Activation of nitrogen species mixed with Ar and H2S plasma for directly N-doped TMD films synthesis

Abstract

Among the transition metal dichalcogenides (TMD), tungsten disulfide (WS₂) and molybdenum disulfide (MoS₂) 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 WS₂ and MoS₂, while their basal planes are inert. We propose a novel process for N-doped TMD synthesis for advanced HER using N₂ + Ar + H₂S plasma. The high ionization energy of Ar gas enabled nitrogen species activation results in efficient N-doping of TMD (named In situ-MoS₂ and In situ-WS₂). In situ-MoS₂ and WS₂ 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-MoS₂) and 298 mV (In situ-WS₂) at a current density of 10 mA cm^-2, which are lower than those of pristine MoS₂ and WS₂, 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.