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.

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.

No abstract

No abstract

Hexagonal boron nitride (hBN) has great potential as a promising gas barrier layer in proton exchange membrane fuel cells (PEMFCs) as it shows high proton conductivity as well as excellent gas‐blocking capability. However, structural defects and mechanical damage during the transfer of the hBN layer and membrane swelling have limited the application of hBN sheets to PEMFCs. Here, an ultrathin gas barrier layer is successfully fabricated on a proton exchange membrane via reconstruction of mechanically exfoliated hBN nanoflakes using a direct spin‐coating process. The hBN‐coated layer effectively suppresses the gas crossover and inhibits the formation of reactive oxygen radicals in the electrodes without reducing the proton conductivity of the membrane. It is also demonstrated that the structural advantages of hBN‐coated gas barrier layers promise high performance of a unit cell even after a open‐circuit voltage (OCV) hold test for 100 h. Furthermore, through in‐depth postmortem analyses, a time‐dependent degradation mechanism of membrane electrode assembly under the OCV condition is rationally proposed.