Boosting Photocatalytic H ₂ Evolution With Crystalline g‐C ₃ N ₄ From a Fixed‐Temperature Intermediate‐Stage Polymerization

Graphitic carbon nitride (g‐C ₃ N ₄ ) holds great promise for photocatalytic hydrogen evolution, yet its efficiency is often limited by structural imperfections. Herein, we report a synthesis strategy that systematically engineers the polymerization process by controlling the intermediate‐stage temperature and precursor (dicyandiamide, DCY) mass. The optimized sample (CCN‐3.5), prepared at 240°C with 3.5 g of DCY, exhibits enhanced crystallinity and a remarkable hydrogen‐evolution rate of 4355 μmol h ⁻¹ g ⁻¹ , which is 5.71 times that of the pristine polymer. This superior performance is attributed to the optimized structure that facilitates charge migration. In contrast, excess precursor was found to disrupt structural integrity and impair photocatalytic activity. This work highlights the critical role of polymerization control in developing high‐performance g‐C ₃ N ₄ photocatalysts.