Photocatalysis offers a promising route for using light to produce clean fuels and valuable chemicals. Hydrogen is widely viewed as a clean energy carrier, while hydrogen peroxide is an important green oxidant used in chemical manufacturing, environmental remediation, and disinfection. In a study published in Research, researchers from Chongqing Technology and Business University, Sichuan University, and Southwest Medical University report a Bi₂WO₆/Zn-TCPP (BWO/ZTP) inorganic–organic S-scheme heterojunction that improves photocatalytic production of both H₂ and H₂O₂ by strengthening interfacial charge separation.

A major limitation in photocatalysis is the rapid recombination of photogenerated electron-hole pairs. When these charge carriers recombine before participating in surface reactions, catalytic efficiency drops. S-scheme heterojunctions are designed to address this challenge by preserving highly reducing electrons and strongly oxidizing holes while eliminating less useful charge carriers. In principle, this allows a photocatalyst to combine efficient charge separation with strong redox capability.

The research team constructed a two-dimensional inorganic–organic heterojunction using bismuth tungstate as the inorganic component and zinc porphyrin nanosheets as the organic semiconductor. Through an interface-induced growth strategy, Zn-TCPP was grown in situ on the surface of BWO, forming a compact 2D/2D BWO/ZTP interface rather than a simple physical mixture. This close contact is important because it provides a pathway for rapid interfacial charge transfer and supports the formation of a strong built-in electric field.

The optimized material, BWO/ZTP-1, showed markedly improved photocatalytic activity. Under visible-light irradiation, it achieved a hydrogen evolution rate of 2,343.3 μmol·g^-1·h^-1, 14.9 times higher than pristine BWO and 3.44 times higher than Zn-TCPP. It also produced hydrogen peroxide at 236.1 μmol·g^-1·h^-1, representing 2.33-fold and 2.27-fold improvements over the two individual components. The catalyst maintained its activity over repeated cycles, suggesting favorable structural and catalytic stability under the tested conditions.

Mechanistic studies showed that the built-in electric field plays a central role. Because BWO and Zn-TCPP have different Fermi levels, contact between the two materials induces interfacial charge redistribution. This produces an internal electric field that drives photogenerated electrons and holes in opposite directions under illumination. As a result, charge recombination is suppressed, while the electrons and holes retained in the system preserve strong reduction and oxidation ability. Femtosecond transient absorption spectroscopy revealed a much longer charge lifetime in BWO/ZTP-1, while Kelvin probe force microscopy, in situ X-ray photoelectron spectroscopy, and density functional theory supported directional charge transfer at the interface.

The study also examined the hydrogen peroxide production pathway. Experimental evidence indicated that H2O2 is mainly generated through a two-step one-electron oxygen reduction route, in which oxygen is first converted into superoxide radicals and then further reduced to hydrogen peroxide. Radical detection experiments showed that BWO/ZTP-1 generates stronger reactive oxygen signals than the individual components, consistent with enhanced redox activity on both sides of the heterojunction.

The significance of this work lies in its interface-focused design strategy. Rather than merely combining two photocatalysts, the study demonstrates how a tightly coupled inorganic–organic S-scheme heterojunction can use a built-in electric field to coordinate light absorption, charge separation, and surface redox reactions. Before practical deployment, further work will be needed to evaluate performance under more realistic solar conditions, reduce dependence on sacrificial agents, improve scalability, and test long-term durability. Still, the BWO/ZTP system provides a useful design reference for developing next-generation photocatalysts for solar fuel and green chemical production.

The complete study is accessible via DOI:10.34133/research.1166