Underpotential deposition (UPD)

The electrochemical oxidation of methanol was investigated by using various ad-layer modified Au(111) electrodes in alkaline media in comparison to Au(111), polycrystalline Pd, and polycrystalline Pt electrodes. Catalytic activity of gold toward methanol oxidation has tended to increase in more alkaline media, as reflected in the oxidation peak in the concentration range of NaOH (0.1-3.0 M) studied here. The oxidation peak potential of methanol shifted to more negative potentials, indicating a pH-dependent surface reaction. Among the electrodes studied, single-crystal gold electrode surfaces modified with Pd and Pt ad-layers displayed the highest catalytic activity for methanol oxidation. Additional shifts of about 350 mV in the oxidation peak potential of methanol was observed for both ad-layer modified electrodes to more negative potentials compared to that of bare electrodes. The Pd and Pt ad-layer modified Au(111) electrode surfaces did not only supply a superior electrical contact, but also accelerated electron transfer, as shown by the increase in peak current and the positive shift in peak potential. This effect was supported by the doublelayer capacitance measurements of bare Au(111) and Pd ad-layer modified singlecrystal electrodes where the potential of zero charge changed from 15 to 5 mV.

Magnesium underpotential deposition on gold electrodes from magnesium nitrate-ammonium nitrate melts has been investigated. Linear sweep voltammetry and potential step were used as electrochemical techniques. Scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) were used for characterization of obtained electrode surfaces. It was observed that reduction processes of nitrate, nitrite and traces of water (when present), in the Mg underpotential range studied, proceeded simultaneously with magnesium underpotential deposition. There was no clear evidence of Mg/Au alloy formation induced by Mg UPD from the melt made from eutectic mixture [Mg(NO 3 ) 2 •6H 2 O + NH 4 NO 3 •XH 2 O]. However, EDS and XRD analysis showed magnesium present in the gold substrate and four different Mg/Au alloys being formed as a result of magnesium underpotential deposition and interdiffusion between Mg deposit and Au substrate from the melt made of a nonaqueous [Mg(NO 3 ) 2 + NH 4 NO 3 ] eutectic mixture at 460 K.

Sin ce 1991, w h en the first lithium -ion batteries w ere com m ercialized (S on y), the interest in these batteries have increased significan tly; they are n ow being used in num erous portable electronic equipm ent. W hen lithium is used as an anode in a cell, a passivating film ( S o lid -electrolyte Interphase -S E I ) form s on the surface o f lithium by reaction w ith the non -aqu eou s ( organic ) electrolyte com ponents. This passivating film perm its the construction o f both primary and secondary lithium c ells usin g cathodes that are therm odynam ically unstable tow ard lithium. H ow ever, at high current d ensities the thickness o f this layer decreases and direct reaction b etw een lithium and cathode material can occur. T his leads to a loss o f capacity w ith cy clin g. The loss o f capacity and dendrite form ation cau sin g short-circuiting are the m ost frequent causes for the failure o f rechargeable lithium cells. L ithium -ion batteries or " rocking-chair " batteries use an intercalation com pound for both the p ositive and the negative electrod es and a non-aqu eou s electrolyte( 1 ). Safety

A novel technique to deposit metals on highly conjugated polyaniline films has been developed. In general, electrodeposition of metals, having low reduction potential, from aqueous solution, is difficult due to disruptive effect of hydrogen which evolves during the process. This difficulty is avoided using conducting polymers films with high surface mass density. The polymer chains of these films possess a high degree of conjugation. Such a polymer produces highly stable polarons and therefore has the ability to perform underpotential deposition. Our method involves reduction of polyaniline film with formic acid followed by dipping the coated electrode in the metal salt solution. Deposition of the metal is monitored by rise in the open circuit potential of the electrode. Deposition of metals with high surface mass density has been achieved. The metal is most likely present in the polymer as a coordination complex with amine nitrogen. Such form of metal is expected to have higher cat...

An overview is given of selected theoretical, experimental and computer simulation research on thermodynamic modeling applied to the metal underpotential deposition. Focus is made mainly on the last 20 years. The updtheory on planar surfaces is revisited and the thermodynamic framework is extended to consider underpotential deposition on nanoparticles and to include anion coadsorption, solvation and double layer charging. Results from molecular dynamics and Monte Carlo simulations are shown for systems of experimental interest. At the end some perspectives for further advanced modeling of the present problem are given.

