Smart and flexible supercapacitor based on a porous carbon nanotube film and polyaniline hydrogel

Smart and flexible supercapacitors are of ever increasing importance for energy-storage devices. Herein, a simple and effective strategy to make a supercapacitor in a “flexible” and “electrochromic” way was based on the direct and convenient immobilization of a polyaniline (PANI) hydrogel onto a porous carbon nanotube (CNT) film. The resultant symmetric all-solid-state supercapacitor showed a favorable specific capacitance of 315 F g−1 and a relatively high cycling stability (92% capacitance retention after 1500 cycles). The bending test indicated that the obtained supercapacitor was flexible and its performance was only decreased by less than 7.0% after 150 bending cycles with a bending angle of 180°. Furthermore, the supercapacitor displayed a rapid and reversible chromatic transition between different working stages, and its level of stored energy could be quickly determined by the naked eye in a predictable and noticeable manner. This work may open a simple and convenient avenue for the fabrication of smart, flexible and all-solid-state supercapacitors.