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We present a comprehensive study on the initial stages of silver electrodeposition on Pt (111), Au (111), and Au (100) single crystal surfaces in low-viscosity ionic liquids (ILs) containing dicyanamide anions: 1-butyl-1-methylpyrrolidinium dicyanamide [BMP][DCA] and 1-butyl-3-methylimidazolium dicyanamide [BMIm][DCA]. Electrochemical methods in combination with in situ scanning tunneling microscopy (STM) and ex situ atomic force microscopy (AFM) are employed to explore the Ag underpotential (upd) and overpotential (opd) deposition processes as well as the stability of the single crystal electrode surfaces in the absence of Ag+ ions. The substrate material is shown to significantly affect the mechanism of Ag deposit nucleation and growth in the ILs. While no Ag upd is detected on Pt (111), the formation of a Ag upd monolayer on a Au (111) electrode in both ILs is clearly visualized by in situ STM. The Ag adlayer formation on the Au electrodes in the underpotential regime facilitates Ag opd, which starts on Au (111) and Au (100) at much less negative potentials than on Pt (111). There is an excellent agreement between the electrochemical (voltammetry and chronoamperometry), AFM and STM data, demonstrating the nucleation and growth of individual Ag crystallites on Pt (111) according to the Volmer–Weber mechanism and the layer–by–layer growth of Ag deposit on Au (111) and Au (100). Only at high overpotentials, the Ag growth on the gold electrodes switches to the Stranski-Krastanov mode involving the appearance of 3D crystallites.

Rare-earth elements (REEs) are one of the most important raw materials and are of vast significance for the modern hi-tech industry. Electrochemical deposition of REE-containing materials can provide a real alternative to currently used high-temperature processes of molten salt electrolysis. Here we study the process of Eu electrodeposition from 1‑butyl‑1-methylpyrrolidinium dicyanamide IL, [BMP][DCA], containing controlled amount of water. The Eu deposition is performed on Pt(111) single crystal as well as on Au(111) and glassy carbon electrodes. We show that addition of water (up to 3.092 M) to a [BMP][DCA] solution promotes the electroreduction of Eu ions to Eu(0) shifting the potential of Eu deposition in the positive direction. The potential shift is already pronounced after addition of a moderate water amount and is equal to ~0.28 V upon increase in cH2O from 0.012 to 0.167 M. Microscopic and X-ray spectroscopic analyses of the electrodes after potentiostatic polarization confirm the formation of Eu deposit, however Eu in the deposit is mainly in the oxidized form. The oxidation of electrochemically deposited Eu(0) can occur simultaneously with the electrodeposition process in the chemical reaction with residual or added water. Furthermore, the electrode material is found to affect the overpotential of Eu deposition, and the deposition accelerates in the order of GC

Nitrate electroreduction is studied on Pt(S)-[n(100)x(110)] stepped platinum single crystals with 2, 4, and 6 atoms wide terraces modified by copper adatoms. The electrodes were modified by electrodeposition of Cuad in a 0.1 M HClO4 + 0.020 M NaNO3 + 10−5 M Cu(ClO4)2 solution by cycling the potential in the range of 50–350 mV, simultaneously with nitrate reduction. The peak of dissolution of copper adatoms in the nitrate solution is shifted in the positive direction, as compared to the nitrate–free solution, due to the stabilization of copper adatoms by adsorbed NO. This shift is not observed for Pt(210) with the terrace width of only 2 atoms: an increase in the terrace width results in the growing peak shift. The rate of nitrate electroreduction on modified electrodes increases by up to two orders of magnitude and grows at low copper coverages at an increase in the terrace width in the sequence of Pt(210)

