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

Two-dimensional (2D) carbon nitrides (CN) have great potential in advanced fields such as energy harvest and storage. We report a novel 2D CN, CN, comprising sp-N and sp-C atoms. Density functional theory calculations indicate that electronically, thermally, and dynamically stable CN is metallic even when cut into very narrow nanoribbons. CN 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 CN had excellent overall performance including promising stability, moderate binding strength of H and H, and good electrical conductivity. Our results suggest a novel CN with an sp-N skeleton that has great potential for HER. More investigations are needed to further understand the properties and applications of CN in other fields.