*

Molybdenum disulfide (MoS₂) is a promising nonprecious catalyst for catalyzing electrochemical hydrogen (H2) production from water. Previous studies have indicated that the edge sites and sulfur vacancies are the most-probable active sites for the hydrogen evolution reaction (HER). However, their microscopic origin remains elusive. In this talk, we will present a microscopic model explaining the variation in the free energy of H-absorption at different sites. The results are obtained from first principles calculations using SCAN meta-GGA functional. We find that the energy difference between the lowest unoccupied states and the H-associated anti-bonding states dominates the H-adsorption. The larger the difference, the stronger the H adsorption becomes. The guiding principles emerging from this understanding will be discussed for improving the HER in MoS₂ and designing new HER catalyst.