Freestanding functionalized carbon nanotube-based electrode for solid-state asymmetric supercapacitors

Recently, many attempts have been made to increase the specific capacitance of carbon nanotubes (CNTs). Chemical enhancement by adding redox active functional groups on CNTs increases the specific capacitance, while excessive oxidation decreases conductivity and leads to poor cycle life. Here we report the electrochemical enhancement methods followed by annealing at different temperatures in air to add and adjust the redox active functional groups on freestanding CNT films. Functionalized freestanding CNT films were used as positive electrodes, assembled with freestanding CNT/MoO3-x negative electrodes to fabricate carbon nanotube-based solid-state asymmetric supercapacitors (ASCs). The whole device showed a high volumetric capacitance of 3.0 F cm(-3), energy and power density of 1.5 mWh cm(-3) and 4.2 W cm(-3), respectively. We also fabricated a SCs pack to drive a homemade wireless transport system successfully, demonstrating the potential applications of this solid-state system for portable/wearable electronics. (C) 2014 Elsevier Ltd. All rights reserved.