MWCNT incorporated wool-ball-like CuO@NiO hybrid nanostructures for high-performance energy storage device

Abstract

In the present work, some CuO@NiO@MWCNT (CNC) ternary hybrid nanostructures have been synthesized solvothermally in a well-controlled manner by varying the amount of MWCNT for energy storage application with superior electrochemical performance. Among three CNC1 (CuO@NiO:40 mg MWCNT), CNC2 (CuO@NiO:40 mg MWCNT; in one-step method) and CNC3 (CuO@NiO:60 mg MWCNT) nanocomposites, the CNC1 has emerged out with the best performance due to its well-designed components and synergistic effects, wool ball-like morphology and a mesoporous structure containing more active sites, a shortest conductive pathway for electron-ion transportation. The CNC1 hybrid with a highly ordered mesoporous structure (pore radius ~1.9 nm) offers a high specific surface area of 262 m2 g−1. The structure and microstructure of these ternary hybrid nanocomposites are characterized by analyzing respective X-ray diffraction patterns, HRTEM, FESEM images, and XPS spectra. HRTEM and FESEM images reveal the uniform distribution of the MWCNT network and the growth of spherical NiO nanoparticles of 8–10 nm in these CNT. The optimized ternary wool ball-like CNC1sample exhibits a high specific capacitance of 786 F g−1 and high areal capacitance of 3.144 F cm−2at a current density of 0.6 A g−1 with a significant rate capability. A two-electrode asymmetric device has been designed with the CNC1 sample as the positive electrode and activated carbon as the negative electrode in a 1 M Na2SO4 electrolyte medium. This device offers maximum specific energy of 32.21 Wh Kg−1, a maximum power density of 3923 W Kg−1, excellent cyclic stability and a high Coulomb efficiency. The optimum use of MWCNT in CNC1 ternary nanostructures results in better morphology, leading to a significant reduction in charge transfer parameters,as revealed by EIS spectroscopy.