Electrochemical characteristics of Co3O4 nanoparticles synthesized via the hydrothermal approach for supercapacitor applications

Cobalt oxide (Co3O4), a transition metal oxide known for its favourable capacitive properties and surface characteristics, is a promising candidate for electrode materials in supercapacitive energy storage applications. This study presents a comprehensive analysis of cobalt oxide nanoparticles synthesized through the hydrothermal method at varying synthesis temperatures, focusing on their structural, optical, electrochemical, and surface properties. X-ray diffraction analysis confirmed the cubic spinel structure of Co3O4, while Raman spectroscopy verified the phase composition of the nanoparticles. X-ray photoelectron spectroscopy offered insights into the near-surface chemistry of the synthesized material. The study determined two direct bandgaps of Co3O4 through absorption spectra and Tauc plots. To assess surface morphology and particle size distribution, field-emitting scanning electron microscopy and transmission electron microscopy were employed. Electrochemical investigations involved cyclic voltammetry and Nyquist plots, while galvanostatic charge-discharge tests demonstrated a specific capacitance (C-sp) of 450 Fg(-1) at 1 Ag-1. Impedance analysis indicated favourable capacitive behaviour with low charge transfer resistance. Furthermore, the study observed cyclic stability with a capacitive retention rate exceeding 88% at a current density of 20 Ag-1 over 10,000 cycles. The paper also discusses the capacitive and diffusion-controlled charge storage mechanisms at lower scan rates, emphasizing the potential of Co3O4 nanoparticles as the electrode material in the development of supercapacitor devices.