Neodymium is one of the most important rare earth elements due to its various applications, above all, in permanent magnets in consumer electronics and renewable power sources. Production of primary Nd is a rather complex and expensive process characterized by significant import dependency, which brings to the forefront Nd recovery from secondary sources. Electrowinning as one of the cheapest and processible solutions is not applicable for electropositive rare earths in aqueous systems but is a good option in the case of solutions based on ionic organic solvents. Nd electrodeposition and its induced codeposition with Fe are studied at room temperature in a fluorine-free dicyanamide ionic liquid (IL) using a complex set of electrochemical and physical (spectroscopic and microscopic) methods in dry solutions and in the presence of water. We show that the addition of water significantly promotes electrodeposition of individual metals in the respective single-component solutions but produces a hindering effect on the induced codeposition of Nd with Fe. We suggest an explanation for the acceleration of individual Nd and Fe in the presence of water based on the effects at the IL/electrode interface and for the inhibition of Nd-Fe deposition in the presence of water owing to the decelerating effect of formation of Nd oxide/hydroxide film. This is the first systematic study of the effect of water on the rare earth–transition metal codeposition in ILs providing information that can be essential for production of secondary rare earths and fabrication of novel lanthanide-based materials.

In this work, electroreduction of nitrate anions on bare and copper-modified platinum nanoparticles (Pt NPs) supported on glassy carbon is studied using cyclic voltammetry. Two types of Pt NPs are chosen for this purpose: unshaped (polyoriented) NPs and cubic NPs displaying the preferential (100) orientation of faces. The modification of cubic and polyoriented Pt NPs by copper adatoms with submonolayer coverages is performed in a controlled way in solutions containing small concentrations of Cu 2 + ions, 10 − 5 M. Nitrate reduction is studied first in copper-free solutions and then in the presence of 10 − 5 M Cu 2 + . The transmission electron microscopy and voltammetric measurements of the cubic NPs indicate the presence of a significant amount of Pt(100) terraces on the surface of these NPs. In perchloric acid solutions containing 0.02 M NaNO 3 and 10 − 5 M Cu 2 + , accumulation of copper adatoms on the NPs results in a fast increase in the currents of nitrate electroreduction. These reduction currents on the cubic NPs are up to three times higher than on the polyoriented NPs at Cu coverages of 0.20–0.35. The comparison of the data on Pt NPs with the data for single crystal electrodes with (100) terraces of different width (Pt(610), Pt(210)) shows that the behavior of NPs can be simulated on the basis of the data for single crystal faces with wide (cubic NPs) and narrow (unshaped NPs) (100) terraces. Thus, cubic NPs manifest rather a high electrocatalytic activity in the studied reaction of nitrate anion electroreduction, which is typical for single crystal surfaces with relatively wide Pt(100) terraces. At the same time, in comparison with macro single crystalline electrodes, these NPs are characterized by sufficiently higher stability, larger specific surface area, and flexibility in application.

The initial stages of Cu deposition at low overpotentials have been studied on the Pt(100) and Pt(111) basal faces and stepped surfaces Pt(610), Pt(410) of platinum single crystal electrodes. The process includes formation of a Cuad adlayer, an epitaxial monolayer of a two dimensional phase and three dimensional copper crystallites on the (100) terraces, while on the Pt(111) face the two dimensional Cu layer is absent as in this case 3-fold coordination of deposited Cu atoms probably cannot provide sufficient decrease in surface energy of the system. At high enough cathodic overpotentials, the 3D-phase of copper is formed on the monolayer of copper adatoms Pt(111)-Cuad. The Stranski-Krastanov mechanism of nucleation and growth is realized on all the studied electrodes. Financial support from the Russian Foundation for Basic Research (project no. 14-03-00530), MINECO (CTQ2013-44083-P) and Generalitat Valenciana (PrometeoII/2014/013) (Feder, Spain) is gratefully acknowledged.

