Capacitive behaviour of functionalized carbon nanotube/ZnO composites coated on a glassy carbon electrode

Abstract

An efficient and simple method has been developed to synthesize functionalized multiwall carbon nanotube (FCNTs)/ZnO composites which are employed as supercapacitor (SC) materials. The multiwall carbon nanotubes (MWCNTs) are oxidised in the presence of concentrated HNO₃ at 120 °C for 2 h to generate oxygenated functional groups on the tube-ends along with the side walls of FCNTs to enhance their inherent capacitance. The synthesis of FCNTs/ZnO composites has been carried out by solvothermal decomposition of a single source precursor (SSP), ZnCl₂(benzscz)₂ (benzscz = benzaldehyde semicarbazone). The FCNTs/ZnO composites are well characterized by different techniques viz. X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) etc. The FCNTs/ZnO/glassy carbon (GC) electrodes are fabricated by the deposition of FCNTs/ZnO composites on the surface of GC which are further tested for their electrochemical performances by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronopotentiometry. The FCNTs/ZnO composite electrodes show better reversible charging/discharging ability and higher capacitance values compared to bare FCNTs and ZnO electrodes due to the synergistic effect of FCNTs and ZnO. Results show that the composite FZ-1 (FCNTs/ZnO (1 : 1)) displays higher capacitance (157 F g⁻¹), maximum energy density (32.15 W h kg⁻¹) and good cycle stability. It retains over 96% of its initial specific capacitance even after 1000 cycles.