Representative configurations for a Ag31Pt69/Pt ). For Pt(Pt6) ensembles this amounts to about 0.1 eV (Figure ). Similar variations, though less pronounced, are obtained also for the other heptamer types. Furthermore, over the entire composition range considered, up to about 60% surface Ag, OH binding is weaker on the Pt(Pt6) ensembles than on Pt , while for the other heptamer types it is stronger than on Pt . Hence, regardless of the configuration, the ORR activity is dominated by reaction on Pt(Pt6) heptamers, and the enhanced activity of these binary surface alloys as compared to Pt(111) results from long-range strain effects self-induced by the surface. The Ag surface atoms in the unit cell outside the Pt(Pt6) heptamers lead to an anisotropic compression of the Pt-Pt bonds in the Pt(Pt6) heptamer, and thus in a strain induced increase of the ORR activity. Additional electronic ligand effects and strain effects, in addition to the Ag-induced long-range strain effects in the Pt(Pt6)