Electrodeposition of Ag and Pd on a reconstructed Au(1 1 1) electrode surface studied by in situ scanning tunneling microscopy

Electrochemical deposition of Ag and potential-induced structural change of the deposited Ag layer on a reconstructed surface of Au(1 1 1) electrode were followed by in situ scanning tunneling microscope (STM). A uniform Ag monolayer was formed on a reconstructed Au(1 1 1) surface in a 50-mM H₂SO₄ solution at +0.3 V (vs. Ag/AgCl) after adding a solution containing Ag₂SO₄ so that the concentration of Ag⁺ in the STM cell became ca. 2 μM. No characteristic height corrugation such as the Au reconstruction was observed on the surface, indicating that the lifting of the substrate Au reconstruction occurred by Ag deposition. The formed Ag monolayer was converted to a net-like shaped Ag nano-pattern of biatomic height when the potential was stepped from +0.3 to −0.2 V in the solution containing 2 μM Ag⁺. This result indicates that the substrate Au(1 1 1)-(1 × 1) surface was converted to the reconstructed surface even in the presence of Ag adlayer. Quite different structure was observed for Pd deposition on a reconstructed surface of Au(1 1 1) electrode at +0.3 V and the origin for this difference between Ag and Pd deposition is discussed.     

Oxygen electroreduction on Ag(1 1 1): The pH effect

The rotating ring disk method (RRDE) is applied to investigate the pH effect on oxygen reduction reaction (ORR) on Ag(1 1 1) single crystal surface in 0.1 M KOH and 0.1 M HClO₄. In 0.1 M KOH, the ORR proceeds through 4e⁻ reaction pathway with a very small (0.5-2.5%) peroxide formation in the entire potential range. In 0.1 M HClO₄ the onset potential for the ORR is shifted for ca. 400 mV toward the higher overpotentials compared to the 0.1 M KOH solution. At the low overpotentials, in 0.1 M HClO₄ the ORR proceeds entirely as a 2e⁻ process, i.e, 100% H₂O₂ formation. At higher overpotentials, the initial mixed a 2e⁻ and 4e⁻ reduction is followed by the potential region where the ORR proceeds entirely as a 4e⁻ process, with H₂O formation as a final product. The pH dependent shift in the onset of the ORR as well as the reaction pathway has been explained based on both: a thermodynamic analysis of pH independent rate determining step, and on the pH dependent change in availability of surface active sites and adsorption energies of molecular oxygen and reaction intermediates.     

Adenine adsorption on Au(1 1 1) and Au(1 0 0) electrodes: Characterisation, surface reconstruction effects and thermodynamic study

Adsorption of adenine on Au(1 1 1) and Au(1 0 0) electrodes is studied by cyclic voltammetry, impedance and chronoamperometric measurements in 0.1 M and 0.01 M KClO₄ and in 0.5 M NaF solutions. The experiments performed with flame-annealed electrodes at different contact potentials, scan potential limits and scan rates, suggest different adsorption behaviour on the unreconstructed and reconstructed surface domains. This is confirmed by comparing the results obtained with electrochemically annealed unreconstructed and with flame-annealed reconstructed surfaces. In both cases the initial electrode surface state is characterised by the E_pzc values. The adsorption on reconstructed surfaces takes place at more positive potentials than on the unreconstructed surfaces and induces the lifting of the reconstruction.The thermodynamic analysis is performed on the chronoamperometric data for adenine desorption on well characterised unreconstructed Au(1 1 1) surfaces. To this end a new methodology of the chronoamperometric experiments is introduced. Quantitative thermodynamic adsorption parameters such as surface tension, Gibbs surface excess, Gibbs energy of adsorption, potential versus Gibbs excess slope and electrosorption valency are determined. Weak chemisorption of adenine is inferred with a molecular orientation independent on the coverage and on the electrode potential. It is proposed that adsorbed adenine molecules adopt a tilted orientation at the surface to facilitate the coordination to the gold atoms.     

