Oxidation of Mo-Terminated Pit Edges in MoS2 Monolayer

We employed ab initio molecular dynamics simulations to investigate the oxidation of MoS2 triangular pits with oxidized zz-Mo edges. The purpose of this work is to characterize advanced stages of oxidation at high temperatures, which lead to the desorption of SO2 and the formation of oxy-thiomolybdate complexes. We first consider the energetics of the interaction of O-2 with the Mo atoms of the pit edge and then we calculate activation energy barriers for the initial stages of oxidation, after the dissociative adsorption of oxygen. The O-2 molecule chemisorbs on the Mo edge atoms with Delta E = -3.41 eV. The dissociation of O-2 has a low energy barrier of 0.71 eV which opens pathways for further oxidation processes. The ab-initio molecular dynamics simulations show that the breakage of the O-O bond of chemisorbed O-2 molecules on the Mo edge atoms gives rise to MoO2 and MoO3 moieties along the edges of the pit. As O atoms diffuse and insert into Mo-S bonds, the desorption of SO2 is first observed. Further oxidation leads to the formation of surface oxy-thiomolybdate (Mo2S3O5, Mo2S2O5, Mo3S3O3, etc.) complexes which finally desorb from the surface at high temperatures.