Facilitated transport channels in carbon nanotube/carbon nanofiber hierarchical composites decorated with manganese dioxide for flexible supercapacitors

Freestanding carbon nanotube/carbon nanofiber (CNT/CNF) composites are prepared using electrospun CNFs as skeletons in a tubular chemical vapor deposition system. The obtained CNT/CNF composites show a hierarchical structure with a high special surface area, a high conductance (1250 S cm(-1) for a 10 mm x 20 mm sample), and a high flexibility. After coated with manganese dioxide (MnO2) via an in-situ redox deposition for 0.5 h (similar to 0.33 mg), the CNT/CNF/MnO2 electrodes show a high specific capacitance of 517 F g(-1) at a scan rate of 5 mV s(-1), which is about 5.6 time higher than that CNF/MnO2-0.25 h ones with MnO2 of similar to 0.36 mg. Moreover, this CNT/CNF/MnO2 electrodes show a much higher rate capability (57% at current density of 14 A g(-1)) than CNF/MnO2 ones (24% at 14 A g(-1)), and also show a higher cycling stability (maintaining 75% of the initial capacitance at cycle number of 1000). In addition, the symmetric supercapacitor assembled using two piece CNT/CNF/MnO2 electrodes shows their maximum energy density of 3.88 Wh kg(-1) at power density of 7000W kg(-1). The capacitance of the assembled capacitor maintains 70% after 100 bending cycles, indicating a good flexibility. These enhancements in EC performances should be due to our designed hierarchical structures. ft is suggested that such freestanding flexible CNB/CNT5/MnO2 hierarchical composites are highly promising for high-performance flexible supercapacitors. (C) 2014 Elsevier B.V. All rights reserved.