Optimizing the Cu 2+ ions and carbon-related defect centers ratio in g-C 3 N 4 -ZnO:Cu nanocomposites for supercapacitor applications †

Abstract

In this work, we synthesised a composite material based on g-C 3 N 4 as a carbon source and ZnO doped with different Cu ion concentrations (ZnO:Cu x, x = 0, 0.2, 0.4, 0.6, 0.8, and 1%) using multiple synthesis approaches. The synthesized g-C 3 N 4 -ZnO:Cu nanocomposites were characterised using advanced techniques like X-ray diffraction, scanning and transmission electron microscopy, Fourier transform infrared spectroscopy, and UV-Vis adsorption and photoluminescence spectroscopy to evaluate the formation of the composite structure and the role of the dopant on the morpho-structural, optical, and compositional properties. Electron paramagnetic resonance and X-ray photoemission spectroscopy were employed to determine the defect structure of the composite materials, the presence of Cu ions in the ZnO lattice, and the oxidation state of the Cu ions. Electrochemical measurements, including galvanostatic charge-discharge and cycling stability tests, confirmed superior charge storage capacity, efficient electron transfer, and long-term durability. Notably, the g-C 3 N 4 -ZnO:Cu0.8-based supercapacitor device exhibited excellent cycling stability with 110% capacitance retention after 10,000 cycles, along with the highest power (917.81 W/kg) and energy density (25.24 Wh/kg) values, making it a promising candidate for high-performance energy storage applications.