Enhancing the energy density of CNO compounds through distorted carbon tetrahedra

Abstract

Carbon, nitrogen, and oxygen compounds have attracted considerable interest due to their ability to store and release energy through variations in bond strength. However, identifying the stable stoichiometric ratios of CxNyOz ternary compounds remains a significant challenge. Here, we introduce the electron counting rule for the design of CxNyOz compounds, coupled with a first-principles structure search method. The results demonstrate that the discovered CxNyOz structures exhibit higher thermodynamic stability on the convex hull diagram than previously reported CxNyOz compounds at 40 GPa. Interestingly, these structures consist of distorted carbon tetrahedra and retain their structural characteristics under ambient conditions. Beyond conventional understanding, we have identified the distortion degree of carbon tetrahedra as another physical factor that can effectively enhance the energy density of CxNyOz compounds. Their energy density reaches values of 15.92–20.59 kJ/cm3, which are significantly superior to those reported previously. Our work opens an avenue for designing stable CxNyOz compounds with ultrahigh energy density.