Doping and electrochemical capacitance of carbon nanotube-polypyrrole composite films

Composite films were electrochemically synthesised via the simultaneous deposition of multiwalled nanotubes and polypyrrole, a conducting polymer. Negatively charged functional groups attached to the surface of the acid treated nanotubes enables the tubes to act as a dopant for the PPy in these films. Scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy revealed that the nano-porous three-dimensional arrangement of PPy coated MWNTs in these films produced specific capacitances per mass and geometric area as high as 192 F g(-1) and 1.0 F cm(-2), respectively. This value of specific capacitance per geometric area exceeds that of both component materials and other carbon nanotube-conducting polymer composites. The composite films described in this report were also able to charge and discharge more than an order of magnitude faster than similarly prepared pure PPy films. The nano-porosity and small diffusion distances within the composite films, crucial to achieving the superior capacitive performance, were found to be dependent on the concentration of nanotubes and additional dopant anions in the polymerisation electrolyte, offering possibilities for tailoring of the composite structure.