Elizabeth Santos

Impedance studies of reconstructed and non-reconstructed gold single crystal surfaces

Abstract The (100), (111) and (210) surfaces of single crystal gold electrodes were investigated by impedance spectroscopy over the frequency range from 1 Hz to 10 kHz. In solutions containing weakly adsorbed anions, such as ClO 4 − , F − and PF 6 − , the data could be fitted to a simple equivalent circuit consisting of the double layer capacitance and the electrolyte resistance connected in series. Probably, the adsorption of these anions is so fast that it cannot be detected in the frequency range employed. In contrast, the anions Cl − and Br − adsorb more strongly and with a measurable rate; in this case an adsorption branch had to be added to the equivalent circuit. On Au(100) and Au(111) the well-known reconstruction phenomena were observed. Both the potentials at which they occur and the rate depend on the type and the concentration of the anion. The double layer capacity was measured on the reconstructed and on the ideal surfaces, and for a series of concentrations. In all cases considered, Parsons-Zobel plots are linear, but the slopes are much smaller than unity.

Recent Advances in Theoretical Aspects of Electrocatalysis

Although electrochemistry has much in common with surface science, the application of the principles of catalytic activity to the reactions taking place in an electrochemical environment is not straightforward. All electrochemical reactions of practical interest imply at least one step where an electron is transferred between species coming from the solution side or the electrode surface. Therefore electrochemical reactions occurring at the interfaces are governed by the interaction of the reactant both with the solvent and with the electrode. There is also an additional effect produced by the external applied potential, so that the Fermi level of the reactant can be easily tuned relative to the Fermi level of the electrode.

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.