Kinetic study of nitrate reduction on Pt(1 1 0) electrode in perchloric acid solution

The kinetics of electrocatalytic reduction of nitrate on Pt(1 1 0) in perchloric acid was studied with cyclic voltammetry at a very low sweep rate of 1 mV s⁻¹, where pseudo-steady state condition was assumed to be achieved at each electrode potential. Stationary current-potential curves in perchloric acid in the absence of nitrate showed two peaks at 0.13 V and 0.23 V (RHE) in the so-called adsorbed hydrogen region. The nitrate reduction proceeded in the potential region of the latter peak in the pH range studied. The reaction orders with respect to NO₃⁻ and H⁺ were observed to be close to 0 and 1, respectively. The former value means that the adsorbed NO₃⁻ at a saturated coverage is one of the reactants in the rate-determining step (rds). The latter value means that hydrogen species is also a reactant above or on the rds. The Tafel slope of nitrate reduction was −66 mV per decade, which is taken to be approximately −59 mV per decade, indicating that the rds is a pure chemical reaction following electron transfer. We discuss two possible reaction schemes including bimolecular and monomolecular reactions in the rds to explain the kinetics and suggest that the reactants in the rds are adsorbed hydrogen and adsorbed NO₃⁻ with the assistance of the results in our recent report for nitrate reduction on Pt(S)[n(1 1 1) × (1 1 1)] electrodes: the nitrate reduction mechanism can be classified within the framework of the Langmuir-Hinshelwood mechanism.     

Electroreduction of nitrate ions on Pt(1 1 1) electrodes modified by copper adatoms

Kinetics and mechanism of nitrate ion reduction on Pt(1 1 1) and Cu-modified Pt(1 1 1) electrodes have been studied by means of cyclic voltammetry, potentiostatic current transient technique and in situ FTIRS in solutions of perchloric and sulphuric acids to elucidate the role of the background anion. Modification of platinum surface with copper adatoms or small amount of 3D-Cu crystallites was performed using potential cycling between 0.05 and 0.3 V in solutions with low concentration of copper ions, this allowed us to vary coverage θ_Cu smoothly. Following desorption of copper during the potential sweep from 0.3 to 1.0 V allowed us to estimate actual coverage of Pt surface with Cu adatoms. Another manner of the modification was also applied: copper was electrochemically deposited at several constant potentials in solutions containing 10⁻⁵ or 10⁻⁴ M Cu²⁺ and 5 mM NaNO₃ with registration of current transients of copper deposition and nitrate reduction.It has been found that nitrate reduction at the Pt(1 1 1) surface modified by copper adatoms in sulphuric acid solutions is hindered as compared to pure platinum due to induced sulphate adsorption at E < 0.3 V. Sulphate blocks the adsorption sites on the platinum surface and/or islands of epitaxial Cu(1 × 1) monolayer thus hindering the adsorption of nitrate anions and their reduction. The extent of inhibition weakly depends on the copper adatom coverage. Deposition of a small amount of bulk copper does not affect noticeably the rate of nitrate reduction.Nitrate reduction on copper-modified Pt(1 1 1) electrodes in perchloric acid solutions occurs much faster as compared to pure platinum. The steady-state currents are higher by 4 and 2 orders of magnitude at the potentials of 0.12 and 0.3 V, respectively. The catalytic effect of copper adatoms is largely caused by the facilitation of nitrate adsorption on the platinum surface near Cu_ad and/or on the islands of the Cu(1 × 1) monolayer (induced nitrate adsorption).Hydrogen adatoms block the adsorption sites on platinum for NO₃⁻ anion adsorption and inhibit reactions of nitrate reduction even at moderate surface coverage.The products of nitrate reduction in sulphuric and perchloric acids are essentially the same (NO and ammonia) irrespective of the presence or absence of Cu on the platinum surface.     

Adsorption of phosphate species on poly-oriented Pt and Pt(1 1 1) electrodes over a wide range of pH

The adsorption of phosphate anions from phosphate solutions at poly-oriented and single-crystal platinum electrodes, primarily Pt(1 1 1), was studied over a wide range of pH by cyclic voltammetry. The features observed at the poly-oriented Pt electrode in phosphate solution may be related to the different crystalline facets, the (1 1 1) orientation presenting the most significant behavior in terms of phosphate adsorption. On the reversible hydrogen electrode (RHE) scale, the phosphate adsorption strength decreases with increasing alkalinity of the solution. Qualitatively, three different pH regions can be distinguished. At pH < 6 only a broad reversible peak is observed, corresponding to the adsorption of H₂PO₄⁻ and further deprotonation to adsorbed HPO₄⁻. For 6 < pH < 11 a butterfly feature followed by one or two anodic peaks (depending on scan rate) is observed, ascribed to the adsorption of HPO₄⁻ followed by its subsequent deprotonation to adsorbed PO₄³⁻. The splitting into two or three voltammetric features, and the irreversibility of the two features at more positive potential, is ascribed to the deprotonation reaction leading to a surface species (i.e. phosphate) which needs to change its surface coordination. At pH > 11 a reversible pre-wave and a sharp spike are observed, ascribed to the co-adsorption of phosphate and hydroxide.     

