Engineering molecular-semiconductor interfaces via vacancy-triggered π–d coupling for H₂O₂ photosynthesis

Photocatalytic H₂O₂ production is limited by slow interfacial charge transfer and poorly controlled adsorption of oxygen intermediates, which reduce the selectivity of the two-electron oxygen reduction reaction. We prepared an oxygen-vacancy-rich In-TCPP@W₁₈O₄₉ heterointerface to investigate the role of π–d orbital coupling in oxygen reduction. Experiments and calculations show that oxygen vacancies enhance hybridization between the π states of In-TCPP and the W 5d states of W₁₈O₄₉. This interaction promotes interfacial charge redistribution and modifies the local electronic structure of surface W sites. The resulting electronic changes facilitate interfacial electron transfer and regulate the adsorption energies of *O₂ and *OOH intermediates, favoring a selective two-electron pathway for H₂O₂ formation. The optimized In-TCPP@W₁₈O₄₉ produces H₂O₂ at 1045 μmol g^-1 h^-1 in pure water under ambient air, 10.7 times higher than W₁₈O₄₉, with a solar-to-chemical conversion efficiency of 1.66 %. These findings indicate how oxygen-vacancy-enhanced π–d coupling may influence oxygen reduction and provide insights into designing selective solar-driven oxygen reduction photocatalysts.