Cd UPD on selenium was studied for an Au-EQCN modified electrode with Se thin-films previously deposited in acid media. The relationship between AFM, cyclic voltammetry and EQCN data provided an analysis of Cd UPD on a semiconductive layer. EQCN measurements demonstrated that the increase of mass during the potentiostatic deposition in UPD conditions was larger than expected for the maximum recovery allowed (i.e. 0.17 ML), which was related to diffusion through the Se thin-film. From AFM data it was possible to normalize voltammetric and gravimetric data, and our results were consistent with a controlled electrodeposition of CdSe structures. The result of the Cd UPD process was a controlled amount of CdSe. In addition, these findings also demonstrated that electrodeposition in UPD conditions can be used as a helpful technique in order to improve control in surface engineering.

Interfacial phenomena involved in the underpotential deposition of tellurium layers were studied with an electrochemical quartz crystal nanobalance (EQCN) in perchloric acid solution (pH = 1). The in situ study of the oxidation kinetics showed that the oxidation of the Te layer deposited neighbor a Te ads /Au provides evidence of TeO 2ads formation with the incorporation of oxygen to induce the formation of H 2 TeO 3 . From the calculations of the first tellurium layer (82 ng cm -2 ), the mass expected for the second layer deposited in underpotential control was found. Moreover, the oxidation of Te ads followed a bi-functional mechanism involving the oxygen incorporated before the tellurium oxidation at high overpotentials. The combination of powerful interfacial methods (cyclic voltammetry and EQCN) gives a new perspective on tellurium electrodeposition and leads to a comprehensive understanding of the interfacial architecture.

The effect of Pb 2+ on polarization behavior of nickel has been investigated in 0.1 M NaClO 4 + 10 À2 M HClO 4 + x M PbO solutions (x = 0, 10 À5 , 10 À4 , 10 À3 ) at room temperature. The cyclic voltammogram has suggested that Pb 2+ degrades the stability of the passive film on Ni. The corrosion potential of Ni shifted to the more noble direction and the anodic current peak of Ni dissolution decreased with increasing Pb 2+ concentration in solution, indicating that Pb 2+ suppresses significantly the anodic dissolution. The underpotential deposition (UPD) of lead on Ni in the potential range more noble than À0.215 V (SHE) corresponding to the equilibrium potential of the Pb 2+ (10 À3 M)/Pb electrode was confirmed by XPS and GDOES analyses. The anodic Tafel slope, b + , of Ni dissolution changed from b + = 40 mV decade À1 in the absence of Pb 2+ to b + = 17 mV decade À1 in the presence of 10 À4 or 10 À3 M Pb 2+ , which was ascribed to the increase in active sites of Ni surface emerged as a result of electrodesorption of Pb adatoms. The roles of Pb adatoms in active dissolution and active/passive transition of Ni were discussed from the above results.

The formation and dissolution of tin ad-layers on polycrystalline platinum were analysed by cyclic voltammetry in aqueous 10 -4 M tin(II)/1 M sulfuric acid in the 0.05-0.70 V versus RHE range. At this concentration level it was possible to observe that platinum sites involving (110) planes are mainly related to tin underpotential deposition. In contrast to previous results, no irreversible adsorption was found in the course of the electrodeposition. Thermodynamic adsorption parameters were calculated from the potential dependence of tin surface coverage. Catalytic properties of this new surface were studied on the basis of oxygen electroreduction as a model. Kinetic runs were performed with rotating ring-disk electrodes on bare and tin-modified platinum surfaces. Molecular oxygen reduction on tin-modified platinum takes place through the production of both water and hydrogen peroxide. This interpretation was confirmed by calculating the reaction order with respect to oxygen.

A simple and readily applicable voltammetric approach is described to characterize and measure the site-hopping surface diffusion of underpotential-deposited (UPD) metal adatoms at nanoelectrodes. UPD refers to the deposition of atoms on foreign metal supports at potentials lower than those predicted by Nernst law for a bulk deposition. Despite its importance in several fields of catalysis, advanced nanofabrication or even atomic nanoengineering by atomic layer epitaxy, diffusion of UPD adatoms is difficult to observe at micro-and macroelectrodes. In fact, at electrodes of usual dimensions, UPD adatoms surface diffusion is masked by other electrochemical phenomena of greater relative amplitudes. Conversely, at nanowires electrodes sealed in glass, only an extremely small fraction of the surface of the wires is exposed to the electrolyte solution and is rapidly loaded. This allows the spillage of UPD adatoms onto the much larger area of the nanowire rod which is immune to Faradaic reactions due to its isolation from the electrochemical solution by the glass casing. Therefore, surprisingly for a UPD process, voltammetric peaks currents and integral desorption charges primarily reflect these diffusional surface processes so that the integral charges vary linearly with the inverse of the square root of the scan rate. This is easily observable and measurable with usual bench-level electrochemical instrumentation. In this work, by using nanoelectrodes with diameters between 90 and 260 nm, we were able to establish the major involvement of this site-hopping surface diffusion of UPD Pb adatoms on polycrystalline gold (Au) and characterize it quantitatively. The equivalent surface diffusion coefficient of UPD Pb adatoms was determined to be ~4.4 × 10 - 11 cm 2 s -1 at room temperature, corresponding to a Gibbs free energy activation barrier of ca. 18.72 kJ mol -1 (i.e., 0.19 eV per Pb adatom) for the reaction of inter-sites exchange of Pb adatoms on a polycrystalline Au surface.

