Arrays of nitrogen-doped carbon nanotubes (N-CNTs) have been grown on Si substrates by thermolysis of vapors of acetonitrile and ferrocene. To change the content of incorporating nitrogen, carbonyls of Mo, W, and Cr were added in the reaction mixture. The products were comparatively studied using electron microscopy, Raman scattering, X-ray photoelectron spectroscopy, and charge/discharge cycling in an acidic electrolyte. Electrochemical characteristics of N-CNTs were correlated with nanotube length and chemical state of nitrogen. It is found that pyridinic nitrogen has determining effect on the N-CNT performance at low scan rates of potential. The density functional theory calculations of N-CNT models reveal that protonation of pyridinic nitrogen induces a net of negative charges on the neighboring carbon atoms that could increase the electrode capacitance.
Cyclic voltammogram of nitrogen-doped carbon nanotube array at a scan rate of 2 mV s−1 in a 1 M H2SO4 aqueous solution and possible assignment of redox peaks.