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

Emerging non-noble metal two-dimensional catalysts, such as molybdenum disulfide (MoS 2 ), hold great promise in hydrogen evolution reactions. To enhance the intrinsically low activity of the basal plane structures of MoS 2 , various phase, strain and defect engineering approaches have been proposed. Sulfur vacancy is recognized as a key type of defect that impacts the catalytic performance. Unfortunately, the method of introducing sulfur vacancies is limited and requires costly post-treatment processes. Here, we demonstrate a novel salt-assisted chemical vapor deposition (CVD) method for synthesizing ultra-high-density vacancy-rich 2H-MoS 2 , with a controllable sulfur vacancy density of up to 3.35 × 10 14 cm -2 . Our approach involves pre-sprayed potassium chloride (KCl) promoter 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 vacancy during the subsequent transfer process. Our novel approach to directly implant high density S vacancies in MoS 2 during growth is more controllable and nondestructive when compared to the 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. Our results indicate a promising opportunity for modulating pure sulfur vacancy defects in MoS 2 using salt-assisted CVD growth. This approach represents a significant leap towards achieving better control over the catalytic performances of 2D materials. This article is protected by copyright. All rights reserved.