Oriented construction of crystal phase homojunction and proton relay on CdS for boosting photocatalytic hydrogen peroxide production

Photocatalytic oxygen reduction to produce hydrogen peroxide (H 2 O 2 ) represents a sustainable and environmentally friendly approach for H 2 O 2 photosynthesis, while the activity is still severely limited by the slow charge and proton dynamics. Herein, we constructed CdS-based homojunctions which composed of cubic and hexagonal phases by simply capping of CdS with 3-mercaptopropionate (MPA) for visible light-driven H 2 O 2 production. Characterization results suggested the commensalism and intimate contact of cubic and hexagonal phases in the resulted MPA-CdS photocatalysts, which improved light harvesting, and boosted the charge separation and transfer at homojunction interface. MPA capping agents on CdS surfaces also served as proton relays and localize protons near the active sites towards efficient photocatalytic O 2 reduction. Thus, the problems caused by both slow charge transfer and sluggish proton dynamics can be resolved. Furthermore, the coordination between MPA and Cd 2 + ions prevented Cd 2+ leaching into solution, which retarded the oxidative holes induced photocorrosion of CdS due to the Cd 2+ confinement effect. Consequently, the obtained MPA-CdS-x catalysts, especially, MPA-CdS-6, achieved excellent photocatalytic H 2 O 2 production rate (1250.17 µmol g⁻¹ h⁻¹) under visible light from H 2 O and O 2 without any sacrificial agents, which was 2.2 times higher than its bare CdS counterpart (580.07 µmol g⁻¹ h⁻¹). This study proposes a simple and excellent method to enhance charge and proton transfer for high-performance H 2 O 2 green production.