The oxidation and evolution reactions of hydrogen are investigated at nanostructures of palladium-gold combining experimental and theoretical approaches. The extraordinary reactivity of submonolayers of Pd on Au(1 1 1) has been explained by a direct correlation with the changes in the electronic properties and geometrical arrangements. The application of the electrocatalysis theory, which goes beyond the qualitative approach of the d band centers, allows explaining quantitatively the experimental finding. (C) 2011 Elsevier B. V. All rights reserved.