Microwave synthesis of titania-coated carbon nanotube composites for electrochemical capacitors

Herein reported is a new strategy for rapid synthesis of TiO2 nanocrystals onto carbon nanotubes (CNTs) for high-power and high energy-density electrochemical capacitors (ECs). The synthesis method consists of chemical-wet impregnation and pulse microwave deposition at 40 degrees C within a short period of 10 min. Highly-crystalline TiO2 crystals with average size of 10-20 nm are dispersed onto the surface of CNTs, forming the TiO2/CNT flexible electrode. The capacitive behavior of TiO2/CNT capacitors is well characterized by cyclic voltammetry and charge-discharge cycling. A ca. 137% increase in capacitance is achieved through the decoration of TiO2 on CNTs, e.g., an increase from 76.5 to 176.5 F g(-1) at a current density of 0.2 A g(-1). This improved capacitance can be attributed to the fact that the decoration of TiO2 is capable of raising the hydrophilic surface fraction of electrode which is accessible for the formation of electric double-layer in acidic electrolyte, as compared to fresh CNT electrode. The TiO2 nanocrystals also serve as redox sites for the pseudo-capacitance. As analyzed by the Ragone plots, the energy density of TiO2/CNT capacitor can reach as high as 5.6 Wh kg(-1) at a power density of 6428 Wh kg(-1). (C) 2014 Elsevier B.V. All rights reserved.