Germán Soldano

Hydrogen Electrocatalysis on Single Crystals and on Nanostructured Electrodes

We investigate hydrogen evolution on plain and nanostructured electrodes with a theory developed by us. On electrodes involving transition metals the most strongly adsorbed hydrogen is often only a spectator, while the reaction proceeds via a weakly adsorbed species. For Pt(111) the isotherms for both species are calculated. We explain why a nanostructure consisting of a monolayer of Pd on Au(111) is a good catalysts, and predict that Rh/Au(111) should be even better. Our calculations for a fair number of metals are in good agreement with experiment.

Recent Progress in Hydrogen Electrocatalysis

Recently, we have proposed a unified model for electrochemical electron transfer reactions which explicitly accounts for the electronic structure of the electrode. It provides a framework describing the whole course of bond-breaking electron transfer, which explains catalytic effects caused by the presence of surface d bands. In application on real systems, the parameters of this model—interaction strengths, densities of states, and energies of reorganization—are obtained from density functional theory (DFT). In this opportunity, we review our main achievements in applying the theory of electrocatalysis. Particularly, we have focused on the electrochemical adsorption of a proton from the solution—the Volmer reaction—on a variety of systems of technological interest, such as bare single crystals and nanostructured surfaces. We discuss in detail the interaction of the surface metal d band with the valence orbital of the reactant and its effect on the catalytic activity as well as other aspects that influence the surface-electrode reactivity such as strain and chemical factors.

Stability of Gold and Platinum Nanowires on Graphite Edges

The stability of coinage and noble metal nanowires supported on graphite steps is examined by density functional theory. In particular, we study the stability of supported gold and platinum wires and compare their chemical properties with those of surfaces and bare wires. A substantially stronger bond with graphite was found for platinum wires due to unfilled antibonding states, which are occupied in the case of gold. This difference has direct consequences for the adsorption of hydrogen. This reaction can occur either on the wire or directly on graphite steps. In the case of gold, the reaction is favoured on steps, while on platinum wires, it has no thermodynamical preferences. Our results suggest that, in early stages of wire formation, hydrogen could desorb gold from graphite, but not platinum.

Intrinsic stability and hydrogen affinity of pure and bimetallic nanowires.

A density functional theory study of the intrinsic stability of pure and bimetallic wires is presented. Several bimetallic combinations forming one-atom thick wires are studied. An explanation for the experimental instability of Cu wires in contrast to the stability of Au and Ag wires is given, which relies on the higher surface energy of the former. All the possible intercalations between Ni, Pd, Pt, Cu, Ag, and Au are studied. The bimetallic wires AuCu and AuAg were found to be the most stable ones. The reactivity of the latter two systems is also examined using hydrogen adsorption as a microscopic probe. It was found that at the inter-metal interface, up to second neighbors, Cu and Ag become more reactive and Au becomes more inert than the corresponding pure wires. These results are explained within the d-band model.