Transient phase transition during the hydrogen evolution reaction

2H-MoS2 is one of the most promising noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER). A widely accepted view on its HER mechanism is that its edge sites possess a high HER activity, whereas its basal plane is inert during the HER. Here, we confirm that this view is problematic. Results based on first-principles calculations as well as in situ attenuated total reflection surface enhanced infrared absorption spectroscopy and X-ray absorption fine structure measurements identify transient phase-transition behaviour, which enables the partial basal plane of 2H-MoS2 to exhibit high HER activity. Specifically, during the HER, MoS2 can undergo a local phase transition from the inert 2H phase for the HER to the 1T & PRIME; phase with high HER activity, and the phase transition is transient-it recovers to the 2H phase after the reaction. This work reports a new reaction mechanism (i.e., the transient phase transition) and thus provides new opportunities for heterogeneous electrocatalyst design and mechanistic investigations into heterogeneous electrocatalysis.

Automated summary

By using first-principles calculations, in situ attenuated total reflection surface enhanced infrared absorption spectroscopy and X-ray absorption fine structure measurements, this study identifies a transient phase-transition behavior in 2H-MoS2, which enables its basal plane to exhibit high HER activity. This discovery provides new opportunities for designing heterogeneous electrocatalysts and investigating the mechanistic process of heterogeneous electrocatalysis.