Hydrogen evolution and Cu UPD at stepped gold single crystals modified with Pd

The evolution of hydrogen on Au(332) and Au(665) surfaces modified with Pd was studied by cyclic voltammetry in hydrogen-saturated sulfuric acid. A strong catalytic activity of Pd decorating the steps, and even monoatomic rows, reflected in the exchange current density for the hydrogen evolution reaction, was found. In comparison, the activity of Pd at terrace sites is negligible. This is explained by the previously observed weak adsorption of hydrogen at monoatomic Pd rows according to the Sabatier principle. For Au(665)/Pd electrodes where the Pd steps have been blocked with Cu, the catalytic activity decreases to values in the same order of magnitude of those for Au(665) surfaces modified with more than a full monolayer of Pd. No direct evidence of hydrogen spillover from Pd-covered areas to the Au substrate was found. Cu underpotential deposition measurements also suggest that no alloy formation takes place between the Cu atoms and the underlying Pd film, nor between Pd and the gold substrate. Dedicated to Professor Dr. Algirdas Vaskelis on the occasion of his 70th birthday.