Effect of Activation Environment on Coconut-Husk-Derived Porous Activated Carbon for Renewable Energy Storage Applications

Abstract

As a major agro waste of coconut, coconut husk is presented here as a cheap, abundant, novel, and sustainable green source of high-surface-area activated carbon for high-performance supercapacitor electrodes. The present communication satisfies one of the United Nations Sustainable Development Goals (UN goals) as an affordable, reliable, and sustainable solution for the existing energy technologies. The carbonization and the activation via a one-step integrated microwave pyrolysis system and vacuum furnace, respectively, are the production technologies used for the conversion of biomass into activated carbon. The chemical impregnation was performed in two different agents (KOH and H 3 PO 4 ) and three higher activation temperatures (700, 800, and 900 °C), and their physical properties and the supercapacitive performances were analyzed and compared. A high surface area of 1218 m 2 g −1 was achieved for KOH impregnation (AC KOH 900) with a weight ratio of AC to KOH of 1:2 at an activation temperature of 900 °C, yielding an excellent specific capacitance of 342 F g −1 , much higher than that of activated carbon with H 3 PO 4 activation (243 F g −1 ). The energy storage performance was further carried out by fabricating a symmetric supercapacitor device in aqueous and polymer gel (PVA-H 3 PO 4 ) electrolyte media, and excellent cyclic stability of nearly 100% was achieved with high power density for both KOH-and H 3 PO 4 -activated samples at high temperature, which can be interconnected with its enhanced surface area and high porosity that facilitates fast ion transport and improves energy storage performance. The fabricated supercapacitor cells, when used to power two red LEDs, showed a complete discharge at the end of 15 min while a maximum glow for 30 min was achieved for a single LED, which took 1 h for its complete discharge. Furthermore, via the present investigation, coconut-husk-derived activated carbon shows promise as a high capacitance, low cost, and renewable material, consequently suggesting a promising avenue toward high-power, affordable, renewable, and clean energy storage devices.