Alkaline-adaptive covalent organic framework photocatalysts: synergistic molecular orbital and hydrogen-bond network engineering for H2O2 production

Abstract

Alkaline hydrogen peroxide (H₂O₂) is highly desirable for critical applications due to its superior stability and reactivity, but it is incompatible with conventional near-neutral production methods. While covalent organic frameworks (COFs) show promise for photocatalytic H₂O₂ generation, their alkaline performance is severely limited by poor charge dynamics and inadequate hydrophilicity, hindering the essential 2e⁻ oxygen reduction reaction (ORR: O₂ + 2e⁻ + H₂O → HO₂⁻ + OH⁻) and 4e⁻ water oxidation reaction (WOR: 4OH⁻ → O₂ + 2H₂O + 4e⁻). This work pioneers a dual-engineering strategy (molecular orbital and interfacial hydrogen-bonding network engineering) within β-ketoenamine-linked COFs to overcome these challenges simultaneously. By contrasting phenazine-based (TP-PZ-COF) and anthracene-based (TP-AN-COF) COFs, we demonstrate that strategic integration of sp²-N heteroatoms modulates molecular orbitals and enhances n → π* transitions, optimizing charge separation and transport for efficient 2e⁻ ORR and 4e⁻ WOR. Concurrently, the planar phenazine units form robust hydrogen-bonding networks that dramatically boost hydroxide ion (OH⁻) affinity and interfacial enrichment, thereby accelerating the 4e⁻ WOR kinetics. This integrated approach enabled TP-PZ-COF to achieve an exceptional alkaline H₂O₂ production rate of 4961 µmol g⁻¹ h⁻¹ in 0.01 M NaOH, representing an 8.1-fold increase over TP-AN-COF (606 µmol g⁻¹ h⁻¹). The generated H₂O₂ efficiently degraded industrial dye pollutants. Direct experimental and theoretical validations confirmed the cooperative mechanism between charge dynamics optimization and OH⁻ affinity enhancement, providing a new blueprint for designing on-demand alkaline H₂O₂ photocatalysts.