Cobalt Oxide-Decorated on Carbon Derived from Onion Skin Biomass for Li-Ion Storage Application

Abstract

Onion waste, particularly onion skin, is a widely generated waste material, and harnessing its potential for energy storage aligns with sustainable development goals. Despite the high specific surface area exhibited by biocarbon derived from onion skin, its Li-ion storage performance is not desirable. In this study, biocarbon derived from purple onion skin serves as the substrate for accommodating cobalt oxide (Co3O4) through a hydrothermal method, employing Co(NO3)2·6H2O at various concentrations, and with and without prior activation using KOH treatment. The resulting samples undergo comprehensive analyses, including phase, morphological, surface, and electrochemical characterizations. The Co3O4 decoration on activated carbon derived from onion skin, synthesized using Co(NO3)2·6H2O at a concentration of 1 M, reveals a porous structure with a surface area of 702 m2/g, featuring predominant pore sizes of less than 5 nm. Significantly, the Li-ion storage performance of this sample surpasses that of alternative samples, demonstrating a remarkable reversible capacity of 451 mAh/g even after 500 cycles at an elevated current density of 2000 mAh/g. The charge transfer resistance of the sample (110.3 Ω) is found to be substantially lower than that of the sample prepared using carbonized onion skin biomass without activation. This research introduces an innovative approach leveraging onion skin waste as a template for Co3O4 decoration, thereby fabricating high-performance anodes for lithium-ion batteries.