Activating Inert Carbon Atoms in Poly(Heptazine Imide) via Doping Engineering for High‐Efficiency Photocatalytic Water Oxidation

Abstract Photocatalytic water oxidation half‐reaction is a critical bottleneck in achieving efficient overall water splitting using polymeric photocatalysts, primarily due to the lack of efficient water oxidation sites and sluggish reaction kinetics. To address these challenges, a doping engineering strategy is proposed to activate inert carbon atoms as efficient water oxidation sites in poly(heptazine imide) (PHI). Computational analysis revealed that Rb ⁺ dopants can induce in‐plane structural distortions in PHI, thereby modulating the electronic structure of carbon atoms. This modulation enhanced the adsorption of *OH intermediates on carbon atoms and significantly reduced the reaction barrier for water oxidation. Furthermore, charge carriers dynamics uncovered that the incorporation of the Rb ⁺ ions into the PHI framework can promote the photoexcited exciton dissociation and induce the holes to migrate to the water oxidation sites. As a result, the Rb‐doped PHI achieved an excellent apparent quantum efficiency value of up to 20.4% at 400 nm for water oxidation. This finding offers a new channel for researchers to develop highly efficient polymeric photocatalysts for photocatalytic water oxidation reactions.