Self‐Limited on‐Site Conversion of MoO₃ Nanodots into Vertically Aligned Ultrasmall Monolayer MoS₂ for Efficient Hydrogen Evolution

Abstract

MoS2 has emerged as a promising alternative electrocatalyst for the hydrogen evolution reaction (HER) due to high intrinsic per‐site activity on its edge sites and S‐vacancies. However, a significant challenge is the limited density of such sites. Reducing the size and layer number of MoS2 and vertically aligning them would be an effective way to enrich and expose such sites for HER. Herein, a facile self‐limited on‐site conversion strategy for synthesizing monolayer MoS2 in a couple of nanometers which are highly dispersed and vertically aligned on 3D porous carbon sheets is reported. It is discovered that the preformation of well‐dispersed MoO3 nanodots in 1–2 nm as limited source is the key for the fabrication of such an ultrasmall MoS2 monolayer. As indicated by X‐ray photoelectron spectroscopy and electron spin resonance data, these ultrasmall MoS2 monolayers are rich in accessible S‐edge sites and vacancies and the smaller MoS2 monolayers the more such sites they have, leading to enhanced electrocatalytic activity with a low overpotential of 126 mV at 10 mA cm−2 and 140 mV at 100 mA mg−1 for HER. This state‐of‐the‐art performance for MoS2 electrocatalysts enables the present strategy as a new avenue for exploring well‐dispersed ultrasmall nanomaterials as efficient catalysts.

Carbon‐Limited Conversion of Molybdenum Carbide into Curved Ultrasmall Monolayer Molybdenum Disulfide under Effects of ZrO2 Crystal Phases for Efficient Sulfur‐Resistant Methanation

“…The is more excited for terrace‐terminated structure, while the is preferentially excited for edge‐terminated structure from the previous report . The value of I A /I E (Intensity ration of and ) is 3.3 : 1 in S−Mo 2 C/M−ZrO 2 , clearly indicating that S−Mo 2 C/M−ZrO 2 is rich in edge‐terminated sites . Meanwhile, the value of Δκ (the distance between and , Δκ=ν ( )−ν ( )) can be used to identify the number of stacking layers of MoS 2.…”

“…For XPS spectra of S2s and S2p, the binding energy at 227.2 eV (S2s, Figure (a)) and 163.2 eV (S2p 3/2 , Figure (b)) are well assigned to the bridging and apical S 2− of MoS 2 , whereas the binding energy at 226.2 eV (S2s, Figure (b)) and 161.9 eV (S2p 3/2 ) are well attributed to terminal of MoS 2 , implying a considerable amount of edge sites exist . For S−Mo 2 C/T−ZrO 2 catalysts, only the binding energy at 160.5 eV (S2p 3/2 ) attributed to sulfidocarbide appears in Figure (b), indicating no MoS 2 species exists …”

“…concluded that exfoliated MoS 2 layer exhibited the highest activity by examined the different morphologies of MoS 2 catalysts . Vertically aligned MoS 2 catalyst with high dispersity produces rich edge sites and S‐vacancies, resulting in efficient hydrogen evolution activity . Similarly, small‐sized and highly dispersed MoS 2 catalysts will provide more active sites for sulfur‐tolerant methanation .…”

“…Generally, the catalytic performance of MoS 2 catalysts could be improved through reducing the particle size of MoS 2 , exfoliating its layers, increasing the dispersity of MoS 2 , as well as aligning them. [12][13][14][15][16][17][18] Therefore, it is necessary to understand the structure-activity relationship of MoS 2 catalysts for designing high performance catalyst. Eijsbouts et al reported that a strong correlation between edge sites of MoS 2 and catalytic activity.…”

Cobalt‐Embedded N‐Doped Carbon Arrays Derived In Situ as Trifunctional Catalyst Toward Hydrogen and Oxygen Evolution, and Oxygen Reduction

“…Figure b shows the Raman spectra of Co/MMCs and Co/CNWs. The G‐band located at 1586 cm −1 corresponds to the E 2g mode vibration of graphitic carbon, whereas the D‐band at 1347 cm −1 is associated with the defect mode . The ratio of I D /I G of Co/MMCs is 1.06, whereas which is 1.00 for Co/CNWs.…”