Insight into iodine-doped carbon xerogel electrodes on the capacitance and long-term stability of quasi-solid-state supercapacitors

• Carbon xerogel was synthesized via a cost-effective and straightforward method. • Self-supported electrodes were produced for supercapacitor applications. • Potassium iodide (KI) as a redox additive electrolyte was used. • Sulfonated poly (ether-ether-ketone) was adopted as electrolyte membrane. • Low self-discharge rate with a wide voltage range of 1.6 V was achieved. Current efforts to enhance the electrochemical performance of supercapacitors are primarily driven by advancements in nanostructured electrode materials, particularly through the optimization of electrical double-layer capacitance and pseudo-capacitance mechanisms. In this context, we demonstrate the feasibility of developing a supercapacitor employing carbon xerogel (CX)-based electrodes, a sulfonated poly(ether-ether-ketone) (SPEEK) membrane, and a potassium iodide (KI) redox additive in a sodium sulfate (Na 2 SO 4 ) electrolyte . The Na + -form SPEEK membrane acting as an ion conductor and electronic insulator, while the incorporation of potassium iodide (KI) at positive electrode significantly enhances the device’s electrochemical metrics, achieving a high specific capacitance of 200 F·g −1 , an energy density of 18.5 Wh·kg − 1 and low self-discharge rates. Electrochemical impedance spectroscopy further revealed outstanding stability, low resistance, and high capacitance retention over 20,000 charge–discharge cycles and additional 300 h of voltage-hold testing within a wide voltage window from 0 to 1.6 V. These findings highlight the strong potential of the developed quasi-solid-state supercapacitors as promising candidates for next-generation energy storage devices.