Substoichiometric [4+3] Strategy for Constructing Subvalent COFs with Acrylonitrile Unit Toward Solar‐Driven H ₂ O ₂ Production from Seawater

ABSTRACT

Rapid charge carrier recombination and limited active site availability remain major challenges for photocatalytic production of H ₂ O ₂ in water, particularly in seawater. Herein, we propose a substoichiometric [4+3] strategy to construct a subvalent covalent organic framework (TAQ‐COF) functionalized with acrylonitrile and benzoxadiazole moieties and the off‐stoichiometry of the polymerization reaction preserves two unreacted aldehyde groups per node. The resulting TAQ‐COF exhibits outstanding visible‐light‐driven H ₂ O ₂ production in pure water without any sacrificial agent, retains approximately 93% of its activity in seawater, and demonstrates excellent recyclability and antibacterial performance. Both theoretical and experimental evidence demonstrate that the enhanced local electron density surrounding the benzoxadiazole moieties in TAQ‐COF creates a favorable microenvironment for the proton‐coupled reduction of O ₂ . Owing to its strong electron‐withdrawing effect and conjugated structure, the acrylonitrile unit markedly extends the lifetime of photogenerated charge carriers from 1.50 to 17.94 ns. Moreover, the enhanced surface hydrophilicity of TAQ‐COF sample promotes interfacial water enrichment, thereby favoring the proton‐coupled oxygen reduction reaction (ORR). The synergy of these features endows TAQ‐COF with outstanding catalytic activity in the two‐electron ORR pathway. This work demonstrates that synergistic functionalization with acrylonitrile units in a substoichiometric COF yields robust photocatalysts.