Effect of Carbon Doping on CO₂‐Reduction Activity of Single Cobalt Sites in Graphitic Carbon Nitride

Abstract Single‐atom catalysts have demonstrated interesting activity in a variety of applications. In this study, we prepared single Co²⁺ sites on graphitic carbon nitride (C₃N₄), which was doped with carbon for enhanced activity in visible‐light CO₂ reduction. The synthesized materials were characterized with a variety of techniques, including microscopy, X‐ray powder diffraction, UV‐vis spectroscopy, infrared spectroscopy, photoluminescence spectroscopy, and X‐ray absorption spectroscopy. Doping C₃N₄ with carbon was found to have profound effect on the photocatalytic activity of the single Co²⁺ sites. At relatively low levels, carbon doping enhanced the photoresponse of C₃N₄ in the visible region and improved charge separation upon photoactivation, thereby enhancing the photocatalytic activity. High levels of carbon doping were found to be detrimental to the photocatalytic activity of the single Co²⁺ sites by altering the structure of C₃N₄ and generating defect sites responsible for charge recombination.