Structural control of highly oxidized carbon nanotube networks for high electrochemical performance

Abstract

Carbon nanotubes (CNTs) are one of the most suitable candidates for electrochemical applications because of their high electrical conductivity and large specific surface area. However, the bundling behavior of single-walled CNTs (SWCNTs) due to π–π interaction limits their solution processability and structural control. Herein, we report a fabrication method for highly conductive and porous CNT network films exhibiting a high electrochemical performance in aqueous media. This was achieved through the filtration of a dispersant-free dispersion of oxidized carbon nanotubes by less defective chlorate-based oxidation and thermal deoxygenation in air. To increase the proportion of mesopores in the film, oxidized long multi-walled CNTs (Ox-LMWCNTs) were incorporated into Ox-SWCNT networks. The Ox-SWCNT/Ox-LMWCNT (1/1 wt.%) hybrid film exhibited a large surface area of 492 m2/g, which decreased to 225 m2/g after thermal treatment at 200 °C in air with increasing electrical conductivity up to 29,500 S/m. In particular, the proportion of mesopores increased from 65 to 89%. The enhanced electrochemical capacity of the hybrid films (147 F/g and 99% retention at 10 A/g) could be attributed to the increased mesopores and enhanced electrical conductivity of LMWCNTs after thermal deoxygenation even in air.