Hydrogen Electrode Reaction: electrocatalytic activity of metal surfaces

PAOLA QUAINO; ELISABETH SANTOS; WOLFGANG SCHMICKLER

Krakow

Congreso; 7th Spring Meeting of the International Society of Electrochemistry; 2009

The International Society of Electrochemistry - ISE

Due to progress in the theory of electrocatalysis and in quantum chemistry it has become possible to investigate the hydrogen reaction and perform quantitative calculations for the reaction rate. We demonstrate this with model calculations for the adsorption of hydrogen on Pt(111). The theory that we apply rests in a recently developed model for electrocatalysis, which combines results of quantum chemical calculations to obtain systems parameters. The theory itself is based on a Hamiltonian devised by Santos, Koper and Schmickler. It incorporates elements of the theories of Marcus and of the Anderson-News model, and provides a framework both for simple and for bond-breaking electron transfer.In order to calculate the free energy surface for the adsorption of hydrogen, we calculate the adsorption energy of the atom for the equilibrium distance in a fcc hollow site, and for a series of position vertically above this site. For each distance we also calculate the density of states projected onto the 1s orbital of hydrogen, which we fit to the model.In addition, we are trying to undestand the elementary processes involved in the hydrogen electrode reaction and identify active sites for the adsorbed species (Hupd and Hopd).Our results show that the center of the hydrogen 1s orbital lies somewhat bellow the d band of platinum, but its DOS overlaps with this band. Thus, according with experimental data, our calculations indicate that the adsorption starts at potentials above the equilibrium potential and with an almost vanishing energy of activation