Covalent Organic Frameworks for Photocatalytic Hydrogen Evolution: Design, Strategy, and Structure-to-Performance Relationship.

Photocatalysts are essential in photoenergy transduction systems, and their promising use for photocatalytic hydrogen evolution from water has been intensively studied for decades. Covalent organic frameworks (COFs) are emerging crystalline materials that are featured with highly ordered skeletons with intrinsic uniform pores, conferring a predesignable platform for exploring novel photocatalysts. In this review, the rapid progress of two-dimensional (2D) COFs on visible photocatalytic H 2 production from water is delineated. This review summarizes the design principles of building blocks, linkages, and reactions for constructing photocatalytic active 2D COFs with desirable electronic properties. This review introduces different strategies for enhancing photocatalytic performances by extending π-conjugation, establishing donor-acceptor (D-A) configuration, functionalizing layered structures, and incorporating heteroatoms, or metal complexes. This review details the unique synergy between 2D COFs and various functional materials, such as inorganic-organic semiconductors, emphasizing on the structure-to-performance relationship. This review further concludes with the current challenges and promising opportunities for developing COF-based photocatalysts.