 Hz in a three-electrode electrochemical cell and aqueous acidic solution. Aryldiazonium chemistry was used to modify one side of the few-layered graphene sheets with methoxy- and iodo-phenyl groups. The graphene sheets were then mounted via an aqueous transfer method onto an epoxy substrate. It was found that both sides of the graphene sheets could be accessed by the electrolyte and thus the sheets were in a pseudo free-floating arrangement. The results show a complex quantum capacitance behavior with applied electrode potential, and that behavior was not stable with potential cycling. Chemically modified samples have similar quantum capacitance minimum to unmodified graphene, and all samples have a shallow U-shaped relationship with respect to applied electrode potential. The results show chemically modifying one side of few-layer graphene sheets using diazonium chemistry was not detrimental to the measured quantum capacitance minimum at the potential of zero charge, but the capacitance remained low over a large potential window which is not desirable for supercapacitor applications.