High areal capacitance of Fe3O4-decorated carbon nanotubes for supercapacitor electrodes

A conceptually new approach has been developed for the fabrication of magnetite (Fe3O4)-decorated carbon nanotubes (M-CNTs) for negative electrodes of electrochemical supercapacitors. M-CNTs were prepared by an ultrasonic-assisted chemical synthesis method, which involved dispersion of functionalized CNTs in water, Fe3O4 formation on the CNTs surface, and particle extraction through liquid-liquid interface (PELLI). Palmitic acid was found to be an efficient new extractor for PELLI. The slurries produced after drying and redispersing M-CNTs and slurries obtained using PELLI were used for electrode fabrication. The electrodes prepared using PELLI showed superior performance due to reduced particle agglomeration. Testing results provided an insight into the influence of Fe3O4/CNTs mass ratio on the capacitance and capacitance retention at high charge-discharge rates. A capacitance of 5.82 F cm-2 (145.4 F g(-1)) was achieved in Na2SO4 electrolyte using electrodes with high active mass of 40 mg cm(-2) and ratio of active mass to current collector mass of 0.6. Good electrochemical performance was achieved at low impedance. The capacitance of the negative M-CNTs electrodes was comparable with capacitance of advanced positive MnO2-CNTs electrodes, which was beneficial for the fabrication of asymmetric devices. The asymmetric device has been fabricated, which showed promising performance in a voltage window of 1.6 V.