Alloy formation during the electrochemical growth of a Ag-Cd ultrathin film on Au(1 1 1)

The electrodeposition of a Ag/Cd ultrathin film on a Au(1 1 1) surface and the formation of a surface alloy during this process have been studied using classical electrochemical techniques and in situ Scanning Tunneling Microscopy (STM). The films were obtained from separate electrolytes containing Ag⁺ or Cd²⁺ ions and from a multicomponent solution containing both ions. First, the polarization conditions were adjusted in order to form a Ag film by overpotential deposition. Afterwards, a Cd monolayer was formed onto this Au(1 1 1)/Ag modified surface by underpotential deposition. The voltammetric behavior of the Cd UPD and the in situ STM images indicated that the ultrathin Ag films were uniformly deposited and epitaxially oriented with respect to the Au(1 1 1) surface. Long time polarization experiments showed that a significant Ag-Cd surface alloying accompanied the formation of the Cd monolayer on the Au(1 1 1)/Ag modified surface, independent of the Ag film thickness. In the case of an extremely thin Ag layer (1 Ag ML) the STM images and long time polarization experiments revealed a solid state diffusion process of Cd, Ag, and Au atoms which can be responsible for the formation of different Ag-Cd or Au-Ag-Cd alloy phases.     

Thermodynamic approach to the double layer capacity of a Pt(1 1 1) electrode in perchloric acid solutions

A thermodynamic method based on the work done by Frumkin and Petrii [A.N. Frumkin, O.A. Petrii, Electrochim. Acta 20 (1975) 347], to calculate the so-called double layer capacity for a Pt(1 1 1) electrode is proposed. The analysis requires careful measurement of the total charge density versus potential curves for a series of solutions with composition (0.1 − x) M KClO₄ + x M HClO₄. A method in which the total charge densities are determined by integration of cyclic voltammograms recorded in solutions with or without chloride is described. Following this procedure the double layer capacity curves were calculated. The double layer capacity curves displayed three peaks that were tentatively assigned to the solvent reorientation, onset of OH adsorption and completion of the OH adlayer. In the hydrogen adsorption region, the double layer capacity values were 14 ± 5 μF/cm², in good agreement with previous estimates reported in the literature by using other approaches.     

Adsorption of camphor and 2,2′-bipyridine on Bi(1 1 1) electrode surface

Impedance spectroscopy and in situ STM methods have been used for investigation of the camphor and 2,2′-bipyridine (2,2′-BP) adsorption at the electrochemically polished Bi(1 1 1) electrode from weakly acidified Na₂SO₄ supporting electrolyte solution. The influence of electrode potential on the adsorption kinetics of camphor and 2,2′-BP on Bi(1 1 1) has been demonstrated. In the region of maximal adsorption, i.e. capacitance pit in the differential capacitance versus electrode potential curve, the heterogeneous adsorption and diffusion steps are the rate determining stages for camphor and 2,2′-BP adsorption at the Bi(1 1 1) electrode. It was found that for camphor | Bi(1 1 1) interface the stable adsorbate adlayer detectable by using the in situ STM method has been observed only at the positively charged electrode surface, where the weak co-adsorption of SO₄²⁻ anions and camphor molecules is possible. At the weakly negatively charged Bi(1 1 1) electrode surface there are only physically adsorbed camphor molecules forming the compact adsorption layer. The in situ STM data in a good agreement with impedance data indicate that a very well detectable 2,2′-BP adsorption layer is formed at Bi(1 1 1) electrode in the wide region of charge densities around the zero charge potential.     

