Identification of Topological Metal g-C₂N with High Activity and Selectivity for Versatile Oxygen Electrocatalysis

Two-dimensional (2D) carbon nitride materials are emerging as ideal supports for single-atom catalysts (SACs) due to their excellent physicochemical stability, abundant active sites, and ample capacity for metal loading. However, their intrinsic semiconducting properties constrain electrical conductivity, thereby hindering charge transfer during catalytic processes. Herein, we propose a graphene-like 2D carbon nitride structure, g-C₂N, derived from first-principles calculations and theoretical analysis. This structure is identified as a topological metal, featuring a symmetry-protected Dirac cone. Its topologically nontrivial nature is evidenced by distinct edge states, nonzero Berry curvature, and quantized Zak phase. Remarkably, g-C₂N exhibits a Fermi velocity exceeding that of graphene. Furthermore, the constructed Co@C₂N₂ structure is identified as a highly active and selective catalyst for hydrogen peroxide (H₂O₂) electrosynthesis, with a low thermodynamic overpotential of 0.08 V. Additionally, the Co@C₂N₂-N catalyst developed through N-doping strategies demonstrates outstanding bifunctional 4e^- OER/ORR activity with low overpotentials of 0.27 and 0.32 V, respectively. These findings not only broaden the scope of 2D carbon nitride materials but also offer foundational insights for the rational design of highly active catalysts for oxygen electrocatalysis.