Formation of Polysulfides from Consolidation of Cu Vacancies on CuS (001) Surfaces

Cu vacancies on CuS surfaces are very important for their properties, and the detailed structures are not very clear yet. In this study, we have systematically studied the structure and stability of CuS (001) surfaces with vacancies using the DFT + U method. The cleavage of CuS along the <001> direction affords a pair of asymmetric surfaces slab1 (featured by S2– on the surface) and slab2 (featured by S22– on the surface). Our calculation predicts that the surface defects would induce polysulfide formation on slab1 and the driving force increases with the concentration of the vacancies. As a comparison, the polysulfide formation on slab2 is much more challenging. Further mechanistic studies suggest that the polysulfide formation on slab1 is kinetically feasible. The electronic and geometric features of the polysulfide, as well as the difference between slab1 and slab2, have also been discussed in detail.