A simple and readily applicable voltammetric approach is described to characterize and measure the site‐hopping surface diffusion of underpotential‐deposited (UPD) metal adatoms at nanoelectrodes. UPD refers to the deposition of atoms on foreign metal supports at potentials lower than those predicted by Nernst law for a bulk deposition. Despite its importance in several fields of catalysis, advanced nanofabrication or even atomic nanoengineering by atomic layer epitaxy, diffusion of UPD adatoms is difficult to observe at micro‐ and macroelectrodes. In fact, at electrodes of usual dimensions, UPD adatoms surface diffusion is masked by other electrochemical phenomena of greater relative amplitudes. Conversely, at nanowires electrodes sealed in glass, only an extremely small fraction of the surface of the wires is exposed to the electrolyte solution and is rapidly loaded. This allows the spillage of UPD adatoms onto the much larger area of the nanowire rod which is immune to Faradaic r...

In situ X-ray diffraction studies of underpotential deposition at the (111) surface of gold are described. By use of a thin film electrode grown on an X-ray transparent substrate, it has been possible to simultaneously vary the potential of the working electrode and collect X-ray diffraction patterns. The distance between the gold surface atoms and the adsorbed atoms is determined by quantitative analysis of the lineshape of the ( ) reflection. It is found that the distance between lead and gold depends on the potential applied, while that of thallium on gold remains constant, in the underpotential region. The cause of this behavior is not known but may be due to the difference of valence between the two species.

ChemInform Abstract Die Reaktionen des Redox-Paares Ru(NH3) ä+'3+, die über einen Aussensph ärenmechanismus verlaufen, werden an Pbad/Pt-, Tlad/Pt-und Tiad/Au-Elektroden sowie an reinen Pt-und Au-Elektroden untersucht. Die Austauschstromdichten bleiben onstant, was die Annahme best ätigt, dass die Reaktion adiabatisch verl äuft, und dass die elektronischen Eigenschaften des Elektrodenmaterials die Geschwindigkeit des Elektronen übergangs nicht beeinflussen. Im Gegensatz hierzu werden Innensph ärenreaktionen durch adsorbierte Metallatome stark beeinflusst (Voltammetrie).

In the fabrication process of microelectronic devices, electrochemical deposition is a widely used and well-established method. For performing the damascene electroplating of copper, deposition additives were usually required, not only to facilitate a void-free filling, but also to obtain superfilling of trenches and vias with high aspect ratios . In the literature, many studies had performed to study the effects of the additives on the growth behavior of copper in the electroplating process. These studies had shown that the bottom-up copper filling of microvias is achieved in the presence of two plating additives at least. The first one was termed as the accelerator which promotes the Cu deposition rate, and the other decreases the deposition rate, referred as the suppressor. In the literature, 3-Mercapto-1-propanesulfonic acid sodium salt (MPS) and Bis-(Sodium Sulfopropyl) -Disulfide (SPS) were the most commonly used

Electrochemical scanning tunneling microscopy (EC-STM) and electrochemical quartz crystal microbalance (E-QCM) techniques in combination with DFT calculations have been applied to reveal the static phase and the phase transition of copper underpotential deposition (UPD) on a gold electrode surface. EC-STM demonstrated, for the first time, the direct visualization of the disintegration of (√3 × √3)R30°copper UPD adlayer with coadsorbed SO 4 2-while changing sample potential (E S ) toward the redox Pa2/Pc2 peaks, which are associated with the phase transition between the Cu UPD (√3 × √3)R30°phase II and disordered randomly adsorbed phase III. DFT calculations show that SO 4 2-binds via three oxygens to the bridge sites of the copper with sulfate being located directly above the copper vacancy in the (√3 × √3)R30°adlayer, whereas the remaining oxygen of the sulfate points away from the surface. E-QCM measurement of the change of the electric charge due to Cu UPD Faradaic processes, the change of the interfacial mass due to the adsorption and desorption of Cu(II) and SO 4 2-, and the formation and stripping of UPD copper on the gold surface provide complementary information that validates the EC-STM and DFT results. This work demonstrated the advantage of using complementary in situ experimental techniques (E-QCM and EC-STM) combined with simulations to obtain an accurate and complete picture of the dynamic interfacial adsorption and UPD processes at the electrode/electrolyte interface.

