Surface indium vacancies promote photocatalytic H₂O₂ production over In₂S₃

Photocatalytic oxygen reduction reaction (ORR) represents a green and cost-effective means to produce the high-value industrial compound H₂O₂. However, the efficient H₂O₂ synthesis awaits in-depth knowledge of the ORR mechanisms for the design of highly active photocatalysts. In this work, surface indium vacancies (denote hereafter as V_In) have been introduced into In₂S₃, which significantly boosts the photocatalytic activity for H₂O₂ production, with an optimal H₂O₂ generation rate of 4.77 ± 0.05 mmol·h^-1·g_cat.^-1 under visible light illumination (λ ≥ 420 nm) and an apparent quantum efficiency (AQE) of 7.49 ± 0.01% at 420 ± 20 nm. Mechanistic analysis reveals the multifunctionality of V_In, such as enlarging the chemisorption capacity of O₂, enriching photo-generated electrons for ORR, endorsing high reducing power to photo-generated electrons, and promoting H₂O₂ desorption. These findings justify that surface cation vacancies open up new possibilities for H₂O₂ photosynthesis by leveraging their reaction dimensions in ORR.