Donor–Acceptor Fully Sp2-Carbon Conjugated Covalent Organic Frameworks for Photocatalytic H2O2 Production

Abstract

Covalent organic frameworks (COFs) are promising for photocatalytic H₂O₂ generation. However, imine-linked COFs often suffer from poor charge separation and low photocatalytic performance. Therefore, constructing sp² carbon-linked COFs with extended π-conjugation is very significant in boosting the photocatalytic properties, but their synthesis is challenging due to the low reversibility of C═C bond. Here, two vinylene-linked COFs: BBT-ACN COF-1 and BBT-ACN COF-2 are designed. To investigate the effects of different structures on exciton binding energy (E_b), the designed BBT-ACN COF-1 possesses a Donor–Acceptor (D–A) structure with the electron-deficient benzobisthiazole (BBT) as acceptor and benzotrithiophene as donor, while the latter holds a π-A structure with pyrene as π-unit and BBT as acceptor. Both BBT-ACN COFs show photocatalytic H₂O₂ production activity in a two-step 2e⁻ oxygen reduction reaction (ORR).  As anticipated, the D–A structured BBT-ACN COF-1 exhibits a lower E_b value, and its photocatalytic H₂O₂ production rate in pure water and air reaches up to 2.50 mmol g⁻¹ h⁻¹, ≈3 times higher than that of the π-A structured BBT-ACN COF-2 (0.91 mmol g⁻¹ h⁻¹). This study reveals that constructing fully sp²-carbon-linked COFs is very beneficial for photocatalytic H₂O₂ production, which provides an effective approach for designing high-performance organic photocatalysts.