Elucidating Unique Synergic Enhancement Effect for H₂O₂ Production in Crystalline Carbon Nitride with Cyanamide‐Defect and Heptazine‐Triazine Junction

Abstract Cyanamide‐defect and heptazine/triazine (H/T) junction in g‐C₃N₄ (CN) have commonly been considered as an effective strategy for solar‐driven artificial H₂O₂ photosynthesis. However, their synergistic effect is still ambiguous regarding how to manipulate free electrons to effectively participate in the O₂ reduction to H₂O₂. Herein, through the alkali‐salt‐assist‐thermal polymerization approach, a series of g‐C₃N₄ samples with cyanamide‐defect, and H/T junction aredeveloped. Subsequently, it is demonstrated that the appropriate ratio of cyanamide defect and H/T junction in crystalline CN can respectively facilitate the formation of free electrons at the shorter and longer lifetime scales due to their different strength driving forces. These electrons at the different lifetime scales can synergically and effectively participate in the direct 2e⁻ and stepwise radical process for efficient H₂O₂ production. Eventually, it can elucidate that the optimal photocatalyst, owing to its crystalline structure with the proper ratio of H/T junction and cyanamide defect, achieved a remarkable H₂O₂ yield of 60.03 mmol h⁻¹ g⁻¹ with a quantum efficiency of 43.7% at 420 nm and a solar‐to‐chemical‐conversion efficiency of 2.55% under AM 1.5G irradiation. This work will open a bright avenue for the design of organic photocatalysts to manipulate charge carriers effectively engaging in the surface reaction.