Nitrogen doped carbon nanotubes and nanofibers: Composition, structure, electrical conductivity and capacity properties

Structurally different nitrogen doped nanotubes and nanofibers (N-CNTs and N-CNFs) synthesized by a standard method of decomposing ethylene-ammonia mixtures on metal catalysts were studied. In N-CNTs the uniform distribution of nitrogen and the formation of the ordered defects were registered. The ordered defects comprise four carbon vacancies and pyridine-like nitrogen, according to the performed structural simulation. On the contrary, N-CNFs were found to have the non-uniform distribution of nitrogen; their structural defects are disordered and also contain the pyridine-like nitrogen. An increase in the nitrogen content in N-CNTs, and hence in the amount of ordered defects, leads to a monotonic decrease in conductivity. For N-CNFs the dependence of conductivity on the nitrogen content is non-monotonic and is characterized by the extremum due to the competition of electron doping and structure disordering. A similar enhancement of the electrode capacity with raising the nitrogen content both in N-CNTs and N-CNFs was observed and explained by improved hydrophilic properties of the nitrogen doped carbon nanomaterials.