Carboxyl‐Functionalized Condensed Poly (Heptazine Imide) for Synergistically Enhanced Photocatalytic Hydrogen Evolution

Despite poly (heptazine imide) (PHI) being able to reduce the undesirable structural defects in conventional polymerized amorphous carbon nitride, achieving precise control of ideal defects and high photocatalytic hydrogen yields remains a challenge. Herein, we incorporated a controlled intrinsic COOH groups with well‐defined density and location into the highly condensed PHI framework. The density of the COOH groups can be precisely regulated by simply adjusting the mass ratio of the precursors KSCN to polymeric carbon nitride. Further investigations indicate that these COOH groups enable the p‐orbital electrons of O atoms to couple with the vacant d‐orbitals of Pt, facilitating spatial separation of trapped electrons at COOH from the crystalline bulk. Moreover, a correlation between accurate COOH density with H 2 O adsorption was established, attributed to varying hydrogen bonds. As a result, these synergistic factors drive the photocatalytic water splitting process within PHI‐COOH, resulting in a remarkable H 2 evolution rate of up to 1040.3 μmol h −1 , which is approximately 129 times higher than that of the pristine PHI.