Deciphering the structure-function nexus of metal-integrated covalent organic frameworks for solar H₂ production

Covalent organic frameworks (COFs) are increasingly recognized as promising crystalline platforms for solar-driven H₂ evolution because of their unique architectures, extended conjugation characteristics, adjustable pore environments, and structural regularity. Nevertheless, unmodified frameworks generally exhibit inadequate photocatalytic functionality and rapid recombination of photoinduced charge carriers, limiting their performance during H₂ evolution processes. To address these limitations, extensive investigations have explored the incorporation of metallic entities into COF networks to improve light absorption, carrier mobility, interfacial redox behavior, and surface catalytic dynamics. Despite rapid developments in this area, an integrated understanding linking metallic incorporation approaches with H₂ evolution activity remains insufficient. This review therefore provides a comprehensive overview connecting the structural characteristics and catalytic functions of metal-containing COF systems for photocatalytic H₂ evolution. The fundamental chemistry and framework features of COFs are first introduced, followed by representative methodologies for incorporating metallic species and their corresponding functional effects in regulating light absorption, charge separation, proton reduction, and H₂ evolution kinetics. Finally, future research directions toward constructing highly efficient and durable COF-based photocatalysts for sustainable H₂ evolution are critically highlighted.