Novel hierarchical porous carbon derived from biomass Citrus limetta pulp for high-performance quasi-solid-state supercapacitor electrodes

Herein, we introduce citrus limetta pulp-derived activated carbon (AC) electrodes in high-performance symmetric electrical double-layer capacitors (EDLCs). Dried leftover limetta pulp has been activated with varying amounts of activating agent (KHCO3) to yield a variety of activated carbons. NH4+-salt (ammonium trifluoromethanesulfonate, NH4Tf) and ionic liquid IL (1-ethyl-3-methylimidazolium-trifluoromethanesulfonate, EMITf) incorporated gel polymer electrolytes (GPEs) interfaced with AC from the pulp have been evaluated for EDLCs' performance. Structural properties of the synthesized activated carbons have been conferred by XRD and Raman spectroscopy, whereas the morphology and the porosity have been visualized and optimized through SEM and BET analyses. Optimum characteristics of EDLCs have been depicted by the presence of micro- and mesoporosity in ACs. Free-standing film of GPE NH4Tf/IL entrapped in poly(vinylidinefluoride-co-hexafluoropropylene) (PVdF-HFP) demonstrates excellent compatibility with AC-electrodes due to their high ionic conductivity at room temperature (2.4 × 10−3 S cm−1), good electrochemical stability window (3.6 V), and flexible nature. Results elucidate that the electrochemical properties of the gel polymer electrolyte were improved by the addition of NH4+-salt, which in turn affected the EDLCs' overall performance. By adding NH4+ the specific capacitance of the EDLC cell-2 improved from 156 F g−1 to 165 F g−1. Energy density and power density for this cell (with GPE containing NH4+-salt) have been measured to be 25.66 Wh kg−1 and 14.35 kWkg−1, respectively. Moreover, the specific capacitance of EDLC cell-2 is retained at 80 % up to 6200 charge-discharge cycles.