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

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 NaN₃ 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 NaN₃, a ZEZ N₈ precursor is also used. ZEZ N₈ was synthesized by the cyclic voltammetry method. EZE N₈ 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 N₈ 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.