Helically coiled carbon nanotube electrodes for flexible supercapacitors

Abstract

Novel highly flexible electrodes consisting of helically coiled carbon nanotubes (HCNTs) have been developed for flexible supercapacitors (SCs). Hierarchically mesoporous HCNTs are synthesized on unidirectional carbon fiber (UCF) by catalytic chemical vapor deposition. Free-standing HCNTs grown on UCF (HCNTF) is further used as electrode cum current collector for fabricating flexible SCs. Highly bendable UCF serves both as the substrate for the synthesis of HCNTs and as current collector for the SC. No separate secondary current collector is used in this study. The microstructure and surface morphology of the HCNTF hybrid is characterized by scanning electron microscopy and transmission electron microscopy, the chemical structure is determined by Raman spectroscopy, the chemical bonding states are examined by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy and the surface area is measured by Brunauer–Emmett–Teller surface area measurement. The electrochemical properties of HCNTF SC are examined by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge measurements. The HCNTF hybrid exhibits open mesoporous nanostructure with an average pore size of 3.8 nm. The bendability of HCNTF SC is tested by carrying out the galvanostatic charge/discharge measurement by bending the SC at different angles and the study reveals that the SC is highly bendable. The HCNTF SC exhibits a maximum gravimetric capacitance of 125.7 F g−1 with an area specific capacitance of 145.3 mF cm−2 at a current density of 0.28 mA cm−2. The supercapacitive performance of the HCNTF SC is found to be superior to that of the SCs utilizing straight-CNTs based electrodes. The present study opens-up the successful development of novel carbonaceous electrode with helical nanostructure for application particularly in SCs.