Biopolymer-based gel electrolyte integrated with ionic liquid and carbon quantum dots for high-performance sustainable supercapacitors

The demand for sustainable energy storage systems has intensified interest in gel polymer electrolytes (GPEs) that are biodegradable, efficient, and thermally stable. In this study, a novel GPE was developed using a xanthan gum (XG)/polyvinyl alcohol (PVA) blend embedded with carbon quantum dots (CQDs), magnesium chloride (MgCl 2 ), and the ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][NTf 2 ]). This work introduces a novel gel polymer electrolyte system, wherein the combined incorporation of an ionic liquid, MgCl 2 salt, and carbon quantum dots into a biopolymer matrix synergistically enhances ionic conductivity, thermal stability and electrochemical performance. The CQDs were synthesized hydrothermally via xanthan gum and characterized via photoluminescence (PL) spectroscopy, dynamic light scattering (DLS) and transmission electron microscopy (TEM), which were employed to evaluate the optical properties, size distribution, and morphology of the synthesized carbon quantum dots, respectively. The structural, thermal, and morphological properties of the GPE films were evaluated via Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Electrochemical impedance spectroscopy revealed enhanced ionic conductivity in the optimized GPE (P5), which was attributed to synergistic interactions between the IL, salt and CQDs, with a maximum conductivity of 4.0 mS/cm at 60 °C. The supercapacitor device fabricated via this GPE (AC ∣ P5 ∣ AC) demonstrated superior performance, delivering a specific capacitance of 124 F/g, an energy density of 11.1 W h/kg, and a power density of 266.6 W/kg from galvanostatic charge‒discharge measurements. Additionally, it retained 88.8 % of its capacitance after 1000 cycles, outperforming its IL-free counterpart. Overall, the integration of ionic liquids into biodegradable GPEs presents a viable pathway towards environmentally sustainable and high-performing supercapacitor systems. • Biodegradable GPEs developed using xanthan gum, PVA, CQDs, MgCl 2 , and ionic liquids. • Monodispersed carbon dots (∼11 nm) synthesized from xanthan gum. • The optimized GPE achieved 4.0 mS/cm conductivity and enhanced stability. • The supercapacitor had a capacitance of 124 F/g and 88.8 % retention after 1000 cycles. • Sustainable electrolyte system proposed for advanced energy storage applications.