P1-C7N4O8: improved stability and energy density via a covalent framework with uniform single bonds

Abstract

Energy can be stored in the chemical bonds of CNO energetic materials. However, non-uniform chemical bonds hinder the trade-off between structural stability and energy density: strong chemical bonds reduce energy density, whereas weak bonds lower the decomposition barrier. We propose a 3D close-packed structure of P1-C₇N₄O₈ with uniform chemical single bonds using a first-principles crystal structure search method. The results show that P1-C₇N₄O₈ formation becomes thermodynamically favorable through the reaction between C₃N₄ and dry ice (CO₂) at 31 GPa. P1-C₇N₄O₈ exhibits excellent structural stability under high pressure and can be retained at ambient conditions. C–N and C–O single bonds are elongated during decompression to atmospheric pressure, which can increase the energy density further. As a result, P1-C₇N₄O₈ shows outstanding mass density (3.08 g cm⁻³) and volumetric energy density (18.12 kJ cm⁻³) at ambient conditions, outperforming those of CHON and C_xN_yO_z energetic materials. This work indicates that a 3D covalent structure with uniform chemical single bonds is crucial for balancing the stability and performance of energetic materials.