Hydrogen Radicals Enable an Alternative Kinetic Pathway for H 2 O 2 Photosynthesis through Dual Redox Site Regulation of Proton‐Coupled Electron Transfer

ABSTRACT Artificial photosynthesis offers a sustainable route for hydrogen peroxide (H 2 O 2 ) 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 H 2 O 2 formation by accelerating the conversion of *OOH intermediates. This mechanism is realized through dual redox site regulation in Cu and O co‐modified Zn 3 In 2 S 6 (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 O 2 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 H 2 O 2 production rate of 167.1 µmol g −1 min −1 from pure H 2 O and O 2 , markedly exceeds most state‐of‐the‐art photocatalysts. This work establishes H• as active intermediates in photocatalytic H 2 O 2 evolution and provides a strategy for regulating PCET via dual redox site design.