Optimizing *OOH Binding on Enamine‑Carbon Sites in Heterostructures for Superior 2e − Oxygen Reduction

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ABSTRACT Identifying and tuning the genuine active sites in covalent organic frameworks (COFs) is crucial for steering the oxygen reduction reaction (ORR) toward the two‐electron (2e − ) pathway to hydrogen peroxide (H 2 O 2 ). Here, we report a systematic investigation of four isostructural COFs with pendant groups of diverse electronic nature (‐H, ‐SO 3 H, ‐COOH, ‐NH 2 ), grown as uniform shells on carbon nanotubes (CNTs). Mechanistic analyses pinpoint the β‑ketoenamine‑linked carbon atom as the universal active center across all functionalized frameworks. The strongly electron‑withdrawing ‐SO 3 H moiety is found to optimally polarize this site, yielding a near‑ideal *OOH adsorption free energy that maximizes the 2e − selectivity. The resulting COF‐SO 3 H@CNT heterostructure delivers an outstanding H 2 O 2 selectivity of 97.0% in 0.1 M KOH, together with a Faradaic efficiency of 89.2% and a stable production rate of 345 mmol g cat −1 h −1 at 10 mA cm −2 in an H‑cell. Operando Raman spectroscopy directly captures the potential‑dependent emergence of the *OOH intermediate on the ‐SO 3 H‑modified framework, while the electron‑donating ‐NH 2 group delays this signal and promotes the competing 4e − route. This work uncovers the role of substituent electronic effects in ORR branching and provides a blueprint for metal‐free COF electrocatalyst design through local electronic modulation of carbon active sites.

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