Electrocatalytic reduction of oxygen at electrochemically deposited Pt ad-layer modified Au(111) electrodes was studied in an O 2-saturated NaOH (0.1 M) solution. The results were compared with those obtained by using a polycrystalline Pt electrode and another Pt-deposited electrode prepared by replacement with Cu on bare Au(111). Linear sweep voltammetry displayed a positive shift of the oxygen reduction potential by about 0.14 V compared to the bare Au(111) electrode. This shift was about 0.06 V compared to a Pt disk electrode. Tafel slopes gradually changed between 0.06 and 0.1 V/dec, from 0.075 to-0.10 V/dec, from lower to higher current density region. The Pt ad-layer clearly served as a catalyst for oxygen reduction via 4-electron transfer. In terms of the desired shift in reduction potential and increased current density, the best electrocatalytic activity was obtained with a 30-s electrodeposited Pt ad-layer modified Au(111) electrode.

Resumen. La seda del hilo de seguridad de araña es un material muy atractivo por sus excelentes propiedades mecánicas, por producirse de forma respetuosa con el medio ambiente y por ser biodegradable. Este material presenta una propiedad singular conocida como supercontracción: si se toma una fibra de seda obtenida por hilado forzado y se sumerge en agua permitiendo libremente el acercamiento de sus extremos, se produce un acortamiento de la longitud de la fibra hasta un 50%. Aún sin llegar a la inmersión en agua, el aumento de la humedad ambiental en un cierto intervalo también induce una fuerza de contracción. En este trabajo se estudia esta fuerza y su evolución en el tiempo para diversos valores de humedad relativa. La especie de araña empleada es Argiope trifasciata.

The tensile properties of the viscid silk of the spider Argiope trifasciata have been characterized. The tensile behaviour of viscid silk and the other constituent of the web, drag line silk, have been compared. All fibers have been retrieved from a single web, and characterized from tensile tests. The morphology of the fibers has been analysed from scanning electron microscope micrographs. Measured cross sectional areas have been used to re-scale force into stress. The viscid silk presents an elastomeric behaviour, although its tensile strength exceeds that of artificial fibers.

En el presente trabajo se estudia la influencia de la radiación UV sobre las propiedades mecánicas y las superficies de fractura de un polímero artificial bioinspirado en la seda de araña. Las fibras de seda de araña constituyen un material enormemente atractivo ya que su elevada resistencia y deformabilidad lo convierten en el material con mayor trabajo hasta rotura de los conocidos hasta el momento. Además se ha encontrado que posee una elevada biocompatibilidad y un comportamiento biodegradable. Debido a estas ...

Resumen. Se han estudiado las propiedades mecánicas del hilo víscido de la especie Argiope trifasciata, analizando su capacidad de absorción y disipación de la energía mecánica y el efecto del recubrimiento adherente, mediante ensayos de tracción simple hasta rotura y ciclos de carga y descarga. Así mismo, se han dado los primeros pasos en el análisis del estado de deformación y tensional de estos hilos en las telarañas. El estudio de la estuctura del material en estado original y después de eliminar el recubrimiento ...

We report on the electrochemical behavior and shape evolution of Pd nanocubes (Pd NCs) and Pd 3 nanooctahedrons (Pd NOs) with an average size of 9.8 nm and 6.9 nm, respectively, in aqueous alkaline medium in the potential range of the underpotential deposition of H (UPD H) and H 5 absorption. While the Pd NCs and Pd NOs remain stable in the potential region of the UPD H, H 6 absorption and desorption induce structural changes to the Pd NPs, as indicated by the results of 7 electrochemical measurements and identical-location transmission electron microscopy (IL-TEM) 8 analyses. Because both Pd NCs and Pd NOs are known to be stable in the potential region of H 9 absorption and desorption in acidic medium and maintain their structure, the irreversible structural 10 changes are attributed to their interfacial interaction with the aqueous alkaline medium. In the 11 alkaline medium, the nanoparticle surface/electrolyte interfacial structure plays an essential role 12 in the mechanism of H desorption that is observed at higher potentials than in the acidic medium. 13 Hydrogen desorption is substantially hindered due to the structure of water network adjacent to 14 the Pd nanoparticles or the interaction between hydrated cations and adsorbed OH on the 15 nanoparticle surface, resulting in the trapping of a small amount of H (incomplete H desorption). 16 It is proposed that H trapping and associated structural strain lead to deformation of the Pd 17 nanoparticles and loss of their initial structure.

