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 MoSe₂/CdS S-scheme heterojunction with intimate Mo-S bond coupling and adjustable Se vacancies (V_Se) and Mo⁵⁺ concentrations was constructed, which consisted of few- or even single-layered MoSe₂ growing on the {11-20} facets of wurtzite CdS arms. The S-scheme charge transmission mechanism of MoSe₂/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 MoSe₂ was enlarged by regulating the contents of donor (V_Se) and acceptor (Mo⁵⁺) impurities with synthesis temperature, which strengthens the built-in electric field and carriers transfer driving force of MoSe₂/CdS composites, contributing to an outstanding H₂ evolution activity of 52.62 mmol·g^-1·h^-1 (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.