Layer-by-layer spray deposition and unzipping of single-wall carbon nanotube-based thin film electrodes for electrochemical capacitors

Spray deposited single-wall carbon nanotube (SWCNT) film electrodes comprising a randomly interconnected meso-porous network with high electrical conductivity and ionic mobility when immersed in an electrolyte have been investigated for applications in electrochemical capacitors. Layer-by-layer (LbL) spray deposition assembly of functionalised, oppositely charged (carboxylic COO− or amine NH3+) SWCNTs has been used to control the density and structure of sprayed electrodes, followed by vacuum and hydrogen heat treatment, and their electrochemical performance as a supercapacitor electrode assessed. Sprayed LbL SWCNT electrodes had faster charging and discharging kinetics than SWCNT-COOH electrodes, with a capacitance of 94 F g−1 compared with 63 F g−1 at 2 mV s−1 in a 1 M H2SO4 electrolyte; and LbL electrode capacitance was maintained to 91 F g−1 at 200 mV s−1. The capacitance of LbL SWCNT electrodes increased to 151 F g−1 at 2 mV s−1 after vacuum and H2 heat treatment that removed NH2 and COOH functional groups, and resulted in a hybrid microstructure of SWCNTs and multi-layer graphene sheets from unzipped SWCNTs.