Effect of pyrrolic-N defects on the capacitance and magnetization of nitrogen-doped multiwalled carbon nanotubes

Abstract

Heteroatoms in multiwalled carbon nanotubes modify their chemical reactivity and electronic properties. Nitrogen as a doping element changes the morphology by boosting the surface area, the density of defects, electronic states, and chemically actives sites that improve the electrocatalytic activity and other properties. Nitrogen defects create mainly the pyridinic, pyrrolic, and quaternary-N configurations presenting different localized electronic configurations. This work outlined and studied the distribution and physicochemical properties of N-doped multiwalled carbon nanotubes as a function of the temperature profile along a CVD reactor. X-ray photoelectron spectroscopy demonstrated that the nitrogen content is maximal in the second furnace high-temperature zone, and the pyrrolic-N doping predominate. The ID/IG ratio from Raman spectroscopy increases in this zone, revealing a defective graphitic material. The cyclic voltammetry showed that the specific capacitance increases for pyrrolic-N from the last three-quarters of the reactor due to the augment of active carbon atoms associated with pyrrolic-N defects and the chemical decomposition of nitrogen precursor alongside the reactor. Theoretical calculation on the electronic properties and potential electrostatic surface of carbon nanotubes suggests the surface metallicity when pyridinic-N and quaternary-N are dominant and active sites for possible hydrogen or oxygen binding when pyrrolic-N are prevalent.