Nitrogen‐Shift‐Engineered Pt Single‐Atom/Cluster Synergy Boosts Covalent Organic Frameworks for Photocatalytic Hydrogen Evolution

Achieving atomic-level precision in anchoring metal catalysts onto optimal support sites remains challenging due to surface heterogeneity, and the impact of local coordination on dispersion and photocatalysis is unclear. We address this by designing four isomeric COFs (imine/alkene-linked pairs) with identical topologies but distinct N-anchoring sites within hexagonal channels. For photocatalytic hydrogen evolution (PHE), Pt anchored on imine-linked COFs exhibit superior activity compared to those on alkene-based COF. The optimal PHE rate of COF-I2-Pt reaches 26.72 mmol h^-1 g^-1 which is 6.1-fold higher than alkene-linked counterpart. The apparent quantum efficiency of COF-I2-Pt reaches 12.1% at 420 nm, representing one of the best performances reported among COF-based photocatalysts. Multimodal characterization confirms imine COFs stabilize dual-active sites (Pt²⁺ species and metallic clusters), whereas alkene COFs predominantly host Pt single atoms. The imine system's superior activity arises from synergistic inter-site charge transfer between Pt clusters and isolated atoms, optimizing proton adsorption and reduction kinetics. Density functional theory calculations reveal the Pt adsorption energy on distinct nitrogen anchoring sites, the excited electron dispersion situation, and the underlying PHE mechanism. This work establishes constitutional isomerism as a platform to decouple anchoring site geometry from chemical composition, providing design principles for atomically precise photocatalyst supports.