Helically Coiled Carbon Nanotubes as Supercapacitor Electrodes*

Despite their low specific surface area (<500 m² g^-1) relative to that of activated carbon (1500-2000 m² g^-1), carbon nanotubes are attractive as effective electrode materials for supercapacitors due to their excellent electrical and mechanical properties. Electrodes comprised of arrays of helically coiled carbon nanotubes (HCNTs) and multi-wall carbon nanotubes (MWCNTs) were prepared and evaluated as novel electrode materials for electric double layer capacitors (EDLCs). While both types of electrodes exhibited a linear dependence on array height and a diffusion limited behavior below the 1 V s^-1 scan rate, the electrodes comprised of HCNT arrays exhibited a better performance.  Freestanding HCNT and MWCNT buckypapers were also prepared and used as electrodes, and the former showed a higher energy density relative to the latter with no loss in its power density and capacity fade. Collectively, this study concludes that HCNTs are well suited as binder-free electrodes that can be augmented with electroactive polymers for improved EDLC performance.