Theoretical study of the MoS2 (100) surface:: A chemical potential analysis of sulfur and hydrogen coverage

The stability of the (100) MoS2 surface has been studied using periodic DFT calculations taking into account various parameters such as the temperature and the partial pressure ratios of H-2 and H2S present in the surrounding atmosphere. It appears that the sulfur coverage of the surface is strongly dependent on the H-2/H2S ratio and that under working conditions, the most stable surface does not contain any coordinately unsaturated sites (CUS). Direct comparisons with experimental literature data such as EXAFS or TPR measurements show a good agreement between calculations and these experiments. The second part of the study deals with the behavior of hydrogen on the surfaces. The endothermic dissociation always leads to Mo-H and S-H groups. This implies that hydrogen is not stable on the MoS2 surface unless at very high pressure or very low temperature. Furthermore, H-2 dissociation on the surface will not lead to the formation of CUS.