Advancing the Understanding of the Structure-Activity-Durability Relation of 2D MoS₂ for the Hydrogen Evolution Reaction

It has been decades since electrochemical water splitting was proposed as a promising strategy for renewable hydrogen production. Transition-metal dichalcogenides offer cheap, earth-abundant catalyst candidates for the hydrogen evolution reaction (HER). Among those, molybdenum disulfide (MoS₂) has been the subject of a vast number of studies, where different approaches such as manipulating the type and number of layers, or density of the intrinsic active sites, and engineering compositional phase and structure have been employed to enhance the electrochemical activity. Herein, we show the HER activities of two-dimensional 1T- and 1H-MoS₂ mixed phases with respect to the pure 1H-MoS₂ scale with the 1T phase. The creation of S vacancies in 1H-MoS₂ enhances HER activities. Further enhancement in the activity is achieved by N doping induced by N₂ plasma exposure owing to the formation of a metallic 1T phase and S vacancies. The spectroelectrochemical Raman spectroscopy and ex-situ X-ray photoelectron spectroscopy investigations reveal a gradual phase conversion induced by H adsorption during electrochemical tests. The 1T to 1H phase transformation results in a significant loss in HER activity.