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 (HO) yield 559.5 µM∙h 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.