N₈ polynitrogen stabilized on multi-wall carbon nanotubes for oxygen-reduction reactions at ambient conditions

Polynitrogen (PN) species (N_n, n from 3 to 8) as highly energetic materials have attracted many theoretical calculations and predictions. N₃, N₄, N₅ or their ions were experimentally detected under high-pressure and high-temperature conditions. Herein, a N₈^- PN stabilized on the positively charged sidewalls of multi-walled carbon nanotubes (MWNTs) has been synthesized using cyclic voltammetry (CV) under ambient conditions. ATR-FTIR and Raman spectroscopic data assigned on the basis of density functional theory (DFT) calculations support the successful synthesis of a C₂h symmetry chain structure of the N₈ anion stabilized as MWNT^-N₈^-. Temperature programmed desorption (TPD) data show that MWNT⁺N₈^- is thermally stable up to 400°C. Oxygen-reduction reaction (ORR) experiments carried out using MWNT⁺N₈^- as the cathodic catalyst shows that it is very active for ORR with an even higher current density than that of a commercial Pt/carbon catalyst.