Bi₂O₂CO₃/CdS S-Scheme Heterojunction with Efficient Interfacial Charge Separation for Optimized H₂O₂ Photosynthesis from Seawater

Exploring highly efficient photocatalytic materials is of utmost importance for the efficient generation of hydrogen peroxide (H₂O₂) in seawater. However, the catalytic performance of such materials is constrained by low solar energy conversion efficiency and inadequate charge carrier separation. In this study, narrow-bandgap CdS nanoparticles with high reducibility, synthesized via a hydrothermal method, are coupled with Bi₂O₂CO₃ (BOC) nanosheets to construct S-scheme BOC/CdS heterojunctions. These heterojunctions effectively optimize charge transfer, broaden light absorption, accelerate charge separation and migration, maintain strong redox capabilities, and enable dual pathways for two-electron water oxidation and oxygen reduction. Systematic characterizations, including in situ X-ray photoelectron spectroscopy/Fourier transform infrared spectroscopy, Kelvin probe force microscopy, electron spin resonance, and femtosecond transient absorption spectroscopy, are performed to elucidate the H₂O₂ generation pathways, clarify the charge transfer and separation mechanisms, and confirm the S-scheme mechanism. The optimized BOC/CdS heterojunction demonstrates superior H₂O₂ production in seawater, reaching 1904 μmol/(g h), which is 17.96-fold that of BOC and 2.13-fold that of pure CdS. Moreover, its performance in seawater is remarkable compared to that in deionized water. Overall, this research presents a viable strategy for designing S-scheme catalysts to enhance H₂O₂ photosynthesis from seawater.