COF-based electrocatalysts for the hydrogen evolution reaction: construction strategies, performance enhancement, and challenges

The hydrogen evolution reaction (HER) is a key half-reaction in water electrolysis. Covalent organic frameworks (COFs), offer ordered pores, tunable structures, and designability. However, intrinsic conductivity, active-phase ambiguity, framework instability, and limited device-level validation hinder practical HER application. In this review, recent progress in COF-based HER electrocatalysts is critically discussed, with particular emphasis on framework construction and morphology control, active-site design and electronicstructure regulation, conductive networkdesign, heterointerface coupling, and electrode integration. Rather than simple structural classification, this review emphasizes how framework programmability translates into catalytic function. The effects of these structural design strategies on catalytic activity, charge-transfer behavior, and durability are discussed in detail. Particular attention is paid to distinctions among pristine, metalated, hybrid, and COF-derived active phases. Device-level performance in membrane and zero-gap electrolyzers is also considered. Finally, the major challenges currently facing this field are highlighted, including active-phase identification, intrinsic conductivity improvement, framework stability, scalable synthesis, and device-relevant electrode operation. This review aims to clarify the structure-function logic of COF-based HER catalysis and guide the development of mechanistically identifiable and practically relevant catalysts.