Electrochemical Performance of Supercapacitors Based on ZnO/NiO@ Coconut Shell Activated Carbon Composite

Abstract A ZnO/NiO@CSAC (coconut shell activated carbon) composite was synthesized. The material exhibited high surface area (210.859 m²/g) and mesoporous structure, with a moderate pore volume of 0.135 m³/g and an average pore radius of 1.5474 nm. X-ray diffraction confirmed the crystallinity of ZnO and NiO with clear diffraction peaks at 2θ values of 31.8°, 34.5°, and 36.2°. Fourier-transform infrared spectroscopy revealed the functional groups such as Zn-O and Ni-O stretching vibrations, while Raman identified the peaks at 559 cm⁻¹ (ZnO) and 697 cm⁻¹ (defect-related modes). Field-effect scanning electron microscopy demonstrated a porous and heterogeneous morphology. Cyclic voltammetry showed the specific capacitance of 597 F/g at a scan rate of 5 mV/s, gradually decreasing to 210 F/g at 150 mV/s. The capacitance contribution increased with higher scan rates, reaching 97% at 150 mV/s. A total capacitance of 4226 F and a b-value of 0.38292 indicated a diffusion-controlled charge storage process. Galvanostatic charge/discharge curves confirmed the material’s high cycling stability with efficient ion and electron transport. Impedance spectroscopy revealed a low charge transfer resistance (1.566 Ω) and polarization resistance (1.067 Ω), high surface area, mesoporous structure, and favourable electrochemical properties make ZnO/NiO@CSAC a promising candidate for high-performance energy storage applications.