Abstract: Two-dimensional (2D) heterojunctions are promising photocatalysts for hydrogen production due to their unique ability to efficiently convert solar energy to green fuels. In this work, an S-scheme 2D/2D F-TiO₂/CdS heterostructure was designed and synthesized via a facile hydrothermal method. The hydrogen evolution rate of optimal F-TiO₂/CdS photocatalyst irradiated with simulated sunlight reached to 1.7 mmol g^-1 h^-1, which was about 7 times that of pristine CdS nanosheets, 1.5 times that of TiO₂ nanoparticles composited with CdS nanosheets, and the apparent quantum efficiency at 420 nm was 4.3 %. The in-situ Kelvin probe force microscopy results showed that the built-in electric field strength (BIEF) of 2D/2D F-TiO₂/CdS is about 6.2 × 10³ V cm^-1 under the dark condition, which is about 2.3 times that of TiO₂ nanoparticles composited with CdS nanosheets. Moreover, in-situ electron paramagnetic resonance results showed that the valence band position of F-TiO₂ is more positive and showed a clear signal peak, suggesting that F-TiO₂ could generate more hydroxyl radicals. When F-TiO₂ contacts with CdS, the signals of both radicals are significantly enhanced, indicating that the reducing ability of CdS and the oxidizing ability of F-TiO₂ are well preserved. These results verify that S-scheme 2D/2D F-TiO₂/CdS processes stronger BIEF, which could effectively enhance the photocatalytic hydrogen production activity.

Key words: Photocatalyst, H₂ production, F-doped TiO₂ /CdS, Built-in electric field