Iron oxide-promoted photochemical oxygen reduction to hydrogen peroxide (H2O2)†

Hydrogen peroxide (H₂O₂) is a valuable green oxidant with a wide range of applications. Furthermore, it is recognized as a possible future energy carrier achieving safe operation, storage and transportation. The photochemical production of H₂O₂ serves as a promising alternative to the waste- and energy-intensive anthraquinone process. Following the 12 principles of Green Chemistry, we demonstrate a facile and general approach to sustainable catalyst development utilizing earth-abundant iron and biobased sources only. We developed several iron oxide (FeO_x) nanoparticles (NPs) for successful photochemical oxygen reduction to H₂O₂ under visible light illumination (445 nm). Achieving a selectivity for H₂O₂ of >99%, the catalyst material could be recycled for up to four consecutive rounds. An apparent quantum yield (AQY) of 0.11% was achieved for the photochemical oxygen reduction to H₂O₂ with visible light (445 nm) at ambient temperatures and pressures (9.4–14.8 mmol g⁻¹ L⁻¹). Reaching productivities of H₂O₂ of at least 1.7 ± 0.3 mmol g⁻¹ L⁻¹ h⁻¹, production of H₂O₂ was further possible via sunlight irradiation and in seawater. Finally, a detailed mechanism has been proposed on the basis of experimental investigation of the catalyst's properties and computational results.