Direct growth of WO3 nanostructures on multi-walled carbon nanotubes for high-performance flexible all-solid-state asymmetric supercapacitor

The rational design and development of highly conductive hierarchical nanostructured materials are of great importance to improve the electrochemical performance of supercapacitors. Great efforts have been committed to the development of positive electrodes for asymmetric supercapacitors (ASC). However, it is still necessary to develop better negative electrodes for practical applications. In present investigation, a multi-walled carbon nanotubes-tungsten trioxide (MWCNT-WO3) hybrid nanostructure is prepared as a negative electrode for ASC. The MWCNT-WO3 hybrid electrode is prepared using a simple two-step approach, which involves coating of MWCNTs on carbon cloth substrates followed by hydro-thermal treatment to deposit WO3 nanorods on the MWCNT-coated carbon cloth. The MWCNT-WO(3)hybrid electrode exhibits a maximum specific capacitance (areal capacitance) of 429.6 F g(-1) (1.55 F cm(-2)) and capacity retention of 94.3% after 5000 cycles, which are higher than the 155.6 F g(-1) (0.43 F cm(-2)) and 84.9% shown by pristine WO3 in 1 M LiClO4 electrolyte. A flexible all-solid-state ASC is self-assembled with MWCNT-WO3 as a negative electrode, MnO2 as a positive electrode, and PVA-LiClO4 as a gel electrolyte. The MnO2//MWCNT-WO3 ASC achieve specific capacitance of 145.6 F g(-1) at a current of 2 mA and specific energy of 39.63 Wh kg(-1) at a specific power of 546 W kg(-1). Specifically, the ASC exhibits superior long-term cycling stability (77% over 10000 cycles) and excellent mechanical flexibility with less capacitance loss. These remarkable results demonstrate the potential of using MWCNT-WO3 hybrid nanostructures for the fabrication of high-performance energy storage devices. (C) 2019 Published by Elsevier Ltd.