The atomic structures of carbon nitride sheets for cathode oxygen reduction catalysis

Carbon nitride sheets are promising Pt replacement materials for cathode oxygen reduction catalysis. Using first principles calculations with a global optimization method, we search for the most stable structures of the monolayer carbon nitrides at various C:N ratios. The results show that the larger the ratio, the more energetically favorable the obtained structures, and the more preferably for the C, N atoms to assume sp² configurations. A volcano shape is revealed for the curve of the representative O₂ adsorption energies on the sheets vs. the ratios. In the ratio range of 2.0–3.0, the sheets not only have lower formation energies than the stable graphitic-C₃N₄, but also can potentially catalyze the oxygen reduction as efficiently as Pt.