Preparation of a Three-Dimensional Ordered Macroporous Carbon Nanotube/Polypyrrole Composite for Supercapacitors and Diffusion Modeling

Three-dimensional ordered macroporous (3DOM) carbon nanotube (CNT)/polypyrrole (PPy) composite electrodes for supercapacitor application were prepared through cyclic voltammetric copolymerization from a solution containing both acid-treated CNTs and pyrrole monomers. A self-assembled SiO2 colloidal crystal was used as the sacrificial template. After electrochemical copolymerization, the template was removed, and a 3DOM CNT/PPy composite electrode was obtained. The specific capacitance of the composite reached 427 F g(-1) at the scanning rate of 5 mV s(-1), and it is calculated that ion diffusion contributed approximately 30% to the specific capacitance of the composite. A mathematical model of mass transport was proposed to evaluate the ion diffusion capability on the surfaces of 3DOM, nanoporous, and planar films. The calculation results showed that the flux (i.e., ion flux per unit length) of 3DOM film was larger than that of planar film, while the flux of nanoporous film was close to that of planar film. The model indicates that 3DOM film is favorable for ion transportation, while nanoporous film does the opposite. The model partially explains the reason why the specific capacitance of the prepared 3DOM CNT/PPy composite is far above the specific capacitance values of other reported CNT/PPy composites, even the nanoporous CNT/PPy composite.