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 Al 2 O 3 and 5 nm TiO 2 , inhibiting native oxide formation and suppressing Si‐OH formation in water. Si QD films with Al 2 O 3 interlayers show higher HER rates (0.15 µmol cm −2 h −1 ) than those with only TiO 2 coating (0.08 µmol cm −2 h −1 ) and can maintain their activity for at least 72 h of photocatalytic H 2 production. A superior internal quantum efficiency of 14.1 % at 400 ± 10 nm is demonstrated using Al 2 O 3 /TiO 2 double‐layer coated Si QD photocatalysts under optimal operation. This research demonstrates that ALD TiO 2 coating of appropriate thickness enables efficient band‐like hole charge transport and facilitates electron hopping, while the Al 2 O 3 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.