Ajwa Date Seed-Derived Hydrogel Electrolyte with Enhanced Electrochemical Performance and Mechanical Strength for Flexible Supercapacitors

Background: The growing demand for sustainable, high-performance energy storage systems has intensified interest in biomass-derived materials for supercapacitor applications. This study presents a green and scalable approach to fabricating novel electrodes and solid-state electrolytes using Phoenix dactylifera (Ajwa date) seed biomass and palm waste-derived activated carbon. Methods: KOH-activated carbon from date pits was employed to enhance surface area and redox activity. A double-network hydrogel electrolyte (DSHC) was synthesized by incorporating 0.5 g of date seed powder with sodium alginate and wheat starch (0.2 g each), followed by chemical crosslinking in 2 M H2SO4. Structural and physicochemical properties were analyzed using SEM, XRD, and FTIR, while electrochemical performance was evaluated through cyclic voltammetry and galvanostatic charge–discharge measurements. Results: SEM revealed a densely ordered porous network with regular cylindrical channels favorable for ion transport. XRD and FTIR confirmed amorphous carbon formation and effective molecular crosslinking. The hydrogel electrolyte exhibited a wide potential window of ~2 V and strong pseudocapacitive behavior, delivering a maximum specific capacitance of 179 F g−1 at 5 mV s−1 and a discharge capacitance of 159 F g−1 at 0.2 A g−1, with excellent stability over 5500 cycles. Conclusions: Agricultural waste-derived materials demonstrate strong potential as low-cost, eco-friendly, and mechanically robust components for flexible supercapacitors, suitable for sustainable energy storage and rapid-charging applications.