Pulsed (square–wave) electrodeposition of platinum nanocrystallites with a high concentration of (100) regions from a H2PtCl6 solution with different background anions is studied. The effect of the background electrolyte is shown, namely, a more perfect cubic faceting of crystallites obtained in the 0.1 M HClO4 solution as compared to 0.5 M H2SO4. A procedure for deposit formation (secondary growth) with intermediate pulsed treatment in acid is suggested that does not involve application of high negative/positive overpotentials (no additional increasing of the mobility of platinum atoms). This allows preserving the crystallite structure and improving the overall deposit structure. In addition to conventional methods of fine surface structure determination on the basis of the hydrogen UPD region in cyclic voltammograms in sulfuric acid and SEM, we propose analysis of the Pt(100) terrace concentration/width based on the characteristic peak of nitrate ion reduction in voltammograms in perchloric acid. Stepped Pt single crystals with (100) terraces of different width are used for comparison. The effect of solution temperature on formation of faceted crystallites is shown and the optimum deposition temperature is determined: the optimum temperature in perchloric acid solution is 40 °C, while an increase in the temperature in sulfuric acid solutions results under the chosen conditions in deposition acceleration and an increase in the amount of surface defects.

Herein, we present a study on the initial stages of chromium electrodeposition on platinum and gold single-crystal surfaces from an ionic liquid containing dicyanamide anions. We employed conventional electrochemical techniques in combination with in situ and ex situ scanning probe microscopy (in situ scanning tunneling microscopy (STM), ex situ atomic force microscopy (AFM)) and ex situ X-ray photoemission spectroscopy (XPS). Cr electrodeposition was carried out from Cr(II) and Cr(III) solutions of low (10 mM) and high (250 mM) Cr concentrations. The microscopic and spectroscopic approaches clearly demonstrate the formation of a Cr deposit, although the voltammetric responses are difficult to interpret. The absence of a pronounced Cr dissolution peak in the backward scan of the cyclic voltammograms and a relatively low amount of Cr deposit (as confirmed by AFM) suggest the passivation of Cr and the substrate during deposition, thus hindering both further deposition of Cr and its anodic dissolution.

Techniques of electrode modification by copper deposits are developed that allow obtaining compact bulk quasi-epitaxial deposits on basal Pt(hkl) single crystal faces. The issues of the deposit roughness and characterization are discussed. Problems of drying and transferring electrodes with copper deposits into other solutions are considered. The obtained deposits are used for CO2 electroreduction in propylene carbonate and acetonitrile solutions of 0.1 M TBAPF6, and the relationship between the electrode surface structure and its electrocatalytic activity in CO2 electroreduction is discussed. We also demonstrate that the restructuring of Cu deposits occurs upon CO2 electroreduction. Complementary reactivity studies are presented for bare Pt(hkl) and Cu(hkl) single crystal electrodes. Cu-modified Pt(hkl) electrodes display the highest activity as compared to bare Pt(hkl) and Cu(hkl). Particularly, the Cu/Pt(110) electrode shows the highest activity among the electrodes under study. Such high activity of Cu/Pt(hkl) electrodes can be explained not only by the increasing actual surface area but also by structural effects, namely by the presence of a large amount of specific defect sites (steps, kinks) on Cu crystallites.

Kinetics and mechanism of nitrate anion reduction on the Pt(100) electrode in perchloric and sulfuric acid solutions are studied. Analysis of the results of electrochemical measurements (combination of potentiostatic treatment and cyclic voltammetry) and the data of in situ IR spectroscopy allow suggesting the following scheme of the nitrate reduction process on Pt(100) differing from that in the literature. If the potential of 0.85 V is chosen as the starting potential for a clean flame-annealed electrode surface and negativegoing (cathodic) potential sweep is applied, then an NO adlayer with the coverage of about 0.5 monolayer is formed on Pt(100) in the nitrate solution already at 0.6 V. The further decrease in the potential results in NO reduction to hydroxylamine or/and ammonia, desorbing products vacate the adsorption sites for nitrate and hydrogen adatoms. At E < 0.1 V, adsorbed hydrogen is mostly present on the surface. During positive-going (anodic) potential sweep, the process of nitrate reduction starts after partial hydrogen desorption, the cathodic peak of nitrate reduction to hydroxylamine or ammonia is observed at 0.32 V on cyclic voltammograms. The process of nitrate anion reduction continues up to 0.7 V; at higher potentials, the surface redox process with participation of hydroxylamine or ammonia (the anodic peak at 0.78 V) and nitrate (the cathodic peak at 0.74 V is due to nitrate reduction to NO on the vacant adsorption sites) occurs.

