Sulfur and nitrogen-doped graphene quantum dots/PANI nanocomposites for supercapacitors

Abstract

Sulfur and nitrogen-doped graphene quantum dots/polyaniline (S,N-GQDP) nanocomposites are prepared by a two-step synthesis method. The heteroatoms (sulfur and nitrogen) doped graphene quantum dots (S,N-GQDs) are first prepared by a hydrothermal method and then mixed with aniline at three different concentrations, followed by polymerization to form S,N-GQDP1, S,N-GQDP2 and S,N-GQDP3 nanocomposites. Various physicochemical characterization techniques are used to confirm the formation of S,N-GQDs and their interaction with polyaniline (PANI) in S,N-GQDP nanocomposites. Fourier transform infrared (FTIR) and Raman spectral analyses confirm the delocalization of electrons in the polymer backbone of S,N-GQDP through electrostatic interaction and the π–π interaction between S,N-GQDs and pristine PANI. The pristine PANI and the three-different nanocomposites are used as electroactive materials to assess the energy storage properties. The S,N-GQDP2 composite has pine cone shape-like particles with a high surface area (154 m² g⁻¹). The doping of heteroatoms improves the electrical conductivity and increases the reactive sites that act as trap sites for enhanced ion storage. The S,N-GQDP2 nanocomposite shows a highest specific capacitance of 645 F g⁻¹ at a current density of 0.5 A g⁻¹ in the three-electrode configuration. The S,N-GQDP2 composite-based symmetric cell shows an energy density of 17.25 Wh kg⁻¹ (corresponding device capacitance of 124.2 F g⁻¹ at a current density of 1 A g⁻¹) at a power density of 500 W kg⁻¹. A high volumetric energy density of 18.11 Wh L⁻¹ is obtained at a volumetric power density of 525 W L⁻¹. In addition, the S,N-GQDP2 nanocomposite-based symmetric device shows good cycling stability for 1000 cycles with a capacitance retention of 90%.