Achieving high-energy-density crown-like polymeric nitrogen cr-N via chelate CeN₈

Polymeric nitrogen materials are the crown of high energy density materials due to their environmental friendliness. Here, we proposed a general strategy to achieve crown-like polymeric nitrogen (cr-N) by combining high-pressure and chemical exfoliation methods. Using the first-principle structure search, we demonstrated that the cerium (Ce) atoms can effectively open the N≡N bond of N₂ at a moderate pressure of 25.7 GPa, and then the layered chelate P1¯-CeN₈ with the crown-like N₁₈ ring is formed via the ligand effect of metallic Ce. Interestingly, when released to ambient conditions, P1¯-CeN₈ can still maintain good stability due to robust N–N bonds; meanwhile, the interaction strength between the Ce atoms and N₁₈ ring decreases. As a result, Ce atoms can be selectively removed by alkaline anions, and the dynamic progresses are presented, which is similar to the synthesis of MXenes via the alkali intercalation exfoliation method, and then crown-like polymeric nitrogen cr-N is formed. The cr-N is proved to be dynamically, mechanically, and thermally stable at ambient conditions. Moreover, the excellent gravimetric energy density, detonation pressure, and detonation velocity of cr-N make it a significant high-energy density material. This work opens a new general avenue to realize polymeric nitrogen via high-pressure and chemical exfoliation methods.