Rational Synthesis of Polymeric Nitrogen N₈^– with Ultraviolet Irradiation and Its Oxygen Reduction Reaction Mechanism Study with In Situ Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy

Abstract

Polynitrogen (PN) deposited on multiwalled carbon nanotubes was synthesized by cyclic voltammetry with ultraviolet (UV) irradiation. Compared to the sample formed without UV, a larger amount of N8 – was synthesized and was found to distribute more uniformly on the MWNTs with 254 nm UV irradiation, indicating that the production of more azide (N3)0 radicals as the precursors for synthesis of N8 – by photoexcitation of azide (N3 –) ions is a rate-limiting step for PN synthesis. An oxygen reduction reaction kinetics study indicated a four-electron reaction pathway on N8 –, whereas a two-electron process occurs on N3 –. Analysis by in situ shell-isolated nanoparticle-enhanced Raman spectroscopy revealed that the side-on and end-on O2 adsorption occurred at N8 – and N3 –, respectively, confirming the electron transfer process. A full direct-methanol fuel cell study shows that methanol crossover typically reduces the current density of Pt/C by ∼40% but has very little effect on the performance of the PN-MWNT catalyst after testing for 120 h. Moreover, the power density from the PN-MWNT cathode is at least twice that from a Pt/C cathode.

All-Nitrogen Energetic Material Cubic Gauche Polynitrogen: Plasma Synthesis and Thermal Performance

“…This result indicates that cg-N/CNT has superior thermal stability to the other two samples and a similar decomposition temperature to that determined using temperature programmed desorption (TPD) by Zhuang et al [ 37 ]. Theoretical calculations suggest that carbon nanotubes stabilize polynitrogens, such as N 8 oligomers [ 35 ], and may also contribute to the high thermal decomposition temperature of cg-N.…”

“…A series of nitrogen clusters, such as TiN 12 + [ 30 ], ZrN 12 + [ 31 ], VN x + (x = 8, 9, 10) [ 32 ], and LiN x + (x = 2, 4, 6, 8) [ 33 ], have been obtained by laser ablation of nitrogen-rich compounds. Cyclic voltammetry (CV) has been used to synthesize polynitrogen N 8 − ions on pristine and boron-doped graphene, as well as on multiwalled carbon nanotubes (CNTs) [ 34 , 35 ]. The use of plasma-enhanced chemical vapor deposition (PECVD) to produce cg-N has opened an avenue for the synthesis of cg-N under ambient conditions [ 36 , 37 ].…”