Coupling Water Oxidation and Oxygen Reduction for Photocatalytic H₂O₂ Production over ZnIn₂S₄/UiO66-NH₂ Heterojunctions via Dual Channel Pathways

Artificial photosynthesis of hydrogen peroxide (H₂O₂) from oxygen and water is a promising approach for converting low-density solar energy into versatile chemical energy. However, the generation of H₂O₂ through a single-channel oxygen reduction reaction (ORR) is prevalent, while the water oxidation reaction (WOR) is frequently neglected. Herein, we constructed Z-scheme ZnIn₂S₄/UiO66-NH₂ (ZIS/UNH) heterojunctions, integrating the ORR and WOR dual pathways for photocatalytic H₂O₂ generation without noble cocatalysts and sacrificial agents. The optimized ZIS/UNH exhibits the highest H₂O₂ yield of 0.85 mmol g^-1 h^-1, which is 2.2 and 14 times those of ZIS and UNH, respectively. The formation of the Z-scheme heterojunction efficiently promotes the separation and transfer of photogenerated carriers while retaining holes with high oxidizing ability and electrons with strong reducing ability. The free radical quenching and DMPO-ESR radical trapping experiments demonstrate that the ZIS/UNH heterojunctions produce H₂O₂ in a dual-channel mode different from the single-channel ZIS. The pathways for H₂O₂ generated by ZIS/UNH consist of a two-step single-electron ORR with ·O₂^- as an intermediate product and a direct one-step WOR.