C₆N₃: A novel 2D carbon nitride with sp-N as support for efficient hydrogen production

Two-dimensional (2D) carbon nitrides (C_xN_y) have great potential in advanced fields such as energy harvest and storage. We report a novel 2D C_xN_y, C₆N₃, comprising sp-N and sp²-C atoms. Density functional theory calculations indicate that electronically, thermally, and dynamically stable C₆N₃ is metallic even when cut into very narrow nanoribbons. C₆N₃ adsorbed single atoms of 3d, 4d, and 5d transition metals to fabricate single-atom catalysts (SACs) for an electrocatalytic hydrogen evolution reaction (HER). Among all SACs studied, Ti-, Cr-, Zr-, and Hf-embedded C₆N₃ had excellent overall performance including promising stability, moderate binding strength of H and H₂, and good electrical conductivity. Our results suggest a novel C₆N₃ with an sp-N skeleton that has great potential for HER. More investigations are needed to further understand the properties and applications of C₆N₃ in other fields.