Multi-Energy-State Covalent Organic Framework/Sulfur-Vacancy-Engineered Mn_0.2Cd_0.8S S-Scheme Photocatalyst for Enhanced Light Harvesting and H₂O₂ Generation.

Abstract

Hydrogen peroxide (H₂O₂) is an essential green oxidant with broad industrial relevance. Photocatalytic oxygen reduction reaction (ORR) offers a sustainable method for producing oxygen, yet its efficiency is limited by poor charge separation and severe carrier recombination. Single-component photocatalysts suffer from sluggish carrier dynamics, while multi-energy-state systems frequently experience recombination at intermediate states. S-scheme heterojunction engineering offers an effective strategy to address these challenges by regulating interfacial charge transfer while preserving strong redox potentials. Here, we report the construction of an S-scheme photocatalyst by integrating a triazine-based covalent organic framework (COF) with sulfur-vacancy-rich Mn_0.2Cd_0.8S (Sv-MCS). This dual-functional design preserves both the intrinsic n→π* electronic transitions of the COF and defect-state absorption of Sv-MCS, delivering an exceptional H₂O₂ production rate of 5389.6 µmol·h^-1·g^-1 in pure water. Concurrently, the photostability of the catalyst is simultaneously enhanced. X-ray absorption fine-structural analysis confirms interfacial Cd-O coordination between Cd atoms and COF carbonyl groups. In situ spectroscopies combined with density functional theory elucidate a preferential two-electron ORR pathway, while femtosecond transient absorption spectroscopy confirms suppressed carrier recombination enabled by synergistic S-scheme charge transfer and interfacial chemical bonding. This work establishes design principles for multi-energy-state S-scheme photocatalysts and advances solar-driven H₂O₂ production toward artificial photosynthesis.