Salt-Induced High-Density Vacancy-Rich 2D MoS 2  for Efficient Hydrogen Evolution.

Emerging non-noble metal 2D catalysts, such as molybdenum disulfide (MoS ₂ ), hold great promise in hydrogen evolution reactions. The sulfur vacancy is recognized as a key defect type that can activate the inert basal plane to improve the catalytic performance. Unfortunately, the method of introducing sulfur vacancies is limited and requires costly post-treatment processes. Here, a novel salt-assisted chemical vapor deposition (CVD) method is demonstrated for synthesizing ultrahigh-density vacancy-rich 2H-MoS ₂ , with a controllable sulfur vacancy density of up to 3.35 × 10 ¹⁴  cm ^-2 . This approach involves a pre-sprayed potassium chloridepromoter on the growth substrate. The generation of such defects is closely related to ion adsorption in the growth process, the unstable MoS ₂ -K-H ₂ O triggers the formation of sulfur vacancies during the subsequent transfer process, and it is more controllable and nondestructive when compared to traditional post-treatment methods. The vacancy-rich monolayer MoS ₂ exhibits exceptional catalytic activity based on the microcell measurements, with an overpotential of ≈158.8 mV (100 mA cm ^-2 ) and a Tafel slope of 54.3 mV dec ^-1 in 0.5 m H ₂ SO ₄ electrolyte. These results indicate a promising opportunity for modulating sulfur vacancy defects in MoS ₂ using salt-assisted CVD growth. This approach represents a significant leap toward achieving better control over the catalytic performances of 2D materials.
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