Hydrogen trapping at surface and subsurface vacancies of low-index surfaces of Pd

Abstract

Hydrogen segregation to vacancies in the surface and subsurface layers of (111) and (100) surfaces of Pd is studied in the density functional theory (DFT) approach. Adsorption energies and configurations of various clusters of H atoms at the vacancies are calculated. The adsorption energy varies for different sites in the vacancies with the distance to the surface from -0.26 eV (close to that of the bulk clusters) to -0.62 eV. Enhanced binding is found for the sites above the pores produced by vacancies in the subsurface layer. For the (111) surface vacancy the most favorable for segregation are tetrahedral lattice sites, while for (100) octa-sites have higher binding energy. Lattice relaxation effects are minor for the (111) surface but noticeably enhanced for the (100) surface. Hydrogen segregation to surface layer vacancies is accompanied with minimal charge transfer, which shows itself in cluster configurations. At high surface coverage the reduction of the cluster formation energy due to the H segregation should result in strongly enlarged concentration of the subsurface vacancy clusters, while the surface remains undamaged due to the prevailing surface adsorption.

H Resurface and Hot H Promoted H2 Recombination on Ni(111): Effects of Arrangement, Surface Coverage, and Lattice Motion

“…The hydrogenation reaction by a subsurface H is the most widely investigated surface–subsurface reaction by both experimental and theoretical methods. − Experimentally, Maynard et al reported that the absorption of atomic hydrogen on Ni(111) could be induced by exposure to atomic hydrogen. Premm et al observed three desorption states (at 185, 210, and 265 K) for the subsurface hydrogen on Ni(111).…”