Thermodynamic and Kinetic Modulation of Artificial H₂O₂ Photosynthesis via Spatial Control of Redox Catalytic Sites

The thermodynamic and kinetic mismatch between oxidative and reductive half-reactions represents a central barrier in photocatalysis, largely due to the absence of well-defined and functionally differentiated active sites. Herein, we construct Co and Pt redox dual-site catalysts (CoPt RDSCs), featuring nonbonded yet spatially close single atoms anchored on carbon nitride for H₂O₂ photosynthesis, thereby enabling site-specific utilization of photogenerated holes and electrons. The Co sites act as the hole centers that drive the four-electron water oxidation reaction, whereas the Pt sites serve as the electron centers that catalyze the two-electron oxygen reduction reaction, each lowering the thermodynamic barrier of its respective half-reaction. Crucially, the proximity of these electronically decoupled sites enables the directed migration of the oxidation products (O₂ and H⁺) generated at Co sites to neighboring Pt sites, establishing an internal redox-coupling pathway that accelerates the overall reaction kinetics. Multidimensional in situ spectroscopy, transient photodynamics, and theoretical analyses confirm that each half-reaction proceeds on the designated site independently yet synergistically. Consequently, the CoPt RDSCs achieve a 19.33% apparent quantum efficiency at 420 nm and a 1.46% solar-to-chemical conversion efficiency for H₂O₂ synthesis in pure water, outperforming most of the reported photocatalysts under comparable conditions. Spatial engineering of redox active sites establishes a general design principle for constructing high-performance photocatalysts capable of coordinating oxidative and reductive transformations.