Abstract: Photosynthesis of hydrogen peroxide (H₂O₂) from H₂O and O₂ is considered to be a promising approach. However, limited to the rapid recombination of photo-generated carriers and sluggish kinetics of O₂ reduction to H₂O₂, it is a challenge for polymeric photocatalysts to achieve efficient photocatalytic H₂O₂ production. Herein, Ag single atoms and nitrogen defects decorated carbon nitride (Ag@MCT) are constructed through self-assembly and pyrolysis methods. The optimized photocatalyst displays exceptional performance in pure water, with an H₂O₂ production rate of as high as 528.4 μmol g^-1 h^-1 and an apparent quantum yield for H₂O₂ production of 4.5 % at 420 nm. Experimental and theoretical results reveal that the Ag atomic sites act as electron mediators that promote the capture and transfer of photo-generated charge carriers, while nitrogen defects as electron collectors and reaction sites to enhance the adsorption and activation of O₂, accelerating reduction kinetics from O₂ to H₂O₂. This work presents a reliable strategy to design excellent photocatalysts by rationally modulating electronic structures and active sites for accelerating photo-generated charge carriers transfer and surface reaction kinetics.

Key words: Nitrogen defect, Single atom catalyst, Electron density, Oxygen adsorption, Hydrogen peroxide