Dead Ashoka (Saraca asoca) leaves–derived porous activated carbons and flexible iongel polymer electrolyte for high-energy-density electric double-layer capacitors

In this work, porous activated carbons (ACs) are synthesized from dead Ashoka leaves by a modified chemical activation method where KOH and K₂CO₃ are used as activating agent in different weight percentages. The irregular surface morphology, high surface area, and the substantial amount of micropores and mesopores volumes simultaneously have been found in the synthesized ACs. The surface morphology and porosity parameters of ACs have been found significant with changing the incorporated activating agents in the different weight percentages. These porous ACs derived from biowaste material have been tested as electrode material in the electric double-layer capacitors (EDLCs) with iongel polymer electrolyte (iPE). A series of iPEs have been prepared using PVdF-HFP polymer host, 1-ethyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([PYR₁₂][TFSI]) ionic liquid, and mixed organic carbonate-based plasticizers. EDLCs have been fabricated using AC-based electrodes and flexible iPE30 solid electrolyte. The high ionic conductivity (~6.11 × 10^‑3 S.cm^‑1 at 303 K), good electrochemical stability window (~ ‑2.74 V to +3.14 V vs. stainless steel electrodes), and flexible nature of the freestanding film of iPE30 provided outstanding compatibility with bio-derived AC electrodes. Cyclic voltammetry and galvanostatic charge–discharge studies have been performed, which show ideal and reversible capacitive features together with good cyclability of the fabricated EDLC cells.