Vibrational Stark tuning rates from periodic DFT calculations: CO/Pt(1 1 1)

DFT periodic calculations have been used to study the influence of an external electric field on the adsorption of CO on Pt(1 1 1). Particular attention has been focused on the determination of the CO and metal-CO vibrational Stark tuning rates. Stark tuning rates have been calculated at various CO coverages; a linear dependence between the CO Stark tuning rate and the CO surface coverage has been found. We have calculated a value of 68.94 cm⁻¹/(V/Å) for the zero-coverage limit CO Stark tuning rate, in good agreement with the experimental value of 75 ± 9 cm⁻¹/(V/Å). Like the CO Stark tuning rate, the metal-CO vibrational Stark tuning rate also increases as CO surface coverage decreases. In addition, we have found (at 0.25 ML) that the CO Stark tuning rate is similar at different adsorption sites, being only slightly larger at high-coordinated sites. CO vibrational Stark tuning rates of 45.58, 47.96, 47.61 and 48.49 cm⁻¹/(V/Å) have been calculated for ontop, bridge, hcp and fcc hollow sites, respectively. Calculations at high coverage using a (2 × 2)-3CO model yield a CO Stark tuning rate of 21.08 and 25.93 cm⁻¹/(V/Å) for ontop and three-fold hollow CO, respectively. These results show that the CO Stark tuning rate for CO adsorbed at high coordinated sites is only slightly larger than that at ontop sites. This result is in contradiction with experiments, which reported larger CO Stark tuning rates at high-coordinates sites than at ontop sites. Furthermore, the calculated metal-CO stretch is larger for ontop sites than for high-coordinated sites; this result is in disagreement with previous DFT cluster model calculations. Unfortunately, there is not experimental information available to support either result. Finally, we have also studied the CO adsorption site preference dependence on electric fields. We have found that CO adsorbs preferentially at high coordinated sites at more negative fields, and at ontop sites at more positive fields, in agreement with previous experiments and DFT cluster model calculations.     

Carboxymethylchitosan + Cu mixture as an inhibitor used for mild steel in 1 M HCl

The inhibition effect of Carboxymethylchitosan (CMCT), Cu²⁺, and CMCT + Cu²⁺ mixture on the corrosion of mild steel in 1 M HCl has been investigated using gravimetric and electrochemical techniques. CMCT + Cu²⁺ mixture acts much more effectively than the inhibiting action of each additive separately. In addition, higher efficiency is achieved for the mixture of 20 mg L⁻¹ CMCT + 10⁻⁴ M Cu²⁺. The efficiency of the optimal mixture increases with the temperature in the range 298-353 K. Activation energy of corrosion reaction in the presence of the optimal mixture of the inhibitors is much lower than that exhibited in 1 M HCl solution. The inhibition mechanism proposed in this paper is based on the results of conductometric investigations.     

Electron-transfer characteristics of ferrocene attached to single-walled carbon nanotubes (SWCNT) arrays directly anchored to silicon(1 0 0)

High-density, surface-mounted ferrocene has been prepared using covalent immobilisation of an alcohol substituted ferrocene derivative to a pre-assembled single-walled carbon nanotubes directly anchored to silicon(1 0 0) surface (SWCNTs-Si). The formation of these ferrocene-modified electrodes (Fc-SWCNTs-Si) has been followed using X-ray photoelectron spectroscopy and atomic force microscopy. Electrochemical results show the surface concentration of ferrocenemethanol molecules is 9.26 × 10⁻⁸ mol cm⁻², which is about 500-1000 times greater than the experimentally measured coverage of ferrocene directly attached to flat Si(1 0 0) surfaces. The reversible one-electron wave of the ferrocene/ferrocenium couple was observed at 490 mV versus Ag⁺/Ag and the apparent rate constant of electron transfer, k_app, was 21 s⁻¹. These results suggest these ferrocene-modified electrodes are excellent candidates for molecular memory devices.     

In situ radiotracer and voltammetric study of the formation of surface adlayers in the course of Cr(VI) reduction on polycrystalline and (1 1 1) oriented platinum

