Graphitic carbon nitride supported metal-free heterostructure embedded with carbon quantum dots and PEDOT as electrodes for supercapacitors

Energy storage technologies enable the efficient storage and release of energy, providing essential flexibility and stability to power grids worldwide. Supercapacitors are advanced energy storage systems capable of rapidly storing and releasing large amounts of electrical energy, offering long cycle life and high-power density. Herein, a carbon quantum dot (CQD) dispersed 2D graphitic carbon nitride (g-C₃N₄) nanocomposite was deposited with poly(3,4-ethylene dioxythiophene) (PEDOT) by an electrodeposition technique. The structural, morphological, functional group, and elemental characteristics of the synthesized materials were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). An electrochemical study of electrode materials named g-C₃N₄, g-C₃N₄-CQD and g-C₃N₄-CQD/PEDOT (GCP) composites was performed. The GCP electrode-based symmetric supercapacitor device exhibited a specific capacitance (C_s) of 109.5 F g⁻¹ at a current density of 0.2 A g⁻¹ in 1 M H₂SO₄. Herein, the prime novelty is the incorporation of CQDs as spacers between g-C₃N₄ layers, which substantially improved the surface area, providing potential benefits such as higher energy density and greater stability for supercapacitors. The supercapacitor device utilizing GCP demonstrated an energy density of 14.6 Wh kg⁻¹ at a power density of 1.4 kW kg⁻¹, operating at a current density of 0.2 A g⁻¹. The improved electrochemical performance of the hybrid electrode materials is ascribed to the combined effect of the faradaic PEDOT and the non-faradaic CQDs incorporated into the g-C₃N₄ matrix.