The electrochemical deposition of copper onto Au(100) has been investigated using in situ scanning tunneling microscopy (STM ) and in situ surface X-ray scattering (SXS). Copper deposition from sulfuric acid solutions starts at potentials positive of the reversible Nernst potential, where a pseudomorphic (1×1) copper monolayer forms. Negative of the Nernst potential, STM measurements have revealed that bulk copper nucleates at the surface defects, step edges or island rims of the gold substrate. A bilayer of copper is formed on top of the underlying copper monolayer and further growth proceeds in a layer-by-layer fashion. Atomic resolution STM images have shown that the copper film has a pseudomorphic structure for films less than or equal to 10 layers. Surface X-ray scattering measurements have confirmed the pseudomorphic arrangement and have provided a precise measure of the copper layer spacing (1.45±0.02 A ˚), in good agreement with the value obtained from the copper-copper step height in the STM measurements. This layer spacing is much smaller than the value expected for fcc copper. The combined structural analysis leads to the conclusion of a thermodynamically stable bcc-like structure. Both the X-ray and STM results suggest alloying at the copper-gold interface.

We report on the method for synthesizing palladium nanowires and nanorods involving the electrodeposition on oxidized amorphous carbon nanoparticles from chloride containing solutions. The effect of the deposition overpotential and the concentration of palladium ions on the morphology of the Pd electrodeposits have been established. Palladium grows predominately in the shape of nanowires if electrodeposited at potentials in the H underpotential deposition potential (UPD) range, where chloride ions are adsorbed only at the edges of nucleated monolayer-thick clusters on the carbon surface. The effect of the concentration of palladium ions on deposits’ morphology is also discussed. The mechanism of electrodeposition of Pd nanowires and nanorods in the H UPD potential range has been proposed.

Results from electrochemical and in-situ surface X-ray scattering studies of Cu underpotential deposition (upd) on Au(111) and Pt(111) surfaces in the presence of bromide anions are compared. On Au(111) two different ordered structures have been found by GIXD. At the initial stages of Cu deposition, an enhancement of bromide adsorption is observed resulting in the formation of a bromide incommensurate hexagonal structure, which compresses when the potential is scanned in the negative direction. At +0.32 V, there is a phase transition giving rise to the formation of a commensurate (4 × 4) bromide structure. This phase transition coincides with the appearance of a very sharp peak in the voltammetric profile. In this structure, copper adatoms are probably sandwiched between the electrode surface and the bromide adlayer. Unlike Cu upd on Pt(111) electrodes, no ordered CuBr adlayer is observed. The differences in behavior of Cu upd on Au(111) and Pt(111) electrodes is ascribed not to energetic considerations, but rather to geometric constraints imposed by the lattice structure of the metal relative to the deposited adlayer. The stability (to rinsing) and kinetics of the adlayers formed on Pt(111) electrodes in the presence of bromide have also been examined.

Results from electrochemical and in-situ surface X-ray scattering studies of Cu underpotential deposition (upd) on Au(111) and Pt(111) surfaces in the presence of bromide anions are compared. On Au(111) two different ordered structures have been found by GIXD. At the initial stages of Cu deposition, an enhancement of bromide adsorption is observed resulting in the formation of a bromide incommensurate hexagonal structure, which compresses when the potential is scanned in the negative direction. At +0.32 V, there is a phase transition giving rise to the formation of a commensurate (4 × 4) bromide structure. This phase transition coincides with the appearance of a very sharp peak in the voltammetric profile. In this structure, copper adatoms are probably sandwiched between the electrode surface and the bromide adlayer. Unlike Cu upd on Pt(111) electrodes, no ordered CuBr adlayer is observed. The differences in behavior of Cu upd on Au(111) and Pt(111) electrodes is ascribed not to energetic considerations, but rather to geometric constraints imposed by the lattice structure of the metal relative to the deposited adlayer. The stability (to rinsing) and kinetics of the adlayers formed on Pt(111) electrodes in the presence of bromide have also been examined.

The surface structure of polycrystalline rhodium electrodes in contact with aqueous sulfuric acid was modified by chemical etching with hot concentrated acid or by applying fast square waves with an upper potential equal to 1.55 V and a lower potential within the-0.75 V to-0.35 V range. Polycrystalline rhodium and chemical etched electrodes were characterized by voltammetry, Cu underpotential deposition (upd) and X-ray diffraction. For electrofaceted surfaces were used voltammetry, Cu upd and SEM, revealing that two modified rhodium electrodes exhibit similar voltammetric characteristics as those found for Rh(111) and Rh(110) single crystals, and a third surface with an equal distribution of (110) and (111) planes. In addition, the upd of Cu on those surfaces corroborated the existence of those crystallographic planes. SEM micrographs show surface structures with a high density of terraces and steps. A mechanism of faceting is proposed.

