Sputtered manganese oxide thin film on carbon nanotubes sheet as a flexible and binder‐free electrode for supercapacitors

Summary In this work, flexible carbon nanotubes (CNTs)/manganese oxide (MnO 2 ) composite electrode was fabricated by direct deposition of MnO 2 nanoparticles on CNTs sheet by RF magnetron sputtering. The surface morphology and microstructure of the CNTs and CNTs/MnO 2 composite electrodes were characterized by X‐ray diffraction (XRD), scanning electron microscope‐energy dispersive spectroscopy (SEM‐EDS), X‐ray photoelectron spectroscopy (XPS), and Raman spectroscopy. It was found that 1‐μm thick MnO 2 film covered the surface of CNTs sheet with MnO 2 mass loading of 0.125 mg/cm 2 . CNTs/MnO 2 composite was tested as electrode materials for supercapacitors in sulfate media (1‐M H 2 SO 4 and Na 2 SO 4 ) by cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD). The results obtained showed that CNTs/MnO 2 composite electrode displayed good electrochemical performance in 1‐M Na 2 SO 4 , while the chemical stability of MnO 2 film was highly affected due its dissolution in acidic medium. A specific capacitance of 940 F/g was retained (with a capacitance retention of about 80%) after 3000 GCD cycles. CNTs/MnO 2 all‐solid symmetric supercapacitor using PVA/H 3 PO 4 gel electrolyte exhibited an initial specific capacitance 80 F/g and decreased by 25% after 3000 cycles.