The growing demands for environmental
and energy sustainability
drive the development of energy storage devices with high energy and
power densities and, consequently, potential electrode materials.
The conversion of biomass waste into sustainable electrode materials
has attracted much attention in the scientific community for energy
storage applications. In this work, porous carbon is derived from
the agricultural biowaste of the coconut tree (Cocos
nucifera) husk. This biowaste is activated through
a chemical activation method using different activating agents, such
as K2CO3, KOH, KMnO4, KCl, KBr, and
KI. Among the samples, biomass-derived carbon activated using the
KMnO4 activating agent (AC3) delivers a high specific surface
area of 2333.4 m2 g–1 with a pore volume
of 2.625 cm3 g–1, which results in excellent
electrochemical performance, with a gravimetric capacitance of 560
F g–1 at 2 A g–1 current density
in 2 M KOH electrolyte solution. To demonstrate the real-time application,
symmetric aqueous (KOH) and gel [poly(vinyl alcohol)-PVA/KOH] electrolyte
devices are fabricated using the AC3@graphite sheet as positive and
negative electrodes. The fabricated symmetric gel electrolyte device
achieves a high gravimetric capacitance of 276 F g–1 at the current density of 2 A g–1. The above device
manifests an energy density of 38.3 Wh kg–1 at a
power density of 1 kW kg–1. Besides, the cycle stability
retains 98% even after 5000 cycles at 10 A g–1 current
density. These superior electrochemical outcomes suggest that this
AC3@graphite sheet electrode will have potential in electric double-layer
supercapacitors.