Engineering Semi-Reversed Quantum Well Photocatalysts for Highly-Efficient Solar-to-Fuels Conversion.

Semiconductor quantum wells (QWs) exhibit high charge-utilization efficiency for light-emitting applications due to their strong charge confinement effect. Inspired by this effect, herein, this work proposes a new idea to significantly improve the photo-generated charge separation for attaining a highly-efficient solar-to-fuels conversion process through "semi-reversing" the conventional QWs to confine only the photo-generated electrons. This electron confinement-improved charge separation is implemented in the well-designed model of the CdS/TiO 2 /CdS semi-reversed QW (SRQW) structure. The latter is fabricated by selectively assembling CdS quantum dots (QDs) onto the {101} facets (ultra-thin edge regions) of the TiO 2 nanosheets (NSs). Upon light excitation, the photo-generated electrons of SRQW can be confined on the TiO 2 -{101} facets in the vicinity of the CdS/TiO 2 hetero-interface. Thereby, the continuous multi-electron injection to the adsorbed reactants on the interfacial active-sites is significantly accelerated. Thus, the CdS/TiO 2 /CdS SRQW exhibits ≈35.7 and ≈56.0-fold enhancements on the photocatalytic activities for water and CO 2 reduction, respectively, compared to those of pure TiO 2 . Correspondingly, its CH 4 -product selectivity is increased by ≈180%. This work provides a novel charge separation mechanism, which is of great importance for the design of the next-generation quantum-sized photocatalysts for solar-to-fuels conversion.