Exploring the Evolution Mechanism of Sulfur Vacancies by Investigating the Role of Vacancy Defects in the Interaction between HS and the FeS(001) Surface.

Vacancy defects are inherent point defects in materials. In this study, we investigate the role of Fe vacancy (V) and S vacancy (V) in the interaction (adsorption, dissociation, and diffusion) between HS and the FeS(001) surface using the dispersion-corrected density functional theory (DFT-D2) method. V promotes the dissociation of HS but slightly hinders the dissociation of HS. Compared with the perfect surface (2.08 and 1.15 eV), the dissociation energy barrier of HS is reduced to 1.56 eV, and HS is increased to 1.25 eV. Meanwhile, S vacancy (V) significantly facilitates the adsorption and dissociation of HS, which not only reduces the dissociation energy barriers of HS and HS to 0.07 and 0.11 eV, respectively, but also changes the dissociation process of HS from an endothermic process to a spontaneous exothermic one. Furthermore, V can promote the hydrogen (H) diffusion process from the surface into the matrix and reduce the energy barrier of the rate-limiting step from 1.12 to 0.26 eV. But it is very hard for H atoms gathered around V to diffuse into the matrix, especially the energy barrier of the rate-limiting step increases to 1.89 eV. Finally, we propose that V on the FeS(001) surface is intensely difficult to form and exist in the actual environment through the calculation results.