Regulating Electron–Hole Separation to Promote Photocatalytic H₂ Evolution Activity of Nanoconfined Ru/MXene/TiO₂ Catalysts

A facile strategy for the preparation of a nanoconfined Ti3C2/Ru cocatalyst by direct reduction of Ru3+ ions without an additional reductant was developed. The in situ formation of TiO2 nanosheets on the Ti3C2/Ru surface ensures the separation of the semiconductor and cocatalyst (TiO2–Ti3C2/Ru), resulting in charge segregation and migration more effective than those achieved by traditionally prepared Ru–TiO2–Ti3C2. Owing to its low Fermi level, the self-assembled Ti3C2/Ru cocatalyst accepted the photogenerated electrons and promoted H2 evolution without an induction period, while exhibiting high surface structure stability. The changes in the work function and surface terminations of Ti3C2 during the photocatalysis were revealed by DFT calculations and in situ diffuse reflectance infrared Fourier transform spectroscopy. The efficient electron transfer enabled by the structurally separated Ti3C2/Ru-based photocatalyst significantly reduced the electron–hole recombination, increasing the photocatalytic H2 evolution activity. This work provides a guiding design approach for future solar energy conversion with the semiconductor–cocatalyst system.