Nitrogen doped carbon nanotubes for dioxygen reduction from ab initio simulation

Nitrogen substitutionally doped short carbon nanotubes (CNTs) has potential application for metal-free efficient oxygen reduction reactions(ORRs). We have performed \textit{ab initio} density-functional-theory (DFT) calculations to simulate nitrogen substitutionally doped short (10, 0) CNTs. Our calculated results show that nitrogen prefers to stay at the open-edge of the short CNTs. Dioxygen O$_{2}$ can adsorb and partially reduce on the carbon-nitrogen complex site (Pauling site) and on carbon-carbon long bridge sites at the open-edge of the CNTs. The results of the spin polarization calculations show that the carbon atoms on the open-edge of the CNT can possess a magnetic moment of about 0.59 $\mu $B/atom, while those carbon atoms in the inner wall of the CNT do not have a magnetic moment. The doped nitrogen in the CNT does not have a magnetic moment. The chemisorption of dioxygen O$_{2}$ on the open-edge of the short CNT reduces the magnetic moments of the carbon atoms to nearly zero.