Carbon nanotubes coated with a nitrogen-doped carbon layer and its enhanced electrochemical capacitance

Nitrogen-doped carbon layer coated carbon nanotubes (NC-CNTs) were prepared by using a simple two-step procedure of in situ polymerization of pyrroles onto CNTs and subsequent carbonization, without using template removal and activation treatment. Structure and composition analyses show that in situ polymerization results in the formation of CNTs coated with a polypyrrole layer (CNTs@PPy), by following carbonization process which is converted into the NC-CNTs with nitrogen content of 8.6 at%. N2 adsorption–desorption isotherms reveal that the NC-CNTs have not only much larger specific surface area (SSA) than that of the CNTs but also a hierarchical pore structure consisting of micropores, mesopores and macropores. Owing to the combination effect of abundant nitrogen containing groups and improved pore structure, the NC-CNTs electrode without conducting additives exhibits much higher capacitance (205 F g−1) than the CNTs electrode (25 F g−1) and excellent cycling stability in 6 M KOH electrolyte, although the NC-CNTs has only moderate SSA of 197 m2 g−1. The easy preparation and smart electrochemical performance of NC-CNTs makes it a promising electrode material for supercapacitors.