Why is gold such a good catalyst for oxygen reduction in alkaline media?

The two faces of gold: the reduction of oxygen on gold electrodes in alkaline solutions has been investigated theoretically. The most favorable reaction leads directly to adsorbed O(2)(-), but the activation energy for a two-step pathway, in which the first step is an outer-sphere electron transfer to give solvated O(2)(-), is only slightly higher. d-band catalysis, which dominates oxygen reduction in acid media, plays no role. The reason why the reaction is slow in acid media is also explained.

Ab initio studies of Ag-S bond formation during the adsorption of L-cysteine on Ag(111).

Ab initio studies of Ag-S bond formation during the adsorption of L-cysteine on Ag(111) have been performed by combining density functional theory with a quantum mechanical model developed in our group. The adsorbate-silver bond formation has been investigated by analyzing the projected density of states onto the different atoms of the molecule and by charge density difference calculations when the zwitterion radical approaches the surface. The polar character of the bond can be distinguished. For the first time, the coupling constants of the sulfur orbitals with the d and sp bands have been calculated by fitting the density of states. The role of the sp bands in the stabilization of the sulfur-silver bond is analyzed. The differences with the catalysis of hydrogen adsorption are discussed. Copper, gold, and silver are not good catalysts for the adsorption of hydrogen because of the position of the d bands lying too far below the Fermi level. However, the coin metals are excellent for the adsorption of thiols. The reason is that at the equilibrium position the sulfur atom is much farther from the surface than hydrogen, and thus the interactions with the sp bands stabilize its bond to the surface.

Ab initio studies of the electronic structure of L-cysteine adsorbed on Ag(111).

We have performed ab initio calculations for the adsorption of L-cysteine on Ag(111) using density functional theory. We have focused on two possible adsorbed species: the L-cysteine radical (•S-CH(2)-CH-NH(2)-COOH) adsorbed almost flat at a bridge site, slightly displaced toward an fcc location, and the zwitterionic radical Z-cysteine (•S-CH(2)-CH-NH(3)(+)-COO(-)) adsorbed at a bridge site, shifted to a hcp site forming a (4 × 4) unit cell (θ = 0.06) and a (√3 × âˆš3) R 30° unit cell (θ = 0.33), respectively. Special attention has been paid to the electronic structure of the system. The adsorbate-silver bond formation has been exhaustively investigated by analyzing the density of states projected onto the different atoms of the molecule, and by charge density difference calculations. A complicated interplay between sp and d states of silver in the formation of bonds between the adsorbates and the surface has been found. The role of the carboxyl group in the interaction with the surface has been also analyzed.

Silver electrodeposition on nanostructured gold: from nanodots to nanoripples.

Silver nanodots and nanoripples have been grown on nanocavity-patterned polycrystalline Au templates by controlled electrodeposition. The initial step is the growth of a first continuous Ag monolayer followed by preferential deposition at nanocavities. The Ag-coated nanocavities act as preferred sites for instantaneous nucleation and growth of the three-dimensional metallic centres. By controlling the amount of deposited Ag, dots of approximately 50 nm average size and approximately 4 nm average height can be grown with spatial and size distributions dictated by the template. The dots are in a metastable state. Further Ag deposition drives the dot surface structure to nanoripple formation. Results show that electrodeposition on nanopatterned electrodes can be used to prepare a high density of nanostructures with a narrow size distribution and spatial order.