Single-Layer MoS2 with Sulfur Vacancies: Structure and Catalytic Application

Single-layer MoS2 is proving to be a versatile material for a wide variety of electronic, optical, and chemical applications. Sulfur depletion, without destabilization of the single layer, is considered a prudent way for making the basal plane of the layer catalytically active. Based on the results of our density-functional-theory examination of vacancy structures on one side of an MoS2 layer, we show that the formation energy per sulfur vacancy is the lowest (energetically favorable) when the vacancies form a row and that the longer the row, the lower the formation energy. In addition, we find that the lowest energy barrier for the diffusion of sulfur vacancy at the row structures through the exchange of a vacancy with a nearby sulfur atom is 0.79 eV and that this barrier increases as the row elongates. We also evaluate the propensity for catalytic activity of an MoS2 layer with two types of sulfur-vacancy structures (row and patch) and find the energetics for alcohol synthesis from syngas to be more favorable for the layer with a sulfur-vacancy patch.