Different colloidal synthesis methods of platinum nanoparticles with controlled sizes and shapes that are relevant for electrocatalysis studies are reviewed. Four main methods, i.e., water in oil microemulsion (w/o) method, polyacrylate (PA) method, tetradecyltrimethylammonium bromide (TTAB) method, and ethylene glycol method, are used to synthesize platinum nanoparticles. The PA method allowed us to synthesize reproducibly nanocubes, nanooctahedrons, or nanocuboctahedrons/truncated nanooctahedrons with size between 8 and 10 nm, the TTAB method led to the synthesis of nanocubes of about 10 nm, and the w/o method allowed the synthesis of spherical particles of about 3 nm. All these samples could be cleaned for further electrochemical characterization of their surface structure by hydrogen underpotential deposition and by spontaneous deposition and oxidation of bismuth and germanium, leading to a quantitative determination of the (100) and (111) surface domains. The samples prepared by the ethylene glycol method, in the presence or not of polyvinylpyrrolydone as surfactant, were size or shape controlled, but did not allow the electrochemical characterization of their surface due to remaining of strongly adsorbed organic species even after cleaning steps.

We report a study of the underpotential deposition (UPD) of Te monolayers onto Au electrodes from perchloric acid solution using electrochemical quartz microgravimetry (EQCM) and chronocoulometry. We find that tellurium(IV) oxide (as TeO 3 2-, TeO 2 or HTeO 2 +) is adsorbed onto Au at potentials positive of the UPD region. EQCM experiments, in which an Au electrode poised at +0.7 V in pure HClO 4 electrolyte was monitored as a function of time before and after the addition of TeO 2 , showed a slow adsorption of a submonolayer of TeO 2. Energy-dispersive X-ray (EDX) measurements confirm the presence of a Te-containing species on the surface. Two distinct reductive UPD features at approximately +0.400 V and-0.100 V vs Ag|AgCl were observed by cyclic voltammetry. EQCM measurements indicate that there is a small, reproducible mass decrease accompanying the first UPD wave, consistent with the loss of H 2 O from the surface as an adsorbed layer of HTeO 2 + is reduced to a submonolayer of Te atoms. Chronocoulometry indicates a charge density of 160 µC/cm 2 for the first UPD wave, which, when taken together with the mass change data, is consistent with the four-electron reduction of adsorbed HTeO 2 + to Te. In addition, analysis of the currenttime data indicates that this process occurs by a two-dimensional instantaneous nucleation and growth mechanism, resulting in an ordered overlayer with a fractional coverage of ca. 0.41. The second UPD peak results in the formation of a dense monolayer by reduction of HTeO 2 + from solution. This process also appears to occur by a direct four-electron reduction and exhibits simple Langmuir adsorption behavior as evidenced by exponentially decaying current-time transients. The saturation coverage is approximately 0.9.

A novel technique to deposit metals on highly conjugated polyaniline films has been developed. In general, electrodeposition of metals, having low reduction potential, from aqueous solution, is difficult due to disruptive effect of hydrogen which evolves during the process. This difficulty is avoided using conducting polymers films with high surface mass density. The polymer chains of these films possess a high degree of conjugation. Such a polymer produces highly stable polarons and therefore has the ability to perform underpotential deposition. Our method involves reduction of polyaniline film with formic acid followed by dipping the coated electrode in the metal salt solution. Deposition of the metal is monitored by rise in the open circuit potential of the electrode. Deposition of metals with high surface mass density has been achieved. The metal is most likely present in the polymer as a coordination complex with amine nitrogen. Such form of metal is expected to have higher catalytic activity than the zero-valent metal. We have been able to deposit metals such as Mn and Cu. Among these, Mn cannot be deposited on polymer by any other method.

Underpotential deposition (UPD) of cadmium on 15 nm gold nanoparticles stabilized by 1‐mercapto‐undecane‐11‐tetra(ethylene glycol) has been studied by cyclic voltammetry (CV). Particles are adsorbed to a hanging mercury drop electrode (HMDE). It is shown that single cadmium atoms are deposited onto the same surface sites that are active for adsorptive hydrogen reduction when cadmium is absent. Depending on the solution pH, the deposition of cadmium atoms either blocks hydrogen reduction or vice versa, depending on which process occurs first during the cathodic potential sweep. Another remarkable finding is that single cadmium atoms UPD‐deposited are also active for adsorptive hydrogen reduction. The use of CV to interrogate surface protected nanoparticles adsorbed on a HMDE represents a powerful method to study the electrocatalytic activity.

This study presents a novel method for the synthesis of self-assembled cationic surfactants covering gold nanoparticle thin films and determines the underpotential deposition behavior of copper on such films. Based upon the solid-liquid interface penetration of copper ions through a self-assembled molecular layer, the variations in oxidation-reduction potential and the amount of copper ion desorption are determined, using cyclic voltammetry and linear sweep voltammetry analysis. The influence of various capping agents, cetyltrimethylammonium fluoride (CTAF), cetyltrimethylammonium chloride (CTAC), and cetyltrimethylammonium bromide (CTAB), on gold substrates is also determined. The blocking capabilities of surfactants that hinder ion penetration from the solution to the Au surface, through bilayers, are in the order: CTAB C CTAC [ CTAF.

