Hydrothermal synthesis of self-supported hierarchical microflowers of Co3O4 nanowires for potential supercapacitor application

This study explores the synthesis of ultrathin flower architecture of spinel-structured Co₃O₄ electrodes, on nickel foam using a double hydrothermal method, followed by annealing at 250 °C for 4 h. We systematically investigate the effects of varying reaction times and additional Co²⁺ treatment during the second hydrothermal process on the morphology and electrochemical properties of Co₃O₄. Field emission scanning electron microscopy (FE-SEM) images confirm the formation of self-supported hierarchical flowers, characterized by sharp, spike-like nanowires (16–33 nm in diameter) arranged radially. The self-supported optimized hierarchical Co₃O₄ thin film, characterized by its unique architecture and substantial mass loading of 4.6 mg cm⁻², achieved an impressive specific capacitance of 749.48F g⁻¹ at a scan rate of 10 mV s⁻¹ (specific capacity of 182.16 mAh g⁻¹) in 2 M KOH electrolyte and retained 64 % of its initial capacitance after 5000 cycles. Furthermore, a symmetric device demonstrated the ability to illuminate a red LED for approximately 120 s when two devices were connected in series.