High performance quasi-solid-state supercapacitor based on activated carbon derived from asparagus waste

Supercapacitors with carbon electrodes derived from biomass and utilizing gel polymer electrolytes are currently a focal point in the development of highly efficient, environmentally friendly, and cost-effective energy storage devices. In this study, we present porous activated carbon derived from asparagus waste, prepared through chemical activation with ZnCl 2 followed by physical activation with CO 2 , as a high-performance electrode material for supercapacitors. The performance of electrodes has been discussed in comparison with supercapacitors employing both gel polymer electrolytes and conventional liquid electrolytes i.e. 7 M KOH. The flexible film of the gel polymer electrolyte exhibits noteworthy characteristics, including a high ionic conductivity of ∼6.3 mS cm −1 , and a high electrochemical stability window of ∼4.5 V. Supercapacitors prepared with this gel polymer electrolyte outperform supercapacitors with liquid electrolytes thanks to a broader electrochemical stability window, showing optimal charge-discharge performance, a specific capacitance of 160 F g −1 , a specific energy of 31 Wh kg −1 , and an effective power of 0.56 kW kg −1 . The superior rate performance is demonstrated by powering a LED for a substantial duration, highlighting the exceptional capabilities of the system. Additionally, the supercapacitor employing the gel polymer electrolyte displays an extended stability, sustaining approximately 10,000 charge-discharge cycles with only a modest initial fading of ∼16 % in specific capacitance and maintaining a high coulombic efficiency of ∼100 %. • Supercapacitors derived from asparagus waste and with ionic liquid-based gel polymer electrolytes have been developed. • Optimized activation of biomass waste has been obtained by combining chemical and physical processes. • Up to 4.5 V stability window of gel polymer electrolytes allowed to reach 31 Wh kg −1 specific energy.