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 θCu 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 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 Cuad 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.

Technique of modification of basal faces Pt(hkl) by adatoms and epitaxial copper deposits is developed. Analysis of potentiostatic current transients of copper deposition/dissolution and atomic force microscopy showed that the activity of Pt(hkl) faces regarding the processes of copper nucleation and epitaxial growth increases in the sequence of Pt(111) < Pt(110) < Pt(100). The reaction of nitrate anion reduction is sensitive towards the surface structure, not only in the case of platinum, but also in the case of copper deposits (including a monolayer of adatoms). The highest process rate is observed for the Pt(100) electrode modified by a monolayer of adatoms or islands of bulk copper; nitrate reduction at the lowest rate occurs at Pt(111) + Cu electrodes. Structure-sensitive competitive adsorption of background electrolyte and nitrate anions is the factor that largely determines the kinetics of nitrate reduction on different faces of platinum single crystal and copper deposits.

The variation of electrode nature and surface structure (the use of stepped single crystal faces with controlled width of (1 1 1) terraces and monoatomic steps of (1 0 0) or (1 1 0) orientation) allows to determine peculiarities of co-adsorption of acetonitrile molecules, hydrogen adatoms and (bi)sulfate anions. It has been shown that first of all acetonitrile blocks adsorption sites at the steps. Anion adsorption at terraces of stepped platinum surfaces in 0.5 M H2SO4 solution with additions of acetonitrile depends on terrace width and the step orientation. This demonstrates the important role of structural factors in competitive adsorption processes. The decrease in adsorption of hydrogen and anions on narrow terraces is substantially due to the influence of acetonitrile molecules placed at the steps or nearby sites. At E < 1.0 V, electrochemical conversion of acetonitrile has not been detected at single crystal Pt surfaces. However, acetonitrile oxidation might proceed on polycrystalline platinum followed by product desorption. On Au(1 1 1) surface acetonitrile adsorption is considerably weaker than that on platinum electrodes.

The kinetics of formation of copper adlayer, three-dimensional nucleation, and the deposit growth on polycrystalline platinum and glassy carbon in the 0.5 M H2SO4 + 10 mM CuSO4 + (0–2) M acetonitrile (AcN) solutions at the cathodic overvoltages is studied using the methods of cyclic voltammetry and potentiostatic current transients on a ring-disc electrode. At [AcN] = 2 M, the process of formation of copper adatoms on platinum is significantly retarded. In the solutions with high contents of AcN, the processes of Cu+ ion production, the formation of their complexes with acetonitrile, hydrogen evolution, copper nucleation, and the deposit growth proceed in parallel. The contribution of any process to the overall current depends on the amount of adsorbed AcN at the surface of substrate and copper deposit and on the electrode potential. At [AcN] = 2 M, an increase in the cathodic overvoltage to 0.32 V leads to an abnormal increase in the current of Cu+ ion production on platinum, which is caused by insufficiently rapid formation of copper atoms in the reduction of Cu+(AcN)x complexes.

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.

