Bromide adsorption on Pt (111) is investigated by means of cyclic voltammetry and CO displacement experiments at different pH values. In acidic pH bromide adsorption is strongly overlapped with hydrogen desorption process. However, as the pH increases, hydrogen adsorption process displaces towards negative potentials while bromide adsorption remains nearly in the same potential region. In consequence, both processes decouple at higher pH values. The structural transition from Pt(111)-(1×1) to Pt(111)(3×3)-4Br is pH independent, in the SHE scale, and not observed for pH > 9.1. Values of pztc are extracted from the combination of voltammetric and CO displacedcharges. An alternative approach to obtain charge curves is based on the coincidence of the curves the structural transition characteristic of the bromide adlayer completion.Pztc values obtained from different approaches with and without bromide are compared and their dependence on pH discussed. A thermodynamic analysis is carried out to obtain hydrogen Gibbs excess and charge number from the Esin Markov analysis.or "commensurate" depending on what type of interaction is stronger, as pointed out by Lucas et al. 15 On the one hand, if the interaction between nearby adatoms is stronger, the structural adlayer will be "incommensurate". On the other hand, if the adatomsubstrate interaction is stronger, then structural adlayer will be "commensurate".Bromide adsorption on Pt(111) was subject of investigation by Hubbard's group [16][17][18] providing precious information about the characterization of the formed adlayers.UHV measurements by LEED and Auger spectroscopy were employed to characterize the adlayer, and these works opened the way for further similar investigations. 3,19-22 The Pt(111)-Br ads adlayer was also characterized by STM 3,23 and surface X-ray scattering. 19 The bromide adlayers can be formed either from bromide solutions or bromide vapors. 3 A structural transition at 0.25 V vs. RHE in 0.1 M HClO 4 was observed. 3,18,23 It was first proposed that this feature corresponds to the change from a Pt(111)-(3×3)-4Br adlattice at high potentials to a Pt(111)-(4×4)-7Br adlattice at low potentials, 18 but Itaya et al. observed an incommensurate Pt(111)-(1×1) structure instead of Pt(111)-(4×4)-7Br. 23 Independently of the technique used for the characterization of the Pt(111)-Br ads adlayer, it was shown that the Pt(111)-(3×3)-4Br structure is dense and the bromine adatoms are arranged in a closed-packed hexagonal layer, where the Br-Br distance is close to van der Waals diameter of bromine. They pointed out also that these adlayers are ordered preferentially along the directions of the substrate densest rows. 3,[16][17][18]24 Lucas et al. 19 proposed similar observations, although in these studies they observed that the (3×3) adlayer structure was incommensurate, whereas Orts et al. 3 proposed it as commensurate.In the present work, the knowledge about bromide adsorption on Pt(111) is extended by performing cyclic voltammetry and CO displacement experiments...

Stepped Pt surfaces having different width (111) terraces interrupted by (110) or (100) monoatomic steps were employed to evaluate the catalytic activity towards CO oxidation at specific sites of these surfaces in HClO4, H2SO4, and H3PO4 solutions, as well as in phosphate buffer and alkaline solution. The catalytic activity at the (111) terraces was sensitive to the nature of the anions derived from the electrolyte dissociation, while no effect on catalytic activity was detected at the monoatomic steps. For the same stepped surface, a change in solution pH, passing from acid to alkaline solutions, had contrasting effects on catalytic activity at the (111) terraces and the step sites, with the catalytic activity of the (111) terraces improving, while catalytic activity at the step sites deteriorated. It was found that the release of CO surface sites occurred preferentially from the (111) terraces of the Pt(s)-[(n-1)(111)×(110)] series, while from Pt(s)-[(n)(111)×(100)] surfaces, (111) terrace and (100) step sites were released simultaneously.

Oxygen reduction reaction (ORR) is studied on Pt(111) in the presence of different concentrations of bromide anions at different pH values ranging from very acidic to neutral solutions. While adsorbed bromide inhibits the ORR, the strength of the inhibition decreases when the pH is increased. This is a consequence of the lower relative adsorption energy of bromide at higher pH values, caused by the lower absolute applied potential. This is reflected in a shift of the onset of the ORR (as measured with the hanging meniscus rotating disc electrode, HMRDE) to higher values as the pH is increased. HMRDE measurements reveal that the limiting current density (j lim) coincides with the theoretical value for two electrons only at very acidic solutions. However, when pH is increased, j lim tends toward the value for a four electrons reaction. From pH > 3 j lim coincides both in the presence and in the absence of bromide despite the specific anion adsorption. Experiments in solutions with different ionic strength and hydrogen peroxide reduction measurements suggest that the formation of a reaction intermediate different from H 2 O 2 is favored at neutral pH values.

The catalytic effect of Pd on gold electrodes for glycerol oxidation is evaluated for Pd-Au surfaces prepared using three different methods: irreversible adsorption of palladium by a simple immersion of a gold electrode in palladium solution, the deposition of palladium on the gold substrate by a step potential from 1 to 0.75 V, and the forced deposition of palladium on the gold electrode with the help of a reducing hydrogen atmosphere. Voltammetry has been used for the electrochemical characterization of the Pd-Au deposits and to determine its reactivity towards glycerol oxidation, whereas FTIR experiments have allowed detecting adsorbed species and products formed during the oxidation reaction. Pd-Au surfaces prepared by irreversible adsorption are the electrodes that show the highest activity for the glycerol complete oxidation to carbonate, whereas Pd-Au surfaces made by the step potential are the catalyst that exhibits the highest rate for the formation and adsorption CO before carbonate production, poisoning the surface and diminishing their electrocatalytic properties. In addition to carbonate, glycerate, glycolate, and formate are detected as oxidation products. The integrated bands of the spectra are used to give quantitative information for comparing the product distribution of the different Pd-Au deposits prepared.

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In this work we performed electrochemical (cyclic voltammetry and chronoamperommetry) and spectroelectrochemical studies (in situ Fourier transform infrared (FTIR)) in PdRuRh electrodeposits in acidic media in presence of ethylene glycol (0.5, 1.0 and 2.0 mol L -1). The electrochemical results show that the ethylene glycol oxidation is sensitive to the composition of the catalysts, being PdRuRh 74:09:17 the composition which presents the best catalytic activity. Also, conversely to Pt, these surfaces do not present a self-inhibitory effect when the EG concentration is increased. FTIR results indicate a complex reaction mechanism under these conditions, where glycolic acid, oxalic acid, formic acid and CO 2 are detected as electro-oxidation products. The best catalytic activity observed for PdRuRh 74:09:17 can be understood in terms of a higher selectivity towards the production of CO 2 , which is the oxidation pathway that involves the release of the major number of electrons.

a b s t r a c tPreliminary studies on the influence of Platinum-Rhodium electrodeposits upon the rate of acetaldehyde electrooxidation showed that Rhodium plays a dual role during electrooxidation, because it favors the break of C-C bonds whilst prevents the deliverance of oxygen-containing species, thus inhibiting the oxidation steps. Based on these results, in this work Platinum-Ruthenium and Platinum-Ruthenium-Rhodium electrodeposits were prepared and characterized by electrochemical and spectroscopic methods (FTIR in situ). The addition of Ruthenium is justified by its ability to promote a facile oxidation of adsorbed species by activation of water molecules. The results indicate a compromise between the existence of superficial sites able to break carbon chains (provoked by Rhodium) and responsible by the oxidation of adsorbed species (provoked by Ruthenium). Among the atomic compositions investigated, PtRuRh (73:23:04) shows the maximum activity towards acetaldehyde electrooxidation, but the production of acetic acid seems to be the main responsible for this activity.

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