Coupling Water Oxidation and Oxygen Reduction for Photocatalytic H 2 O 2 Production over ZnIn 2 S 4 /UiO66-NH 2 Heterojunctions via Dual Channel Pathways

Artificial photosynthesis of hydrogen peroxide (H 2 O 2 ) from oxygen and water is a promising approach for converting low-density solar energy into versatile chemical energy. However, the generation of H 2 O 2 through a single-channel oxygen reduction reaction (ORR) is prevalent, while the water oxidation reaction (WOR) is frequently neglected. Herein, we constructed Z-scheme ZnIn 2 S 4 /UiO66-NH 2 (ZIS/UNH) heterojunctions, integrating the ORR and WOR dual pathways for photocatalytic H 2 O 2 generation without noble cocatalysts and sacrificial agents. The optimized ZIS/UNH exhibits the highest H 2 O 2 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 H 2 O 2 in a dual-channel mode different from the single-channel ZIS. The pathways for H 2 O 2 generated by ZIS/UNH consist of a two-step single-electron ORR with ·O 2 – as an intermediate product and a direct one-step WOR.