Synthesis and Stabilization of Cubic Gauche Polynitrogen under Radio-Frequency Plasma

Abstract

Cubic gauche polynitrogen (cgPN) has been very attractive because of its high energy density that is 3.5 times of the TNT energy. cgPN has been investigated theoretically in detail, but few experimental studies have been reported. In 2004, cgPN was first synthesized from nitrogen gas under extremely high temperature and high pressure conditions and the trace amount of cgPN in the high-pressure vessel decomposed once the pressure was released. Until recently, our group for the first time synthesized cgPN from an NaN 3 precursor under ambient conditions with radio-frequency plasma. Here, synthesis and stabilization of cgPN are systematically investigated both computationally and experimentally. The effects of several major factors are studied, and the possible key intermediate is explored. In addition to NaN 3 , a ZEZ N 8 precursor is also used. ZEZ N 8 was synthesized by the cyclic voltammetry method. EZE N 8 is found to be the potential intermediate for cgPN formation based on the Fourier transform infrared and Raman spectra and the fact that a higher yield of cgPN is obtained with the ZEZ N 8 precursor. Na + is shown to stabilize cgPN under ambient conditions; however, an excess of Na + has a negative effect on cgPN growth. The oxygen reduction reaction (ORR) was carried out using cgPN as the cathodic catalyst, and the result shows that it is very active for the ORR, which is comparable with a commercial Pt/carbon catalyst. Moreover, cgPN shows an excellent stability during the ORR. This work guides the rational synthesis and scaleup of cgPN and its practical applications for the ORR.

Polynitrogen High Energy Density Materials Synthesized by Nonequilibrium Plasma

“…In a follow-up detailed study in 2022 from the same group, Zhuang et al reported on a similar system. They explored both carbon nanotube-supported and unsupported NaN 3 , as well as N 8 – precursors . Vibrational spectroscopy again, combined with diffraction and density functional theory simulations, supported the claim of radiofrequency nitrogen plasma synthesis of the cubic gauche polymorph of polynitrogen at ambient pressure.…”

“…The authors have presented some interesting electrochemical behavior of the materials. 34 The reported preliminary evidence suggests that there probably needs to be a condensed phase precursor involved in the synthesis of polynitrogen compounds by nonequilibrium plasma (Figure 6). This condensed phase is expected to serve two purposes: (1) it hosts the pentazolate compound, which is expected to be a condensed phase, mixed into a condensed phase, or on the surface of a condensed phase, and (2) it keeps the pentazolate temperature low to prevent thermal decomposition.…”

“…The group at the New Jersey Institute of Technology has also published a series of papers on the synthesis of polynitrogen compounds supported and unsupported by carbon nanotubes from NaN 3 as well as electrochemically prepared N 8 – . − Benchafia et al reported in 2017 on the radiofrequency plasma synthesis near ambient pressure of a material, using sodium azide and nitrogen gas as precursors, which showed vibrational spectra and diffraction patterns consistent with the cubic gauche polymorph of polynitrogen . The authors bring an important point to the fore, which is the role of a support in stabilizing polynitrogen species.…”

“…Ga 2 O 3 by controlling the interaction of the material with the plasma during synthesis. , Since plasmas can produce a chemically reactive environment at low temperature involving the excitation of N 2 gas and are capable of synthesizing, under vacuum, phases that are usually only observed at high pressure, plasmas are therefore attractive for the synthesis of polynitrogen HEDMs. Indeed, there have already been some early movers in the area, and promising results have been obtained. − The field remains very much open, and breakthroughs surely await therein.…”

A polymeric nitrogen N$$_6$$–N$$_2$$ system with enhanced stability at low pressure

“…For instance, the temperature and pressure requirements for diamond synthesis are as high as (30120 GPa, 1000–3000K) with shock waves, (15 GPa, 3000 -3500K) with HPHT, (5–10 GPa, 1500–2000K) with catalytic HPHT and (<1 GPa, <1500K) with plasma CVD 45 . The experimental work conducted in our group to synthesize the cubic gauche by plasma CVD is an example of the efforts within the scientific community to synthesize polymeric nitrogen compounds despite their metastability at ambient conditions 31 , 46 . Another key factor for a potential synthesis of a polynitrogen is a high energy lattice structure which has the capability of acquiring enough cohesive energy to overcome metastability.…”