Manganese dioxide (MnO2) promises for high-performance asymmetric suprecapacitors, owing to its high theoretical capacity, abundant source, and low cost. However, insufficient practically-achievable capacity and relatively narrow voltage window in alkaline electrolyte are blocking high energy density of MnO2-based supercapacitors, where strategies for activating its capacitive performance and widening voltage window are the top priorities to solve the bottleneck problems. Herein, both the fiber-in-tube (NCCM-FiT) and particle-in-tube (NCCM-PiT) nanostructures coulping active NiCoOx nanoparticles and conductive carbon with MnO2 tubes have been purposely fabricated, using the electrospun nickel cobalt oxides/carbon nanofibers (NCO/CNFs) as the self-template agents for enhanced energy density of MnO(2)based supercapacitors. These hierarchical hollow nanotubes with gradient pores and unique composi-tions yield excellent capacitive properties, in terms of a competitive capacity (431.7 F g(-1) or 431.7 C g(-1), 0.5 A g(-1)), which is 2.7 times that of the MnO2 nanotubes-based electrodes. A maximum energy density of 46.4 Wh kg(-1) is obtained at the power density of 400 W kg(-1) for the asymmetric device assembled with the NCCM-PiT-based positive electrode and the electrospun CNFs-based negative elec-trode. The remarkable energy density demonstrated by these hierarchical hollow nanotubes exemplifies a novel and effective design in electrode materials for the asymmetric supercapacitors (ASCs) with superior performance. (C) 2020 Elsevier Inc. All rights reserved.
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