Supercapacitor performance of binder-free buckypapers from multiwall carbon nanotubes synthesized at different temperatures

Multiwall carbon nanotubes (MWCNTs) have been synthesized by aerosol-assisted catalytic chemical vapor deposition method from a 2% ferrocene solution in toluene at temperatures of 720 and 800 degrees C. After an oxidation by a HNO3/H2SO4 mixture, MWCNTs were dispersed in water and deposited in form of buckypapers with a thickness of approximate to 150m. The obtained materials were used as working electrodes of supercapacitors without adding of binder. The electrode from MWCNTs synthesized at lower temperature showed the larger capacitance in 1M H2SO4 and 6M KOH electrolytes, especially at low scan rates. An increase of double-layer capacitance was due to larger specific surface and microporosity of the material; a gain in pseudocapacitance was attributed to larger quantity of oxygenated groups developed on the defective surface of nanotubes. The electrode showed a good cyclic performance during a repetitive charge/discharge test. A larger specific capacitance of MWCNTs synthesized at 720 degrees C is related with etching of nanotube tips and higher oxygenation of nanotube surface as the result of binder-free buckypaper electrode preparation.