Visualization of environment-dependent carrier dynamics on 2D transition metal dichalcogenides using ultrafast pump-probe microscopy

Recently, the great economic and environmental interest for the production of the clean fuel hydrogen through water splitting is worldwide promoted, practically using 2D transition metal dichalcogenides (TMDs), e.g., MoS
2
. In this study, we investigated the ultrafast carrier dynamics of MoS
2
in air and liquid. Moreover, we also in situ probed the ultrafast carrier dynamics at 2D atomic layer MoS
2
/liquid electrolyte interface for hydrogen evolution reaction (HER). The several-picoseconds relaxation component in transient transmittance changes ($\Delta T/T$) has been identified to indicate the catalytic activation time and shows the distribution of activation sites during HER.