The kinetics of copper underpotential deposition on stepped Pt(hkl) electrodes with controlled width of (111) terraces in acidic solutions of copper sulfate with 0–200 mM of acetonitrile (AcN) has been studied by means of cyclic voltammetry. In the presence of AcN Cu UPD process is hindered both at (100) steps and (111) terraces of Pt(171515) and Pt(755) faces due to blocking of the electrode surface with organic molecules, strongly adsorbed at the steps and nearby ones. The decoration of (110) steps with copper adatoms is slightly accelerated for Pt(775) electrode in the solution with 0.04 mM AcN. Increase in AcN concentration leads to inhibition of the UPD process. The difference in behavior of the stepped platinum electrodes is controlled by competitive adsorption of AcN, (bi)sulfate and Cu atoms at the step sites. AcN adsorption at (100) steps is stronger as compared with (110) ones. Keywords: Copper, Stepped single crystal, Adsorption, Acetonitrile

The initial stages of copper electrocrystallization on polycrystalline platinum in 0.5 M H2SO4 + 10 mM CuSO4 + 0–200 mM acetonitrile (AcN) solutions are studied by the methods of cyclic voltammetry and potentiostatic current transients on a ring-disk electrode. Adsorbed AcN molecules accelerate both the underpotential deposition and the bulk deposition of copper due to the local electrostatic effects on the charged interface. With the increase in the additive concentration in solution, the contribution of the production of copper ions Cu+ is observed to increase due to the formation of Cu(AcN) x + comlexes, particularly, for [AcN] ≥ 4 mM when the concentrations of acetonitrile and copper sulfate become comparable. In the presence of AcN, as well as in the copper sulfate supporting electrolyte, the adatomic layer is formed via the mechanism of the two-dimensional growth of Cu(1 × 1) phase islets.

The kinetics of underpotential deposition, three-dimensional nucleation, and growth of copper deposits at cathodic overpotentials on a Pt(111) electrode in solutions containing 0.5 M H2SO4, 10 mM CuSO4, and 0–200 mM acetonitrile (AcN) is studied by the cyclic voltammetry, potentiostatic current transients, and scanning probe microscopy methods. At low volume concentrations of acetonitrile ([AcN] ≤ 4 mM), adsorbed acetonitrile molecules accelerate the formation of a co-adsorption lattice of copper adatoms with anions due to local electrostatic effects at the charged interface. At higher concentrations, the underpotential deposition process is hampered, but the desorption of copper adatoms occurs at potentials more positive than those at low acetonitrile concentrations. This effect is attributed to a stabilizing action of acetonitrile molecules situated on the layer of copper adatoms and, in part, on platinum. At [AcN] = 0.4–40 mM, adsorbed acetonitrile molecules accelerate the growth of the bulk copper deposit, but the nucleation stage is hindered. The dependence of the copper amount on the deposition potential at [AcN] = 40 mM exhibits a maximum at 0.15–0.17 V. This effect was previously observed in weakly acid solutions (pH 1.7–3.0) containing no acetonitrile. The maximum rate of the deposit growth corresponds to an optimum number of crystallites (which is not too great) and an optimum distance between the growing centers in conditions of mixed kinetics “diffusion + electron transfer.” A substantial number of complexes Cu(I)-AcN forms at high acetonitrile concentrations.

Kinetics and mechanism of underpotential (UPD) and overpotential Cu deposition (OPD) on Pt(1 1 1), Pt(7 7 5) and Au(1 1 1) electrodes in sulfate solutions of different acidities (pH 0.3–3.7) are studied. In weakly acid solutions, the rates of both Cu UPD and OPD processes are higher as compared with acid solution of copper sulfate (pH 0.3) due to the enhanced concentration of active centers (copper oxides Cu xO) for 2-D and 3-D phase transitions and accelerated discharge of copper ions. The maximum rate of ( √ 3 × √ 3) R 30 ◦ formation is observed at

The formation of an adatom layer on polycrystalline platinum and the three-dimensional nucleation of copper in a copper perchlorate solution are studied by cyclic voltammetry at 0.1 V s–1 while varying potential ranges and by recording potentiostatic current transients. About 0.6 monolayers of copper adatoms are deposited when cycling with anodic limit E a = 1.35 V, the process is slower than that in an acid sulfate solution. Decreasing E a accelerates the process (nearly one monolayer forms for E a = 0.80–0.95 V in a cathodic scan) due to an increased number of active centers (metastable copper oxides) and, probably, to a change in the platinum surface microstructure. Oxygen for copper oxides is presumably supplied by water molecules adsorbed on a monolayer of copper adsorbed atoms and by subsurface oxygen (Oss), which appears on the platinum surface after the destruction of complexes Oss–Pt n –ClO4. Both the copper nucleation and the deposit growth accelerate at higher concentrations of copper oxides, which form at low E a. High cathodic overvoltages decrease the number of active crystallization centers due to reduction or removal of copper oxides.

