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

Highlights: • Hexagonal WO₃ nanorods are uniformly grown on MWCNT coated carbon cloth. • MWCNT-WO₃ hybrid exhibits high specific capacitance of 429.6 F g⁻¹ at 2 mA cm⁻². • MWCNT-WO₃ hybrid maintains 94.3% initial capacitance over 5000 cycles. • Flexible asymmetric supercapacitor shows high specific energy of 39.63 Wh kg⁻¹. -- Abstract: 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 hydrothermal treatment to deposit WO₃ nanorods on the MWCNT-coated carbon cloth. The MWCNT-WO₃ 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.