Synthesis of the ZnCo₂O₄ Positive Electrode Using a Urea-Assisted Hydrothermal Approach for Supercapacitor Applications

Spinel-structured oxides are cost-effective and environmentally friendly, making them attractive candidates for supercapacitor electrode applications. However, their limited electrical conductivity and low energy density hinder their widespread utilization. In this study, ZnCo₂O₄ nanomaterials were synthesized using a simple hydrothermal method, followed by a calcination process with controlled urea molar concentration. The resulting samples exhibited a significant specific surface area, which reduced the widths of ion diffusion channels while simultaneously increasing the number of active sites. At a current density of 7 mA/cm², the ZnCo₂O₄ nanoparticles synthesized with a 0.9 M urea concentration demonstrated a remarkable specific capacitance of 635 F/g. Furthermore, the performance evaluation revealed an energy density of 31.9 W h/kg and a power density of 143.7 W/kg. In its assembled configuration, the asymmetric supercapacitor exhibited an energy density of 9.29 W h/kg at a power density of 426 W/kg. Furthermore, the device demonstrated excellent cyclic stability, maintaining 78% of its capacitance after 10,000 cycles. These findings suggest that the device could be a viable option for various portable energy storage applications.