Defect-mediated Fermi level modulation boosting photo-activity of spatially-ordered S-scheme heterojunction.

Spatially-ordered S-scheme photocatalysts are intriguing due to their enhanced light harvesting, spatially isolated redox sites, and strong redox abilities. Nonetheless, heightening the performance of S-scheme photocatalysts via controllable defect engineering is still challenging to now. In this work, multi-armed MoSe/CdS S-scheme heterojunction with intimate Mo-S bond coupling and adjustable Se vacancies (V) and Mo concentrations was constructed, which consisted of few- or even single-layered MoSe growing on the {11-20} facets of wurtzite CdS arms. The S-scheme charge transmission mechanism of MoSe/CdS heterojunction was validated by density functional theory calculation combined with in situ photo-irradiated X-ray photoelectron spectroscopy, surface photovoltage, and radical measurements. Moreover, the Fermi level gap between CdS and MoSe was enlarged by regulating the contents of donor (V) and acceptor (Mo) impurities with synthesis temperature, which strengthens the built-in electric field and carriers transfer driving force of MoSe/CdS composites, contributing to an outstanding H evolution activity of 52.62 mmol·g·h (corresponding to an apparent quantum efficiency of 34.8 % at 400 nm) under visible-light irradiation (λ > 400 nm), 25.8 times that of Pt-loaded CdS counterpart and a substantial amount of reported CdS-containing photocatalysts. Our study results are anticipated to facilitate the rational design of advanced semiconductor nanostructures for efficient solar conversion and utilization.