Salt-Induced High-Density Vacancy-Rich 2D MoS₂ for Efficient Hydrogen Evolution.

Abstract

Emerging non-noble metal 2D catalysts, such as molybdenum disulfide (MoS₂), 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-MoS₂, with a controllable sulfur vacancy density of up to 3.35 × 10¹⁴ 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 MoS₂-K-H₂O 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 MoS₂ 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 H₂SO₄ electrolyte. These results indicate a promising opportunity for modulating sulfur vacancy defects in MoS₂ using salt-assisted CVD growth. This approach represents a significant leap toward achieving better control over the catalytic performances of 2D materials.