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 µmol 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 O₂ 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. © 2022 Wiley-VCH GmbH.