Onion Husk-Derived High Surface Area Graphene-Like Carbon for Supercapacitor Electrode Material Application

Abstract

This article presents the synthesis of graphene-like carbon (GLC) from onion husk, which is used as a precursor for applications as electrode material in energy storage devices. GLC is considered a promising electrode material for supercapacitor due to its excellent microstructural and electrical properties. The synthesis of GLC from biowaste is of great importance due to its natural abundance and low cost. GLC was synthesized from onion husk (OH) through pre-carbonization at 550OC, followed by subsequent thermochemical activation using KOH at temperatures of 600OC, 850OC, and 950OC, aimed at determining the optimal activation parameters. The structure and morphology of the obtained GLC samples were studied by SEM, X-ray diffraction, BET, and Raman spectroscopy. The electrochemical characteristics of the obtained electrodes were carried out using an Elins P-40X electrochemical workstation. The surface morphology of the graphene-like carbon from onion husk (GLC-OH) samples, following carbonization at 550OC, exhibits distinct thermal stratification of the material. This stratification, upon activation in KOH, facilitates the development of high-porosity graphene-like carbon flakes. The XRD and Raman spectroscopy results reveal the emergence of few-layer graphene with a substantial number of structural defects at 850OC, while at 950OC, the formation shifts towards multilayer graphene. The synthesized GLC-OH powder was used as an active electrode material in the symmetric electrochemical capacitor. The electrochemical characterization of the assembled capacitor using GLC-OH at 850OC revealed a notably higher specific capacitance value of 131 F/g, along with a Coulomb efficiency of 98% at a gravimetric current density of 1 A/g. Also, at 850OC, it showed a high specific surface area (SSA), and it is 1924 m2 g-1 according to the Brunauer-Emmett-Teller method. This exceeds the values obtained for the other two samples at 600OC and 950OC. The obtained results illustrate the efficacy of utilizing graphene-like carbon derived from onion husk waste, demonstrating its potential as a promising material for high-capacity supercapacitors.

Keywords: onion husk, graphene-like carbon, carbonization, activation, electrode, capacity, supercapacitor.