Na ⁺ /K ⁺ -Intercalation Crystalline Carbon Nitride with High Charge Transfer Efficiency For Synergistically Enhanced Photocatalytic H ₂ O ₂ Production

g-C₃N₄-based photocatalysts have attracted considerable research attention for their applicability in green H₂O₂ production. However, the photocatalytic activity of these catalysts is limited by their low light-absorption efficiency and high carrier recombination rate. This study developed a highly crystalline carbon nitride (CDCN-<i>X</i>) through thermal polymerization using eutectic salt, which promoted the incorporation of cyano groups, created electron-transport "bridges", and guided directional material growth into a nanorod morphology. Enhanced crystallinity effectively minimized internal defects within the material, thus notably suppressing the recombination of photogenerated electron-hole pairs. Cyano groups and Na⁺/K⁺ ions were introduced to modulate the electronic band structure of CDCN-X and establish an internal built-in electric field, thus achieving a broader light absorption range and efficient transport channels for photogenerated charge carriers. Additionally, the cyano groups served as active sites, enhancing the adsorption capacity for O₂ and promoting the reaction progress. As a result of these modifications, CDCN-550 enabled rapid two-step single electron oxygen reduction, thereby promoting rapid H₂O₂ generation. Furthermore, a CDCN-550-catalyzed H₂O₂ yield of 36.69 mmol g^-1 h^-1 was achieved, representing a 17.39-fold increase compared to conventional carbon nitride (DCN). Overall, the proposed approach is viable for the rational design and modification of carbon nitride materials to achieve excellent photocatalytic performance.