The electrodeposition of Cu-Al alloys, as well as the underpotential deposition (UPD) of A1 onto C u(l 11), were investigated in acidic aluminum chloride/1-methy 1-3-ethylimidazolium chloride ambient temperature molten salt. It was shown that it is possible to produce Cu-Al alloy deposits at potentials positive of that corresponding to the electrodeposition of bulk Al. The onset of Al codeposition was found to occur at approximately 0.30 V versus the A1(III)/A1 couple, and the Cu-Al alloy composition was found to be independent of the Cu(I) concentration, reaching a maximum value of 43 % atomic fraction Al at 0 V. Alloy deposition potentials based on free energy calculations are in good agreement with those observed experimentally for Zn-Al, Cu-Al, CoAl , and Fe-Al deposited at room temperature and Ni-Al deposited at 150 °C from an aluminum chloride/sodium chloride melt. Cyclic voltammograms recorded on Cu(l 11) clearly indicate that UPD of Al commences at about 0.30 V vs. Al and is characterized by two distinct surface processes. In-situ scanning tunneling microscopy (STM) examination indicates that an ordered ad-layer appears on the C u (ll l) surface at potentials positive of the first UPD wave. A possible model representing this structure corresponds to a layer of tetrachloroaluminate ions, oxidatively adsorbed on the C u (lll) surface, with the face of the tetrahedra adjacent to the copper surface.

En las últimas décadas, ha existido un creciente interés por la fabricación, síntesis y preparación de nanopartículas bimetálicas (compuestas por dos elementos metálicos diferentes). Al combinar dos metales en estos nanomateriales, su desempeño muchas veces supera las propiedades asociadas con sus contrapartes monometálicas, y cambiando sus componentes y morfologías se puede modificar exitosamente su desempeño físico, eléctrico o químico. Ampliando de esta manera su campo de aplicación a áreas tales como administración de fármacos, óptica-electrónica, biosensores, separación química, materiales, biotecnología, nanoactuadores, bioimagen y bioterapia. La versatilidad de poder entender cómo combinar distintos elementos metálicos, en diferentes proporciones, a nivel nanométrico y de forma controlada, constituye un nuevo paradigma en la ingeniería de nanomateriales.

En el presente trabajo se analiza la modificación de la topografía de una púa escarificadora (SAE 1045) inspirada en la cutícula del bicho toro (Diloboderus abderus), con el objetivo de reducir la adherencia del suelo a la misma. Por tal motivo, se reportan los resultados experimentales de diferentes pruebas de campo, que corresponden a púas con distintas distribuciones geométricas de cavidades en su superficie. Asimismo, se investigó la evolución de la mojabilidad con el tiempo de ataque químico, con la finalidad de generar distintas jerarquías de rugosidades, imitando el efecto lotus.The present work analyses the modification of the topography of a plowshare (SAE 1045) inspired in the cuticle of a beetle called Diloboderus abderus, with the objective of reducing soil adhesion. Therefore, experimental results of different field tests corresponding to several plowshares with different geometric distributions of cavities are reported. Also, the evolution of wettability with time of e...

En el presente trabajo se analiza la modificación de la topografía de una púa escarificadora (SAE 1045) inspirada en la cutícula del bicho toro (Diloboderus abderus), que habita en nuestro suelo, con el objeto de reducir la adherencia del suelo. Por tal motivo, se reportan resultados experimentales de pruebas de campo que corresponden a una dada distribución geométrica de cavidades.

The effects of Iadsorption on the electrodeposition (under and overpotential deposition) of Cu on polycrystalline Pd electrodes were studied in dilute perchloric acid solutions at 18°C. It had been found that Cu underpotential deposition on polycrystalline Pd exhibits different potentiodynamic features, which are characteristic of defined crystallographic planes of Pd. However, these features varied when the voltammograms were performed in the presence of strongly adsorbable anions, such as I-. In spite of having found a partial inhibition of the Cu voltammetric features in the presence of I-, we calculated integer numbers in the electron transfer to Cu 2؉ and Iions. The change in the values of Cu massive deposition potential due to the presence of Iwas caused by the appearence of a new electrode, that is, the Cu/CuI/Iinterface.

