Paper SS1+NC-ThA4
Water Diffusion on Pt(111) Terrace, Kink and Steps: Density Functional Theory Study of Water Interaction and Diffusion

Thursday, October 23, 2008, 3:00 pm, Room 207

Density functional theory (DFT PW91) calculations were used to study diffusion of water molecule on a flat Pt(111) terrace as well as on kinks and step edges. Diffusion on the (111) terrace is predicted to become active on the time scale of seconds at 74 K in reasonable agreement with experimental results (Daschbach et al. J. Chem. Phys. 120 (2004) 1516). The binding of water at steps and kinks on Pt(111) surface is substantially stronger than at the flat terrace, by 0.16 eV and 0.25 eV, respectively. The diffusion barriers of a single water molecule moving along the flat terrace up to a kink site or moving along the step edge are all comparable, while the barrier of diffusion up to a step edge is significantly lower then all of the other barriers calculated. Consequently, the barrier for diffusion from the step edge down to the terrace is substantially larger than for diffusion along the flat terrace. At low coverage, clusters of water molecules would, therefore, be expected to align along the upper side of step edges. This is consistent with experimental STM images taken by Morgenstern et al. (Morgenstern et al. Phys. Rev. Lett. 77 (1996) 703).