The oxidation of polycrystalline platinum in perchloric acid is studied by cyclic voltammetry at a potential scan rate of 0.1 V s–1 in various potential cycling ranges. The earlier model for the formation of a barrier layer of strong complexes consisting of subsurface oxygen Oss, platinum atoms, and anions adsorbed on the latter is shown to correctly describe experimental results on the platinum oxidation in sulfuric and perchloric acids. The regularities in these acids are on the whole similar. A weaker adsorption of perchlorate anions as compared with bisulfate facilitates chemisorption of oxygen at 0.7–0.85 V and hinders exchange by sites Pt ⇔ O at 0.85–1.35 V. A prolonged potential cycling with a cathodic limit of 0.27 V and low anodic limits leads to the accumulation of surface complexes Oss–Ptn–ClO4, which hinder both the oxygen chemisorption and the exchange Pt ⇔ O below 1 V. At more positive potentials, the complexes are destroyed and oxygen penetrates into subsurface platinum layers.

The oxidation of polycrystalline platinum in 0.5 M H2SO4 is studied by cyclic voltammetry at potential scan rates of 5–500 mV s–1 while varying the potential cycling range. The scheme, which is proposed for explaining the observed acceleration and deceleration of oxygen sorption at 0.75–1.0 V, accounts for the presence of oxygen in the subsurface layers of platinum (Oss) and the formation of a barrier layer comprising complexes Oss–Pt n –SO4. Cycling platinum secures certain steady-state contents of Oss at 0.01–1.35 V. In an anodic scan, Oss accumulates at E > 0.85 V (slow post-electrochemical stage) due to exchange of platinum and oxygen atom sites. In a cathodic scan, the desorption of most oxygen gives way to the adsorption of anions, which prevent residual Oss from appearing on the surface. The residual Oss disappears at E < 0.1 V after a sufficiently complete desorption of anions and the destruction of stable complexes Oss–Pt n –SO4. Varying the potential cyclic limit leads, after a delay, to other steady-state Oss contents.

The formation of a copper adatom layer on polycrystalline platinum in a copper sulfate solution is studied by cyclic voltammetry in different cycling ranges at 0.1 V s–1. The copper adatom deposition kinetics is controlled by the following factors. The substrate's top layer structure during the oxygen exit onto the surface may be unstable at anodic limits Ea = 0.90–1.35 V. The concentration of copper oxides (active centers) may be higher at Ea = 0.8–0.95 V. The balance between different adsorption sites differs in different cycling conditions. Of importance is the number of complexes Oss–Ptn–SO4 and Oss–Ptn–Oc, where Oss is subsurface oxygen and Oc is chemisorbed oxygen.

The hydrogen content in electroplated chromium layers and multilayer nickel–chromium coatings applied by periodic current from sulfate–oxalate baths is discussed. Chromium electroplating at periodic and pulsed currents is found to increase the hydrogen content to 54 cm3 /g as compared with 24 cm3 /g for chromium deposits obtained in a direct-current mode. The hydrogen content in multilayer Ni–Cr coatings is found to be substantially lower. As shown by mass-spectrometric studies, hydrogen preferentially absorbs in chromium layers. The peculiarities of concurrent hydrogen evolution and chromium deposition giving supersaturated solid solutions are discussed.

