Electronic Modulation of K⁺‐Intercalated Polymeric Carbon Nitride via ─C≡N/─OH Functionalization for Efficient Photocatalytic H ₂ O ₂ Production

Polymeric carbon nitride (PCN) holds great promise for photocatalytic H₂O₂ production owing to its excellent stability and structural tunability. However, the inferior overall photocatalytic performance of PCN owing to its limited charge separation efficiency is a longstanding challenge. Herein, a K⁺-doped bridge-type PCN featuring ─C≡N and ─OH surface groups is synthesized via thermal polymerization. K-PCN exhibits superior efficiency for photocatalytic H₂O₂ production (8647.78 µM·h^-1) with a quantum efficiency of 17.92% at 420 nm, remarkably surpassing that of PCN (86.96 µM·h^-1 and 0.129%). K⁺ ions tend to reside within the interlayers of PCN, where they create K⁺-bridges that reduce interlayer spacing, strengthen π-π stacking, and improve crystallinity, thereby accelerating charge transport by shortening carrier migration pathways and suppressing recombination. Moreover, K⁺ perturbs the local electronic structure via interaction with nitrogen lone pairs, thereby narrowing the bandgap and enhancing visible-light absorption. The introduction of ─C≡N and ─OH groups enrich the surface with polar sites, with ─C≡N promoting O₂ adsorption and activation through electron delocalization and ─OH increasing hydrophilicity and O₂ concentration via hydrogen bonding. This study elucidates the pathway and mechanism of photocatalytic oxygen reduction and provides novel insights into the reasonable design of bridge-type group-modified PCN for efficient H₂O₂ production.