Hydrothermally grown zinc oxide nanostructures@carbon composites for supercapacitor application

A simple approach for growing porous nanostructured zinc oxide (ZnO) and making its well-dispersed nanocomposite with activated carbon (AC) is demonstrated. Synthesis is done hydrothermally at 140 °C for 10 hours. X-ray diffraction (XRD), energy-dispersive X-ray (EDX), and scanning electron microscope (SEM) measurements confirm the formation of crystalline ZnO nanoparticles with flower-shaped morphology comprising clusters of nanopetals. ZnO and its composite with AC are used to fabricate symmetric hybrid supercapacitors. The electrochemical performance of ZnO electrode is compared to ZnO-AC composite electrode using 1 M Na${}_2$SO${}_4$ aqueous electrolyte. The electrochemical performance evaluated by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) demonstrates enhanced charge storage in ZnO-AC electrodes. The specific capacitance values of ZnO and ZnO-AC-based electrodes are found to be 214 and 298 F g${}^{-1}$ respectively at a current density of 1 A g${}^{-1}$ and the energy densities are 29.72 and 48.39 Wh kg${}^{-1}$ respectively at power density of 1 kW kg${}^{-1}$. The porous space between ZnO nanopetals and its high surface area geometry coupled with complementing properties of AC seems to facilitate a synergistic effect between ZnO's faradaic and AC's electric double-layer charge storage mechanisms, thus leading to enhanced specific capacitance with superior performance. (© 2022 Wiley‐VCH GmbH)