A long-term cyclic voltammetry study of Pt(111) electrode in dilute solutions of mercury sulfate (5 × 10–8–5 × 10–7 M Hg2SO4 + 0.5 M H2SO4) has shown that a slow transformation of Pt(111) surface takes place. This transformation leads to a decrease in the bi-dimensional long-range order of the surface. The interpretation of the process involves the increase in mobility of Pt atoms and surface alloying in the presence of mercury. Similar processes of Pt(111) surface disordering take place in acid solution of copper sulfate with the addition of Hg2SO4. The penetration of Hg atoms beneath the Pt(111) topmost layer proceeds when only a fraction of the mercury monolayer is deposited on the electrode surface.

Initial stages of copper electrocrystallization on glassy carbon from sulfuric acid electrolytes of pH 0.3 and 3.7 are studied by the method of potentiostatic current transients on rotating and stationary ring–disk electrode. The rate of copper deposition in a 0.5 M Na2SO4 + 0.01 М CuSO4 (pH 3.7) solution is marginally higher than in a 0.5 M H2SO4 + 0.01 М CuSO4 acid electrolyte (pH 0.3) at the expense of adsorption of sulfate and hydroxide ions on the substrate surface and the copper crystals. Regularities governing the multistage discharge of copper ions, the formation of the new phase nuclei, and the deposit dissolution are analyzed. The results of the study are compared with the data on the kinetics of copper electrocrystallization on a platinum electrode. The acceleration of the copper deposition on glassy carbon in the acid solution of pH 0.3, as compared with platinum, is due to accelerated discharge of copper ions and increased number of univalent copper ions in the near-electrode layer of solution. The oxygen-containing surface groups of glassy carbon (quinone–hydroquinone, carbonyl, etc.) are probably active centers for the discharge of copper ions and three-dimensional nucleation.

Initial stages of copper electrocrystallization on glassy carbon from sulfuric acid electrolytes of pH 0.3 and 3.7 are studied by the cyclic voltammetry method on rotating and stationary ring–disk electrode. The rate of nucleation and growth of a metallic phase of copper in a 0.5 M Na2SO4 + 0.01 М CuSO4 (pH 3.7) solution is marginally higher than in a 0.5 M H2SO4 + 0.01 M CuSO4 acid electrolyte (pH 0.3). Regularities governing the multistage discharge of copper ions, the formation of the new phase nuclei, and the deposit dissolution are analyzed. No copper adlayers form on glassy carbon at potentials more positive than the equilibrium potential of a reversible copper electrode, the copper nucleation occurs via the Volmer–Weber mechanism. The oxygen-containing surface groups of glassy carbon (quinone–hydroquinone, carbonyl, etc.) are probably active centers for the discharge of copper ions and the nucleation of the new phase. The results of the study are compared with the data on the kinetics of copper electrocrystallization on a platinum electrode.

The electrochemical behavior of adsorbed NO molecules on a Pt(100) electrode has been studied in perchloric acid solutions by means of cyclic voltammetry. According to the literature data, a saturated NO adlayer with a coverage of ∼0.5 monolayers (MLs) is formed under open circuit conditions in an acidic nitrite solution as a result of a disproportionation reaction. The saturated adlayer is stable in the potential range of 0.4–0.9 V vs. a reversible hydrogen electrode in 0.1 M HClO4. NO molecules are oxidized at 0.9–1.1 V with the formation of adsorbed nitrite anions, and they can be reduced to ammonia at potentials less than 0.4 V. In this paper it has been shown that the adlayer stability depends on the surface coverage and extent of ordering. An unsaturated NO adlayer demonstrates NO ↔ NH3 redox transformations at 0.5–0.8 V. Financial support from the Russian Foundation for Basic Research (project no. 10-03-00427), MICINN (CTR2010-1624)(Feder), and Generalitat Valenciana (Prometeo/2009/045)(Feder, Spain) is gratefully acknowledged.

