Effect of Co-doped graphene quantum dots to polyaniline ratio on performance of supercapacitor

Sulfur and nitrogen co-doped graphene quantum dots (S,N:GQDs) were prepared by a hydrothermal method. A series of polyaniline/S,N:G QDs nanocomposites (PGQDx where x is the mass of S,N:GQDs and equal to 0, 10, 20, 30, and 40 mg) has been synthesized via chemical in situ polymerization process. The UV-vis and Fourier transform infrared (FTIR) spectra showed an extra-doping level in H2SO4-doped polyaniline (PANI) due to -COOH groups of GQDs. However, increasing of GQDs content enhanced the aggregation of GQDs and reduced the doping level. The surface morphologies of nanocomposites showed a mixed of nanofibers, granules, and flakes with highly porous structure and particle size varied from 50 to 70 nm. Electrochemical properties of PGQD nanocomposites cast onto nickel-foam substrate as a supercapacitor electrode were performed in 2 M KOH electrolyte using cyclic voltammetry, charge/discharge, and electrochemical impedance techniques. PGQD20 exhibited maximum specific capacitance of 2524 F/g at 2 A/g with an excellent cyclic stability of 100% after 1000 cycle at scan rate of 50 mV/s. GQDs with unique properties reduces the charge transfer resistances, and promotes the contact between polyaniline and electrolyte and the electrochemical performance.