Hydrogen diffusion on the tin-covered tungsten surface: A first-principles study

The diffusion behavior of hydrogen (H) on tin-covered tungsten (Sn-W) surfaces is of great significance for understanding the retention of H in Sn-W materials exposed to H plasma. In this work, the diffusion mechanism of H in Sn-W surfaces and the related interactions were studied through employing density functional theory. The results show that Sn atoms are strongly adsorbed on the W surface with energy of-5.10 similar to-5.60 eV with surface reconstruction for W (100). The diffusion of H atom from top of Sn to inte-rior on W (100) and W (110) surface requires energy barrier of at least 1.02 eV and 0.76 eV, respectively. More interestingly, the Sn converging on W surface can reduce the diffusion energy barriers of H atom on or into the W surface, which indicates that the diffusion of H atom became easier in comparison to naked W surface. The facilitation effect of Sn on H atom diffusion can be attributed to the strong inter-action between the Sn atom and W surface as proved by the calculated charge density and interaction energy. However, the coverage of Sn has little impact on the diffusion of H atom on or into the W sub-surface. As the depth increases, the influence of surface Sn atoms on the diffusion barrier of H decreases. The influence of liquid tin on the diffusion of hydrogen in solid tungsten will be helpful to understand the abnormal retention mechanism for liquid metal divertor.(c) 2023 Published by Elsevier B.V.