MoS2 Quantum Dots: Effect of Hydrogenation on Surface Stability and H2S Release

We employ density functional theory to investigate effects of hydrogenation on the energetic stability and electronic properties of triangular MoS2 nanoclusters with S-edges. Excess edge sulfur atoms relative to the bulk stoichiometry along the edges are passivated by hydrogen atoms. We find that the hydrogen coverage for maximum stability can be calculated by (n - 2)/2(n - 1), where n is the number of S atoms along an edge. The energetics reveal a preference for the zigzag arrangement of adsorbed hydrogen atoms on the edges. Our calculations show vanishing HOMO-LUMO gaps mainly due to the presence of dangling bonds at the edges and can be considered metal-like. We find that the activation energy required to release H2S lies in between 0.47 and 0.62 eV, and this value is in good agreement with the recently reported experimental value.