Carbon dot-infused gel polymer electrolytes: A new horizon for redox-enhanced supercapacitors

A new redox-based supercapacitor has been developed using carbon dots (CDs) derived from graphitic carbon nitride (gCN) and a biodegradable gel polymer electrolyte (GPE) composed of 2,3-hydroxyethyl cellulose (HEC) and polyvinyl alcohol (PVA) as the polymer base, glycerol (Gly) as a plasticizer, and sodium perchlorate (NaClO₄) as the doping salt, with activated carbon (AC) and graphene serving as electrodes. A unique combination of CDs with GPE increases the internal conductivity and stability of the matrix, which is discussed in this paper for the first time. Fourier transform infrared spectroscopy (FTIR) analysis identified key functional groups that support polymer[sbnd]CDs interactions. X-ray diffraction (XRD) revealed a semicrystalline nature with enhanced amorphous characteristics due to the addition of CDs and salt, promoting ionic conductivity. Thermal gravimetric analysis (TGA) showed thermal stability, with degradation steps at 30–200°C (moisture loss) and 200–470°C (polymer decomposition), which are suitable for energy storage applications. Scanning electron microscopy (SEM) images revealed a small globular cluster-like surface morphology. High-resolution transmission electron microscopy (HRTEM) images of the synthesized carbon dots revealed less than 10 nm sizes. The fabricated supercapacitor exhibited a maximum specific capacitance of 52 F/g for the AC electrode and 15 F/g for the graphene electrode, as determined via cyclic voltammetry (CV). Electrochemical impedance spectroscopy (EIS) analysis revealed that the AC electrode had less resistance than the graphene electrode. This means that the AC electrode had better ionic conductivity and electrode synergy. GCD analysis at a current density of 1 mA/g revealed that the graphene electrode achieved 11 F/g capacitance, 3.8 Wh/kg energy density, and 0.318 kW/kg power density. In contrast, the AC electrode exhibited 8 F/g, 2.8 Wh/kg, and 0.315 kW/kg, confirming redox contributions at the electrode/electrolyte interface.