Abstract: Proton-coupled electron transfer (PCET) is essential for driving the two-electron oxygen reduction pathway toward H₂O₂ production. However, the coupled integration of the adjacent water oxidation reaction and oxygen reduction reaction sites to amplify PCET presents a considerable challenge in the photocatalytic H₂O₂ production. Addressing this challenge requires overcoming the inevitable carrier recombination problem at spatially adjacent redox sites. In this work, we incorporated Co and sulfur vacancies into ZnIn₂S₄ as a photocatalyst, in which the incorporation of Co induced spin polarization, significantly inhibiting the recombination of charge carriers. While the sulfur vacancies created an unsaturated coordination environment at the metal sites to promote the adsorption of reactants, forming the spatially adjacent redox sites. Extended X-ray absorption fine structure results and density functional theory simulations revealed the formation of Co-Vs dual sites. In-situ Fourier transform infrared and Raman spectroscopy confirmed the promoted PCET. This resulted in a 3.6-fold increase (215.4 μmol g^-1 h^-1) in H₂O₂ yield compared to pure ZIS (59.6 μmol g^-1 h^-1). This work exhibited a strategy for constructing spatially synergistic sites and manipulating the electronic spin polarization, providing an effective approach to enhance photocatalytic H₂O₂ production.

Key words: Spin polarization, Proton-coupled electron transfer, Spatially adjacent redox sites, ZnIn₂S₄, Photocatalytic H₂O₂ production