Enrique Herrero was born in Salamanca, Spain, in 1967. He received his B.S. in Chemistry from the University of Alicante (Spain) in 1990. His graduate thesis dealt with the oxidation of methanol, formic acid, and CO on platinum single crystals and was completed in 1995 at the University of Alicante under the direction of Prof. Juan M. Feliu. During this time he spent one year working with Prof. Andrzej Wieckowski at the University of Illinois at Urbana-Champaign. In 1996 he went on to a postdoctoral appointment in the group of Prof. He ´ctor D. Abrun ˜a in the Chemistry Department at Cornell University, where he worked on metal deposition on single crystals. He is currently an assistant professor at the University of Alicante. Lisa Buller received a B.S. in Chemistry from the University of WisconsinsMadison in 1992. She obtained a Ph.D. in Chemistry from Cornell University in 1997 under the direction of Prof. H. D. Abrun ˜a. Her thesis work dealt with electrochemical and X-ray studies of metal deposition onto single crystals. She is currently an assistant professor at the University of WisconsinsPlatteville.

The quantitative analysis of the different surface sites on platinum samples is attempted from pure voltammetric data. This analysis requires independent knowledge of the fraction of two-dimensional (111) and (100) domains. Specific site-probe reactions are employed to achieve this goal. Irreversibly-adsorbed bismuth and tellurium have been revealed to be sensitive to the presence of (111) terrace domains of different width whereas almost all sites involved in (100) ordered domains have been characterized through germanium adatoms. The experimental protocol follows that used with well-defined single-crystal electrodes and, therefore, requires careful control of the surface cleanliness. Platinum basal planes and their vicinal stepped surfaces have been employed to obtain calibration plots between the charge density measured under the adatom redox peak, specific for the type of surface site, and the corresponding terrace size. The evaluation of the (100) bidimensional domains can also be achieved using the voltammetric profiles, once the fraction of (111) ordered domains present in the polyoriented platinum has been determined and their featureless contribution has been subtracted from the whole voltammetric response. Using that curve, it is possible to perform a deconvolution of the adsorption states of the polycrystalline sample different from those related to (111) domains. The fraction of (100)-related states in the deconvoluted voltammogram can then be compared to that expected from the independent estimation coming from the charge involved in the redox process undergone by the irreversibly-adsorbed germanium and thus check the result of the deconvolution. The information about the surface-site distribution can also be applied to analyze the voltammetric profile of nanocrystalline platinum electrodes.

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Ethanol oxidation has been studied on Pt(111), Pt(100) and Pt(110) electrodes in order to investigate the effect of the surface structure and adsorbing anions using electrochemical and FTIR techniques. The results indicate that the surface structure and anion adsorption affect significantly the reactivity of the electrode. Thus, the main product of the oxidation of ethanol on the Pt(111) electrode is acetic acid, and acetaldehyde is formed as secondary product. Moreover, the amount of CO formed is very small, and probably associated with the defects present on the electrode surface. For that reason, the amount of CO2 is also small. This electrode has the highest catalytic activity for the formation of acetic acid in perchloric acid. However, the formation of acetic acid is inhibited by the presence of specifically adsorbed anions, such as (bi)sulfate or acetate, which is the result of the formation of acetic acid. On the other hand, CO is readily formed at low potentials on the Pt(100) electrode, blocking completely the surface. Between 0.65 and 0.80 V, the CO layer is oxidized and the production of acetaldehyde and acetic acid is detected. The Pt(110) electrode displays the highest catalytic activity for the splitting of the C-C bond. Reactions giving rise to CO formation, from either ethanol or acetaldehyde, occur at high rate at any potential. On the other hand, the oxidation of acetaldehyde to acetic acid has probably the lower reaction rate of the three basal planes.

ABSTRACT.The voltammetric profile of preferentially shaped platinum nanoparticles has been used to analyze of the different sites present on the surface. This analysis has been made, for the first time, in NaOH solutions and revisited in sulfuric and perchloric acid media. The comparison with the voltammetric profiles of the model surfaces, i.e., single crystal electrodes, allows assigning the different signals appearing in the voltammograms of the nanoparticle to specific sites on the surface. A good correlation between the shape of the nanoparticle determined by TEM and the voltammetric profile is obtained. For the nanoparticles characterized in alkaline media, the adsorbed species on the surface has been characterized and three major regions can be identified. Below 0.2 V, the major contribution is due to hydrogen adsorption whereas above 0.6 V, adsorbed OH is the main species on the surface. In between both values, the signals are due to competitive adsorption/desorption process of OH/H. New criteria for determining the active area in NaOH solutions has been proposed. In this medium, the total charge density measured between 0.06 and 0.90V stands for 390 µC cm 2 have been characterized, the behavior of the nanoparticles towards CO oxidation has been analyzed.It has been found that the nanoparticle edges are key sites in the oxidation of CO.