(Top panel) Geometry of the solid precursors and the growth steps with and without a membrane, respectively. Blue-, yellow-, and wine-filled circles stand for Mo, S, and V atoms, respectively. (Bottom panel) V–Svac pairs as the active site for selective CO2 reduction to CO.
This research presents a practical method for incorporating vanadium into atomically thin hexagonal MoS2, with the objective of enhancing its optoelectronic properties. The primary motivation behind this study is to develop more efficient photocatalysts for the reduction of CO2 in the gas phase, addressing the critical issue of rising atmospheric CO2 levels.
To achieve this, the authors employed a capped, or membrane-controlled, vapor–liquid–solid (VLS) growth technique. This approach enables the production of wafer-scale, continuous ultrathin Mo1-xVxS2 alloy films that feature sulfur vacancies (Svac). Compared to previous methods, this technique significantly enhances vanadium incorporation, thus addressing a major limitation in controlling the alloying process.
The research, published in ACS Nano, involved careful optimization of several growth parameters, such as the thickness of the SiO2 capping layer, growth temperature, and the dimensions of the solid precursors confined within a nanometer-scale environment. The SiO2 membrane plays crucial roles throughout the growth process: it prevents the escape of vanadium-containing species, supplies sulfur and hydrogen to the molten phase via gas diffusion, and promotes uniform, symmetric two-dimensional grain growth across the substrate.
Microscopy analyses and theoretical calculations indicate a strong correlation between the presence of vanadium atoms and the density of sulfur vacancies, with increasing vanadium content resulting in a higher vacancy density. This pairing of vanadium and sulfur vacancies leads to charge transfer from vanadium to adjacent sulfur and molybdenum atoms, resulting in pronounced photoluminescence quenching and modifications to the electronic states.
As a photocatalyst, bilayer Svac–Mo1-xVxS2 achieved a CO2-to-CO conversion rate approximately five times greater than that of pristine MoS2 when exposed to simulated sunlight. The internal quantum efficiency (IQE) reached around 0.017%, with the catalyst demonstrating stability for at least 20 hours. The enhanced catalytic activity is largely attributed to the formation of V–Svac active sites, which improve light absorption in the visible spectrum, alter the band structure, and facilitate charge transfer and transport.
Prof. Li-Chyong Chen, co-corresponding author of the study from Center for Condensed Matter Sciences at National Taiwan University, says, “These findings underscore the potential of employing defect–dopant engineering as an effective strategy for developing advanced photocatalysts for artificial photosynthesis and carbon-neutral energy solutions.”
Prof. Li-Chyong Chen's email address: [email protected]
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