This paper is focused on the in situ radiotracer and voltammetric studies of the induced HSO₄⁻/SO₄²⁻ adsorption at Pt(poly) and Pt(1 1 1) surfaces in 0.1 mol dm⁻³ HClO₄ solution in the course of Cr(VI) electroreduction. Besides this, the sorption behavior of HSO₄⁻/SO₄²⁻ ions on bare Pt(poly) and Pt(1 1 1) electrodes is compared and discussed. From the experimental results it can be stated that: (i) although the extent of bisulfate/sulfate adsorption is strongly dependent upon the crystallographic orientation of Pt surfaces, the maximum coverage on the Pt(1 1 1) does not exceed 0.2 monolayer; (ii) the Cr(VI) electroreduction on both poly- and (1 1 1) oriented platinum proceeds via a ce (chemical-electron-transfer) mechanism to yield Pt surfaces covered with intermediate surface adlayers containing Cr(VI) particles (and reduced Cr-containing adspecies) and ‘strongly bonded’ HSO₄⁻/SO₄²⁻ ions; (iii) while the coverage of platinum surfaces by the intermediate complexes formed in the course of Cr(VI) electroreduction at E > 0.20 V is basically independent of the crystallographic orientation of the Pt electrode, the onset for rapid Cr(VI) reduction is highly affected by the nature and crystallographic orientation of the electrode.     

Potential of zero free charge of Pd overlayers on Pt(1 1 1)

Differential capacitance measurements of Pd overlayers on a Pt(1 1 1) electrode in dilute aqueous NaF solutions have been performed as a function of film thickness in order to determine the potential of zero free charge (pzfc). The pzfc of the first, pseudomorphic Pd monolayer on Pt(1 1 1) is −0.21 V versus SCE. By increasing the amount of deposited Pd, a clear shift of the pzfc to more positive values is observed. After deposition of an equivalent of 10 monolayers, the value approaches that of a massive Pd(1 1 1) electrode (−0.12 V versus SCE). The pzfc's for the various Pd coverages are correlated with surface structure information, derived from STM images (R. Hoyer, L.A. Kibler, D.M. Kolb, Electrochim. Acta 49 (2003) 63). Variations in the pzfc are discussed in the context of an electronic modification by the underlying substrate and are compared with corresponding data for Pd overlayers on Au(1 1 1).     

Surface X-ray scattering of high index plane of platinum containing kink atoms in solid-liquid interface: Pt(3 1 0) = 3(1 0 0)-(1 1 0)

Surface structure of Pt(3 1 0) = 3(1 0 0)-(1 1 0), which contains kink atoms in the step, has been determined with the use of in situ surface X-ray scattering (SXS) in the double layer region (0.50 V(RHE)) in 0.1 M HClO₄. Clean Pt(3 1 0) surface has pseudo (1 × 1) structure on which lateral displacements of 2-9% and 0.3-1% are found along a and b directions, respectively, whereas the surfaces of Pt(1 1 0) = 2(1 1 1)-(1 1 1) and Pt(3 1 1) = 2(1 0 0)-(1 1 1) are reconstructed to (1 × 2) according to previous reports. Interlayer spacing between the first and the second layers d₁₂ is contracted about 5% compared with the bulk spacing, whereas those between underlying layers are expanded down to fourth layer. Fully adsorbed CO has no effect on the surface structure of Pt(3 1 0). This result differs from that on Pt(1 1 1), where d₁₂ is expanded after CO adsorption.     

Electrochemical characterization of irreversibly adsorbed germanium on platinum stepped surfaces vicinal to Pt(1 0 0)

The electrochemical behavior of germanium irreversibly adsorbed at stepped surfaces vicinal to the Pt(1 0 0) pole is reported. The process taking part on the (1 0 0) terraces is evaluated from charge density measurements and calibration lines versus the terrace dimension are plotted. On the series Pt(2n − 1,1,1) having (1 1 1) monoatomic steps, the charge involved in the redox process undergone by the irreversibly adsorbed germanium is able to account for (n − 0.5) terrace atoms, thus suggesting some steric difficulties in the growth of the adlayer on the (1 0 0) terraces. Conversely, no steric problems are apparent in the series Pt(n,1,0) in which more open (1 0 0) steps are present on the (1 0 0) terraces. In this latter case the charge density under the germanium redox peaks is proportional to the number of terrace atoms. Some comparison is made with other stepped surfaces to understand the behavior and stability of germanium irreversibly adsorbed on the different platinum surface sites.     

Redox behavior of hemin at p-GaAs(1 0 0) electrode

Electrochemical behavior of hemin on p-GaAs(1 0 0) electrodes was examined by cyclic voltammetry (CV) and impedance spectroscopy (EIS) in phosphate buffer solutions (PBS) at pH 7.45. CV investigations in 0.6 mM hemin in PBS revealed a pair of reversible peaks at −0.44 and −0.32 V vs. SCE resulting in stable adsorbed species. EIS spectra analysis pointed out that these adsorbed species bring significant changes in the semiconductor surface state population and the potential drop distribution between the semiconductor space charge region and the Helmholtz layer.     

