Highly conductive electrospun carbon nanofiber/MnO2 coaxial nano-cables for high energy and power density supercapacitors

► Highly conductive carbon nanofibers are used as the support backbone for MnO2 for supercapacitor electrode. ► The correlation of the carbon nanofibers/MnO2 electrode conductivity and the electrochemical performance is investigated. ► The carbon nanofibers/MnO2 coaxial nanostructure shows enhanced specific capacitance up to 1.1Fcm−2 and 311Fg−1. This paper presents highly conductive carbon nanofiber/MnO2 coaxial cables in which individual electrospun carbon nanofibers are coated with an ultrathin hierarchical MnO2 layer. In the hierarchical MnO2 structure, an around 4nm thick sheath surrounds the carbon nanofiber (CNF) in a diameter of 200nm, and nano-whiskers grow radically outward from the sheath in view of the cross-section of the coaxial cables, giving a high specific surface area of MnO2. The CNFs are synthesized by electrospinning a precursor containing iron acetylacetonate (AAI). The addition of AAI not only enlarges the specific surface area of the CNF but also greatly enhances their electronic conductivity, which leads to a dramatic improvement in the specific capacitance and the rate capability of the CNF/MnO2 electrode. The AAI-CNF/MnO2 electrode shows a specific capacitance of 311Fg−1 for the whole electrode and 900Fg−1 for the MnO2 shell at a scan rate of 2mVs−1. Good cycling stability, high energy density (80.2Whkg−1) and high power density (57.7kWkg−1) are achieved. This work indicates that high electronic conductivity of the electrode material is crucial to achieving high power and energy density for pseudo-supercapacitors.