Sub‐Stoichiometric [6+6] Covalent Organic Frameworks for H 2 O 2 Photogeneration in Air and Pure Water

Abstract H 2 O 2 production via photocatalytic processes using only air and water represents a sustainable avenue. However, designing photocatalysts with both high efficiency and clear structure‐activity relationships remains a significant challenge. Herein, this study reports the first successful synthesis of novel sub‐stoichiometric [6 + 6] 2D covalent organic frameworks (COFs) and their COF@COF step‐scheme (S‐scheme) heterojunctions (THT‐COF, THB‐COF, HHT‐COF, and THT‐COF@THB‐COF), all featuring kgd topology constructed from hexatopic precursors. This study demonstrates that through the dual regulation of the conjugation and linkage orientation, three sub‐stoichiometric COFs exhibit distinct charge separation efficiencies and H 2 O 2 photogeneration capabilities, with HHT‐COF displaying the best H 2 O 2 evolution rate of 4996 µmol g −1 h −1 utilizing only air and pure water. Combined experimental and theoretical studies reveal THT‐COF, THB‐COF, and HHT‐COF promote 2e − oxygen reduction and water oxidation pathways for H 2 O 2 production, with HHT‐COF presenting the lowest energy barriers in the rate‐determining step for * OOH and * OH formation. Furthermore, THT‐COF@THB‐COF‐(1:1) S‐scheme heterojunction yields an enlarged H 2 O 2 evolution rate of 4226 µmol g −1 h −1 , surpassing THT‐COF, THB‐COF, and their physical mixture by factors of 1.7, 3.5, and 3.0, respectively. This study expands the repertoire of sub‐stoichiometric COFs and provides a strong impetus for the development of efficient sub‐stoichiometric COF‐based photocatalysts.