Initial water adsorption on hematite (α -Fe<inf>2</inf>O<inf>3</inf>) (0001): A DFT + U study
Journal article, 2018
Interaction between water and oxide surfaces plays an important role in many applications. In the present study, we use a density functional theory + U method to study the initial adsorption behavior of water on various α-Fe 2 O 3 (0001) terminations. In particular, adsorption and dissociation of water at 1 monolayer and 0.5 monolayer coverage on the Fe-terminated, O-terminated, and ferryl-terminated (0001) surfaces are studied. The results show that the dissociated state is preferred, which is in agreement with theoretical and experimental observations. However, experiments show the co-existence of molecular water in the initial adsorption on hematite, which, so far, has no theoretical support. To explain this, we investigate OH-covered Fe-terminated surfaces and find that on R-Fe-(OH) x terminations, molecular water is actually energetically favorable. Thus, we propose that the existence of R-Fe-(OH) x terminations is a requirement for molecular water in the initial adsorption process. This proposal is further supported by comparing the calculated core level shift of R-Fe-(OH) x structures with experimental data.