Plant mediated-green synthesis of ZnO nanoparticles as a high capacitance electrode for supercapacitor applications

As a result of its cost-effectiveness and eco-friendliness, the green-synthesised supercapacitor electrodes were gaining much attention in energy storage applications. Due to its versatile properties, Zinc Oxide (ZnO) is a specialised material in supercapacitor applications. In this research work, pure ZnO nanoparticles (ZnO NPs) and Citron (CT) fruit peel extract solution added ZnO nanoparticles (ZnO–CT NPs) were prepared via co-precipitation technique followed by a thermal annealing method. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDAX), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR) and Ultraviolet–Visible Diffuse Reflectance Spectroscopy (UV-Drs) confirmed the physico-chemical and optical properties of as-prepared ZnO and ZnO–CT NPs. The obtained pure ZnO NPs and ZnO-CT NPs coated supercapacitor electrodes were analysed for the charge storage activities in an aqueous electrolyte solution. As a result, the ZnO-CT electrode achieves the capacitance of ~ 2032 F g⁻¹ at the current density value of 4 A g⁻¹, which is higher than pure ZnO capacitance of ~ 1040 F g⁻¹. Further, this electrode attained a superior stability retention of 90% in 1500 Galvanostatic Charge/Discharge (GCD) cycles. This work demonstrates that the renewable route approach to synthesise ZnO nanoparticles was considered a potential material towards green energy storage technology.