Freestanding composite electrodes of MnOx embedded carbon nanofibers for high-performance supercapacitors

Abstract

Manganese oxide/carbon nanofiber (MnO_x/CNF) composites were successfully fabricated as freestanding electrodes through incorporating different manganese sources of nanostructured MnO₂ or Mn(CH₃COO)₂·4H₂O into polyacrylonitrile (PAN) solution by electrospinning and a subsequent carbonization method. The MnO₂ with a rod-like hierarchical core–corona nanostructure was self-prepared by a hydrothermal method using polyvinylpyrrolidone (PVP) to control the size and morphology of nanoparticles. The morphologies and structures of the MnO_x/CNF composites were characterized by means of field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. MnO_x/CNFs produced from Mn(CH₃COO)₂·4H₂O exhibited good flexibility with uniform dispersion of small MnO_x particles in the loose structures of the CNFs. In contrast, MnO_x/CNFs derived from MnO₂ displayed relative brittle mechanical properties. The electrochemical performances of the two composites were investigated by cyclic voltammetry, galvanostatic charging/discharging and impedance measurement techniques. The resulting MnO_x/CNFs demonstrated excellent electrochemical performance with great rate capability, low internal resistance and long-term cycling stability. Composites produced from Mn(CH₃COO)₂·4H₂O delivered a specific capacitance of 211 F g⁻¹ at 0.25A g⁻¹ in 0.5 M Na₂SO₄ electrolyte These results suggest that such freestanding MnO_x/CNF composites would be promising electrodes for high-performance supercapacitors.