Synergistic effect of Ru-N₄ sites and Cu-N₃ sites in carbon nitride for highly selective photocatalytic reduction of CO₂ to methane

Developing single-atom photocatalysts for selective conversion of CO₂ to valuable fuel is of great attraction but remains challenging. In this work, ruthenium and copper single atoms are for the first time simultaneously incorporated into polymeric carbon nitride (PCN) through a simple preassembly-coprecipitation-pyrolysis process. The obtained PCN-RuCu sample exhibited much higher selectivity (95%) for CH₄ production than the individual Ru or Cu decorated PCN during photocatalytic CO₂ reduction under visible-light irradiation. The atomically dispersed Ru-N₄ and Cu-N₃ moieties were confirmed by spherical aberration-corrected electron microscopy and extended X-ray absorption fine structure spectroscopy. Density function theory (DFT) calculations revealed that the co-existence of Ru-N₄ sites and Cu-N₃ sites can effectively tune the electronic structure of PCN, making the Ru sites account for photogenerated electron-hole pairs and the Cu sites for CO₂ hydrogenation. Moreover, the synergetic effect between Ru and Cu single atoms significantly promotes the consecutive hydrogenation processes of *CO species towards CH₄ production. Our studies provide a new understanding of the mechanism for photocatalytic reduction of CO₂ to CH₄, and pave a new way to design photocatalysts for the selective production of solar fuels.