The hydrogen economy is seen as a potential alternative to overcome the depletion of traditional fossil fuels and environmental pollution; therefore, the demand for high-purity hydrogen has rapidly increased. To produce hydrogen in a sustainable and environmentally friendly manner, numerousThe metallic 1T phase of WS 2 (1T-WS 2 ), which boosts the charge transfer between the electron source and active edge sites, can be used as an efficient electrocatalyst for the hydrogen evolution reaction (HER). As the semiconductor 2H phase of WS 2 (2H-WS 2 ) is inherently stable, methods for synthesizing 1T-WS 2 are limited and complicated. Herein, a uniform wafer-scale 1T-WS 2 film is prepared using a plasma-enhanced chemical vapor deposition (PE-CVD) system. The growth temperature is maintained at 150 °C enabling the direct synthesis of 1T-WS 2 films on both rigid dielectric and flexible polymer substrates. Both the crystallinity and number of layers of the as-grown 1T-WS 2 are verified by various spectroscopic and microscopic analyses. A distorted 1T structure with a 2a 0 × a 0 superlattice is observed using scanning transmission electron microscopy. An electrochemical analysis of the 1T-WS 2 film demonstrates its similar catalytic activity and high durability as compared to those of previously reported untreated and planar 1T-WS 2 films synthesized with CVD and hydrothermal methods. The 1T-WS 2 does not transform to stable 2H-WS 2 , even after a 700 h exposure to harsh catalytic conditions and 1000 cycles of HERs. This synthetic strategy can provide a facile method to synthesize uniform 1T-phase 2D materials for electrocatalysis applications.
Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted considerable attention owing to their synergetic effects with other 2D materials, such as graphene and hexagonal boron nitride, in TMD-based heterostructures. Therefore, it is important to understand the physical properties of TMD–TMD vertical heterostructures for their applications in next-generation electronic devices. However, the conventional synthesis process of TMD–TMD heterostructures has some critical limitations, such as nonreproducibility and low yield. In this paper, we synthesize wafer-scale MoS2–WS2 vertical heterostructures (MWVHs) using plasma-enhanced chemical vapor deposition (PE-CVD) via penetrative single-step sulfurization discovered by time-dependent analysis. This method is available for fabricating uniform large-area vertical heterostructures (4 in.) at a low temperature (300 °C). MWVHs were characterized using various spectroscopic and microscopic techniques, which revealed their uniform nanoscale polycrystallinity and the presence of vertical layers of MoS2 and WS2. In addition, wafer-scale MWVHs diodes were fabricated and demonstrated uniform performance by current mapping. Furthermore, mode I fracture tests were performed using large double cantilever beam specimens to confirm the separation of the MWVHs from the SiO2/Si substrate. Therefore, this study proposes a synthesis mechanism for TMD–TMD heterostructures and provides a fundamental understanding of the interfacial properties of TMD–TMD vertical heterostructures.
The octahedral structure of 2D molybdenum disulfide (1T‐MoS2) has attracted attention as a high‐efficiency and low‐cost electrocatalyst for hydrogen production. However, the large‐scale synthesis of 1T‐MoS2 films has not been realized because of higher formation energy compared to that of the trigonal prismatic phase (2H)‐MoS2. In this study, a uniform wafer‐scale synthesis of the metastable 1T‐MoS2 film is performed by sulfidation of the Mo metal layer using a plasma‐enhanced chemical vapor deposition (PE‐CVD) system. Thus, plasma‐containing highly reactive ions and radicals of the sulfurization precursor enable the synthesis of 1T‐MoS2 at 150 °C. Electrochemical analysis of 1T‐MoS2 shows enhanced catalytic activity for the hydrogen evolution reaction (HER) compared to that of previously reported MoS2 electrocatalysts 1T‐MoS2 does not transform into stable 2H‐MoS2 even after 1000 cycles of HER. The proposed low‐temperature synthesis approach may offer a promising solution for the facile production of various metastable‐phase 2D materials.
Using tungsten disulfide (WS 2 ) as a hydrogen evolution reaction (HER) electrocatalyst brought on several ways to surpass its intrinsic catalytic activity. This study introduces a nanodomain tungsten oxide (WO 3 ) interface to 1T-WS 2 , opening a new route for facilitating the transfer of a proton to active sites, thereby enhancing the HER performance. After H 2 S plasma sulfurization on the W layer to realize nanocrystalline 1T-WS 2 , subsequent O 2 plasma treatment led to the formation of amorphous WO 3 (a-WO 3 ), resulting in a patchwork-structured heterointerface of 1T-WS 2 /a-WO 3 (WSO). Addition of a hydrophilic interface (WO 3 ) facilitates the hydrogen spillover effect, which represents the transfer of absorbed protons from a-WO 3 to 1T-WS 2 . Moreover, the faster response of the cathodic current peak (proton insertion) in cyclic voltammetry is confirmed by the higher degree of oxidation. The rationale behind the faster proton insertion is that the introduced a-WO 3 works as a proton channel. As a result, WSO-1.2 (the ratio of 1T-WS 2 to a-WO 3 ) exhibits a remarkable HER activity in that 1T-WS 2 consumes more protons provided by the channel, showing an overpotential of 212 mV at 10 mA/cm 2 . Density functional theory calculations also show that the WO 3 phase gives higher binding energies for initial proton adsorption, while the 1T-WS 2 phase shows reduced HER overpotential. This improved catalytic performance demonstrates a novel strategy for water splitting to actively elicit the related reaction via efficient proton transport.
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