Effects of CNT‐film Pretreatment on the Characteristics of NiCo2O4/CNT Core‐shell Hybrids as Electrode Material for Electrochemistry Capacitor

Abstract

AbstractNiCo2O4/CNT nanocomposite films were fabricated by in‐situ growing ultrafine NiCo2O4 nanoparticles on acid‐modified carbon nanotube (CNT) films. The effects of CNT‐film pretreatment were investigated thoroughly by various characterization outfits including Fourier Transform Infrared spectroscopy (FT‐IR), X‐ray photoelectron spectroscopy (XPS), Raman spectroscopy, RTS‐9 four‐point probes resistivity measurement system, X‐ray powder diffraction (XRD), scanning electron microscopy (SEM) and CHI660D electrochemical workstation. These results suggested that carbon nanotubes were uniformly wrapped by NiCo2O4 nanoparticles forming a hierarchical core‐shell structure. And the crystallinity, conductivity of the CNTs and detail structure (both morphology and size) of the NiCo2O4 nanoparticles varied with prolonged acid treatment time which resulted in increased functional groups and defects on CNT films and further affected the electrochemical properties. The composite film composed of the CNT film pretreated by mixed acid for 12 h exhibited excellent electrochemical properties: 828 F/g at 1 A/g and 656 F/g at 20 A/g, and maintained over 99 % of its capacitance after 3000 cycles of charge/discharge at 5 A/g. Acid treatment for either too long or too short is detrimental to the electrochemical properties of the composite films. Such work should be of fundamental importance for tailoring electrochemical properties by elaborate design of acid treatment on CNTs.