Regulating spatial separation of photoexcited carriers on Bi2O3/TpBD-covalent organic framework S-scheme heterojunction for enhanced photocatalytic hydrogen production.

Abstract

Although covalent organic framework (COF) has emerged as promising photocatalysts for solar-driven H₂ evolution, it remains challenging to simultaneously achieve efficient charge-carrier separation, favorable redox potentials and high photocatalytic activity. Herein, we present a rationally designed Bi2O3/TpBD-covalent organic framework (COF; synthesized from 1,3,5-triformylphloroglucinol (Tp) and benzidine (BD)) heterojunction fabricated via a facile in-situ solvothermal strategy, which fundamentally overcomes the intrinsic limitations of pristine COF. Systematic photoelectrochemical analyses combined with density functional theory (DFT) calculations shows that intimate interfacial coupling between Bi2O3 and TpBD-COF establishes a built-in electric field-driven S-scheme charge migration pathway, effectively suppressing carrier recombination while simultaneously boosting redox thermodynamics. Strikingly, the optimized 30% Bi2O3/TpBD-COF heterojunction delivers an unprecedented H₂ production rate of 5.98 mmol g-1 h-1, representing a 49.8-fold enhancement over TpBD-COF and surpassing some of reported COF based photocatalytic systems. This study delivers a viable heterojunction-engineering strategy for developing advanced COF-based photocatalysts. It also yields in-depth mechanistic understanding of interfacial carrier behaviors, which facilitates the advancement of practical, high-performance solar-to-hydrogen conversion systems.