Enhanced Physical Properties of Cobalt Oxide Nanoparticles for Energy Storage Applications

Cobalt dioxide (CoO₂) nanostructured material was synthesised via a solid-state reaction using cobalt nitrate tetrahydrate (Co(NO₃)₂·4H₂O) and sodium hydroxide (NaOH) as precursors. The resulting materials were fabricated into three distinct working electrodes and evaluated electrochemically in a three-electrode configuration using 3 M KOH as the electrolyte. Cyclic voltammetry revealed pronounced redox peaks, which confirmed Faradaic charge storage behaviour. At a scan rate of 10 mV·s⁻¹, the specific capacitances of CoO₂ samples annealed at 25 °C, 250 °C and 300 °C were 223, 348 and 473 F g⁻¹, respectively. This indicated improved performance with increasing annealing temperature. X-ray diffraction patterns showed characteristic peaks corresponding to the (111), (112), (200), (211) and (311) planes, which confirmed the crystalline nature of the CoO₂ nanostructures. Annealing was found to significantly influence morphology, crystallinity and electronic properties, with the bandgap narrowing from 2.00 eV (unannealed) to 1.77–‍1.86 eV (annealed). These results demonstrate that thermal treatment enhances the electrochemical and structural properties of CoO₂, which highlights its potential as a high-performance electrode material for next-generation energy storage devices.