COF-Based S-Scheme Photocatalysts for CO2 Conversion: Interfacial Charge Migration and Molecular Activation

Solar-driven photocatalytic CO₂ conversion offers a sustainable route for coupling carbon recycling with solar-to-chemical energy storage. However, its efficiency and product selectivity are limited by rapid charge recombination, inefficient CO₂ enrichment and activation, competing proton reduction, and poorly controlled electron/proton transfer during multistep conversion. Covalent organic framework (COF)-based step-scheme (S-scheme) heterojunctions provide a distinctive platform in which selective interfacial recombination can promote charge separation while preserving strongly reducing electrons and oxidizing holes. Meanwhile, the molecular programmability of COFs enables the regulation of interfacial coupling, catalytic sites, and pore microenvironments to facilitate CO₂ enrichment and activation and control reaction pathways. This Review examines how COF-based S-scheme interfaces are constructed, how their charge-transfer pathways can be reliably established, and how interfacial charge migration translates into productive CO₂ chemistry. Particular attention is paid to interfacial bonding, charge redistribution, built-in electric-field formation, photoinduced carrier migration, and their relationships with intermediate stabilization and multielectron reduction. A central conclusion is that charge separation and catalytic charge utilization are distinct but inseparable design challenges. Future advances will require chemically well-defined interfaces, operando and time-resolved mechanistic validation, and the reaction-specific integration of charge migration, active-site chemistry, proton transfer, and pore microenvironments.