Self-driven photochemical exfoliation of Fe-coordinated covalent organic frameworks for enhanced solar hydrogen production

Covalent organic frameworks (COFs) have great potential in solar hydrogen production to alleviate environmental pollution and global energy crisis. However, to achieve high H2 yield is still a challenge. Herein, we designed and synthesized two Fe3+-coordinated imine type COFs (Fe-COFs) for photocatalytic H2 production from water splitting. It was surprising to find that with the progress of H2 evolution under visible light, the bulk powders of Fe-COFs (180–250 nm) were gradually stripped into covalent organic nanosheets (Fe-CONs, 0.3–1.9 nm), which in turn efficiently catalyzed H2 production. As such, a self-driven mechanism was established in the catalytic system, and H2 evolution rate increased with the increase of cyclic runs until the thickness of the nanosheet no longer changes in the regeneration and reuse process of the Fe-CON photocatalysts. The optimal Fe-CON catalyst exhibited a record high H2 evolution rate of 67.94 mmol g−1h−1 among the currently reported COFs loaded with other non-noble metals, due to the more exposed active sites, smaller charge-transfer resistance, and stronger separation ability of the photogenerated electrons and holes of Fe-CONs. This work provides the first example for the integration of self-driven photochemical exfoliation of 2D materials and their highly efficient photocatalytic hydrogen evolution.