Enhanced Photocatalytic Charge Separation in Coating-Protected Porous Silicon Quantum Dot Films With Stability Approaching 100 Hours

Quantum dot (QD) photocatalysts, with tunable bandgaps enabled by quantum confinement, are promising for photocatalytic hydrogen evolution reactions (HER), but developing an efficient, low-cost, and stable porous support with high catalyst loading capacity and high quantum efficiency remains a challenge. We use atomic layer deposition (ALD) to double-coat Si QD films with 2 nm Al₂O₃ and 5 nm TiO₂, inhibiting native oxide formation and suppressing Si-OH formation in water. Si QD films with Al₂O₃ interlayers show higher HER rates (0.15 µmol cm⁻² h⁻¹) than those with only TiO₂ coating (0.08 µmol cm⁻² h⁻¹) and can maintain their activity for at least 72 h of photocatalytic H₂ production. A superior internal quantum efficiency of 14.1 % at 400 ± 10 nm is demonstrated using Al₂O₃/TiO₂ double-layer coated Si QD photocatalysts under optimal operation. This research demonstrates that ALD TiO₂ coating of appropriate thickness enables efficient band-like hole charge transport and facilitates electron hopping, while the Al₂O₃ coating suppresses electron–hole recombination and facilitates charge transfer via tunneling. These findings provide a foundation for developing efficient, stable few-nm particulate photocatalysts for light-driven catalysis.