Hydrogen Radicals Enable an Alternative Kinetic Pathway for H₂O₂ Photosynthesis through Dual Redox Site Regulation of Proton-Coupled Electron Transfer.

Abstract

Artificial photosynthesis offers a sustainable route for hydrogen peroxide (H₂O₂) production, yet its efficiency is fundamentally limited by the kinetic decoupling of proton-coupled electron transfer (PCET) during oxygen reduction. Here, we demonstrate that hydrogen radicals (H•) enable an alternative kinetic pathway for H₂O₂ formation by accelerating the conversion of *OOH intermediates. This mechanism is realized through dual redox site regulation in Cu and O co-modified Zn₃In₂S₆ (denoted as O/Cu-ZIS). The introduction of Cu dopants increases hole density in the Zn─S layers, accelerating water oxidation kinetics and facilitating interfacial proton availability for oxygen reduction, while oxygen incorporation modulates the electronic structure of the In-S layer to promote electron transport, enhance O₂ activation, and weaken the interaction between protons and S sites. Quenching experiments and electron paramagnetic resonance spectroscopy support the participation of H• in the conversion of *OOH intermediates, providing an additional kinetic channel beyond conventional PCET. Finally, O/Cu-ZIS achieves a H₂O₂ production rate of 167.1 µmol g^-1 min^-1 from pure H₂O and O₂, markedly exceeds most state-of-the-art photocatalysts. This work establishes H• as active intermediates in photocatalytic H₂O₂ evolution and provides a strategy for regulating PCET via dual redox site design.