Achieving ultrahigh energy density and excellent stability in carbon pentazole

Abstract

Binary CN compounds received considerable interest in green energy and sustainable materials. However, the energy density and structural stability at the ambient conditions are usually mutually exclusive in high-nitrogen CN materials. In this work, CN₂₀ is identified via ab initio evolutionary searches at 35 GPa, termed as P2₁c-C(N₅)₄, in which carbon is only 4.11% in mass fraction but can provide enough electrons to stabilize the aromatic cycle-N₅⁻ anions. The results show that P2₁c-C(N₅)₄ exhibits excellent thermodynamic and dynamic stability under the synthesis pressure, and the robust covalent structure of P2₁c-C(N₅)₄ can be maintained under ambient conditions while releasing the pressure. The electronic structures indicate that P2₁c-C(N₅)₄ possesses high chemical inertness because of its non-absorption of visible light with a well-proportioned charge distribution. In addition, the decomposition of P2₁c-C(N₅)₄ can release an energy of 6.53 kJ g⁻¹, which, to our knowledge, is the highest recorded among room-temperature stable binary nitrogen-rich compounds. The energy released can be further improved to 11.13 kJ g⁻¹ under an oxygen-rich environment. Moreover, the detonation pressure of P2₁c-C(N₅)₄ is up to 44.76 GPa, which is similar to that of a potential rocket propellant. In light of these hallmarks, P2₁c-C(N₅)₄ is a promising low cost and environmentally friendly high energy density material.