Effect of double hydrothermal synthesis technique on the electrochemical properties of Co₃O₄ microflowers for supercapacitor application

This study presents a systematic approach for synthesizing spinel-structured Co₃O₄ thin films using a double hydrothermal synthesis method, followed by an annealing treatment. Variations in reaction time and the incorporation of additional cobalt ions (Co²⁺) during a secondary hydrothermal process affect the morphology of the synthesized Co₃O₄ film and its corresponding physicochemical properties. It results in distinctive ultrathin flower-like structures composed of uniformly grown nanowires with diameters ranging from 17 to 84 nm on a conductive substrate. Through this synthesis strategy, we found that C₄ thin film with longer reaction times exhibits superior average specific capacitance, reaching 1072.67 F g^-1 at a scan rate of 10 mV s^-1, with an effective mass loading of 8.2 mg cm^-2. The synthesis process assists a substantial amount of active material present on the substrate and creates a unique morphology that increases the surface area available for electrode–electrolyte interaction. This increased surface area facilitates more efficient charge transfer and storage, thereby enhancing the electrochemical performance of the thin film. Consequently, this approach offers a promising pathway for developing high-performance materials for energy storage applications.