High Energy Density Heteroatom (O, N and S) Enriched Activated Carbon for Rational Design of Symmetric Supercapacitors

Carbon‐based symmetric supercapacitors (SCs) are known for their high power density and long cyclability, making them an ideal candidate for power sources in new‐generation electronic devices. To boost their electrochemical performances, deriving activated carbon doped with heteroatoms such as N, O, and S are highly desirable for increasing the specific capacitance. In this regard, activated carbon (AC) self‐doped with heteroatoms is directly derived from bio‐waste (lima‐bean shell) using different KOH activation processes. The heteroatom‐enriched AC synthesized using a pretreated carbon‐to‐KOH ratio of 1:2 (ONS@AC‐2) shows excellent surface morphology with a large surface area of 1508 m2 g−1. As an SC electrode material, the presence of heteroatoms (N and S) reduces the interfacial charge‐transfer resistance and increases the ion‐accessible surface area, which inherently provides additional pseudocapacitance. The ONS@AC‐2 electrode attains a maximum specific capacitance (Csp) of 342 F g−1 at a specific current of 1 Ag−1 in 1 m NaClO4 electrolyte at the wide potential window of 1.8 V. Moreover, as symmetric SCs the ONS@AC‐2 electrode delivers a maximum specific capacitance (Csc) of 191 F g−1 with a maximum specific energy of 21.48 Wh kg−1 and high specific power of 14 000 W kg−1 and excellent retention of its initial capacitance (98 %) even after 10000 charge/discharge cycles. In addition, a flexible supercapacitor fabricated utilizing ONS@AC‐2 electrodes and a LiCl/polyvinyl alcohol (PVA)‐based polymer electrolyte shows a maximum Csc of 119 F g−1 with considerable specific energy and power. Spine‐gelling performances: This study highlights the synthesis of novel activated carbon self‐doped with heteroatoms from lima‐bean shells, a biowaste. The activated carbon is used as electrodes in a symmetric supercapacitor utilizing 1 m NaClO4 and LiCl/polyvinyl alcohol as gel polymer electrolyte. The symmetric device shows a high specific capacitance of 191 F g−1 at 1 A g−1. Moreover, the device displays maximum specific energy and power of 21.48 Wh kg−1 and 14 000 W kg−1 with excellent capacitance retention of 98 % even after 10 000 cycles.