Structure and electrochemical characterization of electrolytic Ni + Mo + Si composite coatings in an alkaline solution

Ni + Mo + Si coatings were obtained by nickel deposition from a bath containing suspension of molybdenum and silicon powders. These coatings were obtained in galvanostatic conditions, at the current density of j_dep = −0.100 A cm⁻². For determination of the influence of phase composition and surface morphology of obtained coatings on changes of corrosion resistance, these coatings were modified in argon atmosphere by thermal treatment at the temperature of 1100 °C during 1 h. A scanning electron microscope was used for surface morphology characterization of the coatings. Chemical composition of obtained coatings was determined by X-ray fluorescence spectroscopy method. Phase composition investigations were conducted by X-ray diffraction method. It was found that the obtained coatings are composed of three phase structures, i.e., nickel, molybdenum and silicon. Phase composition for the Ni + Mo + Si coatings after thermal treatment is markedly different. The main peaks corresponding to the Ni and Mo coexist with the new ones corresponding to new phases: Mo₅Si₃, NiSi, Mo₂Ni₃Si and Ni₆Mo₆C_1.06.Electrochemical corrosion resistance investigations were carried out in the 5 M KOH, using potentiodynamic and electrochemical impedance spectroscopy methods. On the basis of these investigations it was found that Ni + Mo + Si coatings after thermal treatment are more resistant in alkaline solution than Ni + Mo + Si as-deposited coatings. The reason of this is presence of silicides in the coatings.     

Electrochemical characterization of kinked Pt(7 5 1) surface in acidic media

Kinked Pt(7 5 1) surface was prepared and its electrochemical behaviors under different pretreatment conditions in acidic media were investigated systematically by using cyclic voltammetry. The results demonstrated that the upper limit of potential scanning and cooling atmospheres after the Pt(7 5 1) having been flame-annealed significantly influence the voltammetric behavior of Pt(7 5 1) electrode. The electric charge of hydrogen adsorption-desorption slightly increases with increasing the upper limit of potential scanning. Different cooling atmospheres give rise impacts to the surface structure of Pt(7 5 1) electrode, but hardly change the amount of hydrogen adsorption-desorption sites on the electrode. In addition, the so-called third oxidation peak appears near −0.08 V in H₂SO₄ media and −0.05 V in HClO₄ solution because of the presence of (1 1 0) terrace sites on this surface, and a plausible mechanism for the formation of this current peak is discussed. The results are of importance in understanding the electroadsorption properties of the kinked Pt(7 5 1) surface, as well as in further exploration of this kinked electrode in electrocatalysis.     

Oxidation of formaldehyde and ethanol on Au(1 1 1) and Au(1 1 1) modified by spontaneously deposited Ru in sulfuric acid solution

The oxidation of formaldehyde and ethanol on both pure Au(1 1 1) and Au(1 1 1) modified by approximately 0.3 monolayer (ML) of spontaneously deposited Ru was studied by cyclic voltammetry (CV) in 0.5 M H₂SO₄ solution containing either 0.25 M formaldehyde or 0.35 M ethanol. In situ scanning tunneling microscopy (STM) and CV were employed to characterize the Au(1 1 1) and Ru/Au(1 1 1) surfaces. The oxidation of HCHO on Ru/Au(1 1 1) commences at 0.1 V more negative potential than on pure Au(1 1 1). From 0.25 to 0.55 V vs. (Ag/AgCl), the reaction occurs with increasing current, showing a peak at a potential of 0.43 V. It is assumed that the increasing anodic activity of the Ru/Au(1 1 1) surface is associated with the oxidation of some reaction intermediates, facilitated by the presence of Ru in its metallic state. On the other hand, the oxidation of ethanol on Ru/Au(1 1 1) commences at 0.1 V more positive potential than on pure Au(1 1 1), and proceeds in the potential region from 0.2 to 0.5 V with significantly smaller currents, showing a peak at 0.43 V. This inhibiting effect is explained by the deactivation of the most active Au(1 1 1) step sites by high coverage with Ru islands. The appearance of a small peak at 0.43 V is most likely associated to the oxidation of some intermediates during ethanol oxidation at the Ru/Au step sites formed on the Au(1 1 1) terraces by the presence of a small coverage with Ru islands.