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 O2 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 O2 molecule chemisorbs on the Mo edge atoms with ΔE = −3.41 eV. The dissociation of O2 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 O2 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.