The underpotential deposition upd of Pb onto Pt 111 in solution containing Br was examined by classical RRD E PtŽ111. Ž. electrochemical methods in combination with in situ surface X-ray scattering measurements. The results show that Pb upd onto Pt 111 in the presence of bromide is a competitive process with the total amount of Pb deposited at underpotential being only ca. 0.51 " 5% ML, Ž. less than the amount needed to form a close-packed monolayer, 0.63 ML 1 ML equals 1 Pb atom per Pt surface atom. Deposition of Pb adatoms is accompanied by desorption of about one-half of the bromide adsorbed on the Pt surface at higher potentials, leaving co-adsorbed bromide both in and on-top-of the adlayer. In the potential region where the ratio of co-adsorbed species is close to one Ž. Ž. Ž. E f 0 V there is the slow formation over a period of ca. 2 h of an ordered surface alloy, which has a p 2 = 2 unit cell. No other ordered structures of Pb are observed in the underpotential region.

The synthesis of core-shell Pt(Cu) and Pt-Ru(Cu) electrocatalysts allows for a reduction in the amount of precious metal and, as was previously shown, a better CO oxidation performance can be achieved when compared to the nanoparticulated Pt and Pt-Ru ones. In this paper, the carbon black used as the support was previously submitted to electrochemical oxidation and characterized by XPS. The new catalysts thus prepared were characterized by HRTEM, FFT, EDX, and electrochemical techniques. Cu nanoparticles were generated by electrodeposition and were further transformed into Pt(Cu) and Pt-Ru(Cu) core-shell nanoparticles by successive galvanic exchange with Pt and spontaneous deposition of Ru species, the smallest ones being 3.3 nm in mean size. The onset potential for CO oxidation was as good as that obtained for the untreated carbon, with CO stripping peak potentials about 0.1 and 0.2 V more negative than those corresponding to Pt/C and Ru-decorated Pt/C, respectively. Carbon oxidation yielded an additional improvement in the catalyst performance, because the ECSA values for hydrogen adsorption/desorption were much higher than those obtained for the non-oxidized carbon. This suggested a higher accessibility of the Pt sites in spite of having the same nanoparticle structure and mean size.

Mechanism of copper underpotential deposition at stepped faces of platinum single crystals Pt(hkl) is studied using cyclic voltammetry, scanning probe microscopy, and quantum-chemical modelling. It is shown that the first stage of UPD is one-dimensional decoration of the (100)-or (110)-orientated steps, then copper monolayer forms at (111)-terraces. The final stage is the secondary step decoration. Quantum-chemical modelling, with the using of long-distance potentials of the Cu-Pt and Cu-Cu pair interactions, allows estimating the energy of copper adsorption at different structure elements of the substrate (steps, kinks, terraces) and revealing the succession of the adatom monolayer formation; it also provides additional information for the identifying of the nature of voltametric peaks for different stages of the copper adsorption-desorption.

A study was made of the et&t of cadmium concentration on the process of copper electrocrystallizatioa from an ethylenediamine electrolyte on the (111) crystallographic plane of a copper single crystal. It was shown that a relation exists between superpolarization and depolarization of deposition of Cu-Cd alloy components, and cadmium underpolential adsorption or underpotential deposition. This relation was also detected bv the influence exerted on the kinetic parameters of the given model of C&Cd alloy nucleation and growth.

Underpotential deposition (UPD) of cadmium on 15 nm gold nanoparticles stabilized by 1‐mercapto‐undecane‐11‐tetra(ethylene glycol) has been studied by cyclic voltammetry (CV). Particles are adsorbed to a hanging mercury drop electrode (HMDE). It is shown that single cadmium atoms are deposited onto the same surface sites that are active for adsorptive hydrogen reduction when cadmium is absent. Depending on the solution pH, the deposition of cadmium atoms either blocks hydrogen reduction or vice versa, depending on which process occurs first during the cathodic potential sweep. Another remarkable finding is that single cadmium atoms UPD‐deposited are also active for adsorptive hydrogen reduction. The use of CV to interrogate surface protected nanoparticles adsorbed on a HMDE represents a powerful method to study the electrocatalytic activity.

The electrodeposition of Te on a single-crystalline Au(111) electrode was studied with 1064-nm-excited SH rotational anisotropy measurements. The SH rotational anisotropy was significantly changed with the first underpotential deposition (upd) of Te, and the bulk Te deposition attenuated the anisotropic character of the overall surface symmetry. The change in the SH rotational anisotropy during the first upd of Te was examined using two different models. The first model considered only the contribution of the Au(111) surface to the SHG response, while the second one took into account the contributions of both the Au(111) substrate and the adsorbed Te layer. In the former case, the change in the SH rotational anisotropy can be explained by considering the quenching of the nonlinear susceptibility of the Au(111) surface. The analysis based on the latter model resulted in a rotation angle of 608 for the adsorbed Te layer against the the Au(111) lattice. This value was not consistent with that expected from the adsorbate structure of the first upd layer of Te, i.e., (3× 3)R30°. Thus, the former model seems to be more appropriate to explain the present results. The SH rotational anisotropy measurement also suggests that the morphology became more isotropic after the bulk Te deposition.