Unlocking high energy density and stable electric double layer capacitor derived from sustainable biodegradable polymer electrolyte based on chitosan:polyvinyl alcohol: Potassium thiocyanate:xGlycerol (10≤x≤30)

• Development of Sustainable polymer electrolyte with enhanced energy storage properties. • Dielectric constant is higher than dielectric loss. • High energy density (11.26 W/kg) and power density (3176 Wh/kg) were achieved. • The EDLC device delivered high specific capacitance (≈80 F/g) and it has low ESR (30–40 Ohm) value. polyvinyl alcohol (PVA):potassium thiocyanate (KSCN) electrolytes utilizing casting methodology for electric double-layer capacitor (EDLC) energy conversion application. The Fourier Transform Infrared (FTIR) results established good interaction among the components of the plasticized electrolyte. The impedance study revealed that increasing the glycerol (GL) concentration resulted in a decrease in charge transfer resistance for K + ion movement. The dielectric constant is higher than that of the associated dielectric loss. A shift of the loss tangent peaks to higher frequencies was observed with increasing GL concentration. Additionally, a high ionic transference number (t ion = 0.952), derived from transference number measurement (TNM) measurements, confirms the dominant contribution of ions over electrons. The absence of current density up to an applied potential of 2.85 V indicates the electrochemical stability of the film below this threshold, demonstrating its suitability for energy storage applications. The nearly rectangular shape of the cyclic voltammetry (CV) curves at low scan rates indicates charge accumulation at the electrode–electrolyte interface, characteristic of non-Faradaic behavior. The galvanostatic charge–discharge (GCD) profiles exhibit a near-ideal triangular shape with minimal voltage drop, further supporting capacitive behavior. A stable specific capacitance of approximately 80 F/g, as obtained from GCD measurements, along with a high energy density of 11.26 Wh/kg, highlights the effectiveness of the biopolymer-based system for EDLC applications. Additionally, the device demonstrates excellent performance, achieving a high-power density of 3176 W/kg and exhibiting strong energy efficiency.