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/TiO2/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 TiO2 nanosheets (NSs). Upon light excitation, the photo‐generated electrons of SRQW can be confined on the TiO2‐{101} facets in the vicinity of the CdS/TiO2 hetero‐interface. Thereby, the continuous multi‐electron injection to the adsorbed reactants on the interfacial active‐sites is significantly accelerated. Thus, the CdS/TiO2/CdS SRQW exhibits ≈35.7 and ≈56.0‐fold enhancements on the photocatalytic activities for water and CO2 reduction, respectively, compared to those of pure TiO2. Correspondingly, its CH4‐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. The novel strategy of quantum‐confinement‐enhanced charge‐separation is proposed and demonstrated in the well‐designed model photocatalyst of CdS/TiO2/CdS semi‐reversed quantum‐well. This kind of promising photocatalysts is capable of not only confining the photo‐generated electrons nearby the hetero‐interfacial active‐sites, but also accelerating the electron injection to the adsorbed reactants on the interfacial active‐sites, thereby enhancing the photocatalytic activity for solar‐to‐fuels conversion.