Polarization Engineering of Covalent Triazine Frameworks for Highly Efficient Photosynthesis of Hydrogen Peroxide from Molecular Oxygen and Water

Two-electron oxygen photoreduction to hydrogen peroxide (H2O2) is seriously inhibited by its sluggish charge kinetics. Herein, a polarization engineering strategy is demonstrated by grafting (thio)urea functional groups onto covalent triazine frameworks (CTFs), giving rise to significantly promoted charge separation/transport and obviously enhanced proton transfer. The thiourea-functionalized CTF (Bpt-CTF) presents a substantial improvement in the photocatalytic H2O2 production rate to 3268.1 mu mol h(-1) g(-1) with no sacrificial agents or cocatalysts that is over an order of magnitude higher than unfunctionalized CTF (Dc-CTF), and a remarkable quantum efficiency of 8.6% at 400 nm. Mechanistic studies reveal the photocatalytic performance is attributed to the prominently enhanced two-electron oxygen reduction reaction by forming endoperoxide at the triazine unit and highly concentrated holes at the thiourea site. The generated O-2 from water oxidation is subsequently consumed by the oxygen reduction reaction (ORR), thereby boosting overall reaction kinetics. The findings suggest a powerful functional-groups-mediated polarization engineering method for the development of highly efficient metal-free polymer-based photocatalysts.

Automated summary

In this study, a polarization engineering strategy was used to enhance the two-electron oxygen photoreduction to hydrogen peroxide by grafting (thio)urea functional groups onto covalent triazine frameworks. The functionalized framework showed significantly improved charge separation/transport and proton transfer, leading to a substantially higher production rate of hydrogen peroxide compared to the unfunctionalized framework. This approach provides a new direction for the development of efficient metal-free polymer-based photocatalysts.