Local Polarization Strategy for Efficient Sacrificial-free Hydrogen Peroxide Photoproduction

Abstract

Photocatalytic production of hydrogen peroxide (H2O2) from water and oxygen under sunlight offers a safe and sustainable alternative to traditional processes. However, the sluggish water oxidation reaction (WOR) often imposes kinetic limitations on the accompanying oxygen reduction reaction (ORR) in pure water systems. This research developed a series of tailored covalent organic frameworks (COFs) with localized polarization features to boost the reaction rates of WOR. By incorporating varying numbers of sp2-hybridized nitrogen atoms into a single benzene ring, a locally polarized electronic environment was established. In particular, the dual sp2-hybridized nitrogen atoms in pyrimidine units induce strong local polarization, which facilitates charge separation and activates adjacent C=C bonds as more favorable site for WOR. Together with the highly efficient ORR activity enabled by the two nitrogen atoms, the pyrimidine-functionalized TpDa demonstrates outstanding performance in a sacrificial-agent-free system, achieving an H2O2 production rate of 6.94 mmol g-1 h-1 and an apparent quantum yield (AQY) of 25.2%. This work establishes local polarization engineering as an effective strategy for optimizing COFs photocatalysts and highlights its potential for solar-driven chemical transformations.