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.

Reactivity towards methanol and formic acid electrooxidation on Pt nanoparticles with well characterised surfaces were studied and compared with the behaviour of single crystal electrodes with basal orientations. Polyoriented and preferential (100), (111) and (100)-(111) Pt nanoparticles were synthesised, cleaned preserving its surface structure, characterised and employed to evaluate the influence of the surface structure/shape of the Pt nanoparticles on these two relevant electrochemical reactions. The results pointed out that, in agreement with fundamental studies with Pt single crystal electrodes, the surface structure of the electrodes plays an important role on the reactivity of both oxidation processes, and thus the electrocatalytic properties strongly depend on the surface structure/shape of the nanoparticles, in particular on the presence of sites with (111) symmetry. These findings open the possibility of designing new and better electrocatalytic materials using decorated shape-controlled Pt nanoparticles as previously described with Pt single crystal electrodes.

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.

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