K+ Ion Assisted Regeneration of Active Cyano Groups in Carbon Nitride Nanoribbons for Visible‐Light Driven Photocatalytic Nitrogen Reduction

: As a metal-free nitrogen reduction reaction (NRR) photocatalyst, g-C3 N4 is available from a scalable synthesis at low cost. Importantly, it can be readily functionalized to enhance photocatalytic activities. However, the use of g-C3 N4 -based photocatalysts for the NRR has been questioned because of the elusive mechanism and the involvement of N defects. This work reports the synthesis of a g-C3 N4 photocatalyst modified with cyano groups and intercalated K+ (mCNN), possessing extended visible-light harvesting capacity and superior photocatalytic NRR activity (NH3 yield: 3.42 mmol g-1  h-1 ). Experimental and theoretical studies suggest that the -C≡N in mCNN can be regenerated through a pathway analogous to Mars van Krevelen process with the aid of the intercalated K+ . The results confirm that the regeneration of the cyano group not only enhances photocatalytic activity and sustains the catalytic cycle, but also stabilizes the photocatalyst.