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Among the transition metal dichalcogenides (TMD), tungsten disulfide (WS 2 ) and molybdenum disulfide (MoS 2 ) are promising sulfides for replacing noble metals in the hydrogen evolution reaction (HER) owing to their abundance and good catalytic activity. However, the catalytic activity is derived from the edge sites of WS 2 and MoS 2 , while their basal planes are inert. We propose a novel process for N-doped TMD synthesis for advanced HER using N 2  + Ar + H 2 S plasma. The high ionization energy of Ar gas enabled nitrogen species activation results in efficient N-doping of TMD (named In situ-MoS 2 and In situ-WS 2 ). In situ-MoS 2 and WS 2 were characterized by various techniques (Raman spectroscopy, XPS, HR-TEM, TOF-SIMS, and OES), confirming nanocrystalline and N-doping. The N-doped TMD were used as electrocatalysts for the HER, with overpotentials of 294 mV (In situ-MoS 2 ) and 298 mV (In situ-WS 2 ) at a current density of 10 mA cm -2 , which are lower than those of pristine MoS 2 and WS 2 , respectively. Density functional theory (DFT) calculations were conducted for the hydrogen Gibbs energy (∆G H ) to investigate the effect of N doping on the HER activity. Mixed gas plasma proposes a facile and novel fabrication process for direct N doping on TMD as a suitable HER electrocatalyst., (© 2022. The Author(s).)

Nanostructural modification of two-dimensional (2D) materials has attracted significant attention for enhancing hydrogen evolution reaction (HER) activity. In this study, the nanostructure of TaS 2 films was controlled by controlling the Ar/H 2 S gas ratio used in plasma-enhanced chemical vapor deposition (PECVD). At a high Ar/H 2 S gas ratio, vertically aligned TaS 2 (V-TaS 2 ) films were formed over a large-area (4 in) at a temperature of 250 °C, which, to the best of our knowledge, is the lowest temperature reported for PECVD. Furthermore, the plasma species formed in the injected gas at various Ar/H 2 S gas ratios were analyzed using optical emission spectroscopy to determine the synthesis mechanism. In addition, the 4 in wafer-scale V-TaS 2 was analyzed by x-ray photoelectron spectroscopy, transmission electron microscopy, and atomic force microscopy, and the HER performance of the as-synthesized TaS 2 fabricated with various Ar/H 2 S ratios was measured. The results revealed that, depending on the film structure of TaS 2 , the HER performance can be enhanced owing to its structural advantage. Furthermore, the excellent stability and robustness of V-TaS 2 was confirmed by conducting 1000 HER cycles and post-HER material characterization. This study provides important insights into the plasma-assisted nanostructural modification of 2D materials for application as enhanced electrocatalysts., (© 2021 IOP Publishing Ltd.)