Annealing-mediated tuning of sol-gel synthesized CoFe₂O₄ nanoparticles for supercapacitor

In this study, cobalt ferrite nanoparticles (CFO NPs) were synthesized by sol-gel method and annealed at different temperatures (350°C, 650°C, and 800°C) for supercapacitor application. X-ray diffraction analysis revealed the formation of cubic spinel-structured CFO NPs. With increasing annealing temperature, the crystallite size and crystallinity of CFO NPs increased, while the dislocation density and microstrain decreased. The potential use of these CFO NPs as an electrode for supercapacitors was investigated using cyclic voltammetry (CV), electrochemical impedance spectroscopy, and galvanostatic charge–discharge tests. The CV curves of the CFO NP–modified electrode showed a typical pseudocapacitive behavior. The CFO NPs annealed at 350°C (CFO-350) exhibited the highest specific capacitance of 855 F/g at 1 A/g due to their smaller crystallite size, higher surface area, and higher defect density. Furthermore, CFO-350 electrode displayed an energy density of 10.23 Wh/kg at a power density of 898.24 W/kg. In conclusion, the electrochemical performance of the CFO NPs can be tuned by controlling their crystallite size, defects, and surface properties through annealing at different temperatures.