Revealing the dynamics of charge carriers in organic/inorganic hybrid FS-COF/WO3 S-scheme heterojunction for boosted photocatalytic hydrogen evolution

Designing high-efficiency photocatalysts by the construction of organic/inorganic heterojunctions is considered to be an effective approach for improving photocatalytic hydrogen evolution reaction (HER) activity. This work designed and built unique S-scheme heterojunctions by in-situ growing inorganic WO3 nanoparticles with excellent oxidation ability on fused-sulfone-modified covalent organic frameworks (FS-COF) with strong reduction ability. It is found that FS-COF and WO3 have a well-matched staggered band alignment. The best-designed FS-COF/WO3-20% exhibits a maximum photocatalytic HER rate of 24.7 mmol g-1 h-1 under visible light irradiation, which is 1.4 times greater than the pure FS-COF. Moreover, photogenerated electron-hole pairs can be separated and utilized more efficiently thanks to the FS-COF/WO3 heterojunction's ability to create a favorable internal electric field resulting from the difference in work functions between FS-COF and WO3, which speeds up the transfer dynamics of photoinduced electrons from WO3 to FS-COF through an additional interfacial electron-transfer channel obeying the directional S-scheme migration mechanism. Furthermore, the S-scheme migration mechanism of photoinduced charge carriers instead of the type-II mechanism was confirmed by the signal intensity of •O2− species from spin-trapping electron paramagnetic resonance (EPR) spectra over the single component and the formed heterojunction. It ensures the photoexcited electrons maintain on the lowest unoccupied molecular orbital (LUMO) of FS-COF with a strong reduction ability to participate in photocatalytic HER, resulting in a significantly boosted H2 evolution rate. Based on organic/inorganic coupling, this work offers a strategy for creating particular S-scheme heterojunction photocatalysts.