Efficient overall photosynthesis of H₂O₂ by the BTz@Mn_0.2Cd_0.8S S-scheme heterojunction

The photosynthesis of hydrogen peroxide (H₂O₂) through the selective 2e⁻ oxygen reduction reaction (ORR) from O₂ and H₂O stands out as an environmentally sustainable and cost-effective method for generating this essential chemical. Unfortunately, the widespread application of most photocatalysts is impeded by their reliance on sacrificial agents. In this context, we present a noteworthy advancement in the form of a step-scheme (S-scheme) heterojunction involving a donor–acceptor (D–A)-conjugated polymer and manganese cadmium sulfide (BTz@MCS). This innovative configuration enables efficient photocatalytic H₂O₂ production within a non-sacrificial system, showcasing an impressive H₂O₂ yield of 5,368 µmol g⁻¹ h⁻¹ and an apparent quantum yield of 4.5% at 420 nm. Through insights gained from in-situ irradiated X-ray photoelectron spectroscopy (ISIXPS), in-situ diffuse reflectance infrared Fourier transformations spectroscopy (DRIFTS), and density function calculations (DFT), it is revealed that the sp² C between thiazole–thiazole rings at the BTz and the concentrated holes at the MCS function as spatially separated redox centers. These centers catalyze the selective 2e⁻ ORR and 4e⁻ water oxidation reaction (WOR) concurrently. The O₂ generated from the WOR is subsequently utilized by the ORR cycle, enabling the overall photosynthesis of H₂O₂ with accelerated total reaction kinetics. Furthermore, the high photocatalytic performance of the developed catalyst is attributed to well-designed S-scheme heterojunctions with tuned band structures. The spatially separated redox centers and effective transfer of photogenerated charge carriers facilitated by the internal electric field significantly enhance reaction kinetics. This study introduces a promising avenue for photocatalytic H₂O₂ production without sacrificial agents, providing valuable insights into the underlying mechanisms in S-scheme heterojunctions.