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

Abstract 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.