Ladder‐Like Built‐In Electric Field Enhances Self‐Assembly, Carrier Separation and Ultra‐Efficient Photocatalytic Oxygen Reduction

Semiconductor heterojunctions can significantly enhance the separation of photogenerated charge carriers, among which Z-type heterojunctions are more conducive to photocatalysis due to their special transfer paths and strong oxidizing and reducing properties. However, introducing efficient active sites has always been a significant challenge in the improvement of heterogeneous photocatalysts. Herein, through in-depth analysis of the reaction mechanism and structural characteristics, single atom catalysts and heterojunctions are ingeniously integrated using built-in electric fields. For the first time, the suitable metal single atom active sites are successfully designed under the special electronic structure at the N-terminal, utilizing low electronegativity non-metallic element doping to counteract local electron migration from heterojunctions. Ladder-like built-in electric field composed of the divergent and parallel built-in electric fields from single atom catalysts and heterojunctions respectively, which introduces a new carrier separation path. AgPCN/BCN heterojunction reaches a hydrogen peroxide (H₂O₂) yield 559.5 µM∙h^-1 and an apparent quantum efficiency of 17.8% through 2e^- oxygen reduction reaction. Photoelectrochemical tests indicate the importance of 4e^- water oxidation reaction as an auxiliary reaction. This novel and innovative photocatalyst structure brings new approaches for photocatalysts improvement, and new insights into the role of built-in electric fields in photocatalytic reaction mechanisms.