The catalytic and adsorption properties of platinum microparticles incorporated into polyaniline films were investigated using methanol oxidation in acidic solutions as a test reaction. The potential dependences of the specific reaction rates — the stationary oxidation currents referred to the unit of the true platinum surface were measured for different amounts of incorporated platinum (25–750 μg cm −2 ). The methanol adsorption kinetics and the dependence of the surface coverage on methanol concentration were established. The results of adsorption measurements were compared with catalytic effects. It was found that the extent of the catalytic effects and their mechanism depend on the amounts of the microdeposits and their distribution in the polymer layer. For moderate and high platinum loadings (60–750 μg cm −2 ) the specific reaction rates are higher than those on platinized platinum and increase with increasing loadings up to the reaction rate on smooth platinum. At the same time the reaction mechanism for these electrodes remains the same. It seems that the catalytic effects on such electrodes are influenced by structural peculiarities of the deposits. For low platinum loadings (25–35 μg cm −2 ) a change in the ratio of the rate of different steps can be observed as methanol adsorption becomes markedly inhibited and limits the overall reaction rate.

A long-term study of Cu UPD and OPD kinetics on the Pt(111) electrode by cyclic voltammetry and potentiostatic current transient techniques has shown that copper oxides CuxO could be considered as the active centers of the adlayer growth and further bulk copper deposition. These species are formed by a slow surface reaction between the adsorbed oxygen and copper atoms or ions at potentials E 0.55 V versus NHE. An enhanced rate of copper cations reduction on the positively charged Pt surface in the vicinity of electronegative CuxO species caused by the local electrostatic effects in the electric double layer could be the reason for the accelerating action of these active centers. © 2001 Elsevier Science Ltd. All rights reserved.

The corrosion–electrochemical behavior of chromium electrodeposits, which are formed in sulfuric acid solutions of Cr(III) containing oxalates, is studied by taking steady-state polarization measurements in a 0.5 M H2SO4 solution. No region of the metal's active dissolution is observed for such coatings, and the open-circuit potential is localized in the passivity region, i.e. it is substantially displaced in the positive direction as compared with that for metallurgic chromium or the coatings deposited from standard chromium-plating electrolytes. According to XPS data, the surface layer of the passive metal a few nanometers thick includes oxide compounds of chromium and also carbides formed during the coating electrodeposition. Specific features of the corrosion–electrochemical behavior of the deposits are attributed to the presence of carbide compounds of chromium in them, with the compounds playing the role of a cathodic alloying agent.

Initial stages of the copper electrocrystallization on platinum from a sulfuric acid electrolyte are studied by measuring potentiostatic current transients (the chronoamperometry method) on a rotating and stationary ring-disk electrode. The number of active centers and the copper nucleation rate are shown to substantially depend on the electrochemical pretreatment of the electrode. The mechanism governing the formation of intermediate species (ions Cu+) during the nucleation of a new copper phase and the deposit dissolution is analyzed.

The activation of a platinum electrode in an acid sulfate solution is studied on rotating and stationary disk electrodes by means of cyclic voltammetry. Rates of the adatom layer formation and the phase copper deposition significantly increase following use of a slow potential scan and/or agitation of electrolyte as a result of the interaction between adatoms or ions of copper with adsorbed or dissolved oxygen. Oxide compounds of copper are active centers of a two-dimensional growth of an adatom layer and a three-dimensional nucleation in the course of electrocrystallization.

Initial stages of copper electrocrystallization on platinum rotating and stationary ring-disk electrodes are studied in sulfate electrolytes of different acidities by cyclic voltammetry with a variable cathodic limit. In a weakly acid sodium sulfate solution of pH 3.7, copper deposition occurs at a higher rate than in a sulfuric acid electrolyte, which is due to an acceleration of the discharge of copper ions caused by local electrostatic effects that occur during the specific adsorption of sulfate anions and hydroxyl ions and to alterating nature of electroactive species. The mechanism of the formation of intermediate species (ions Cu+) during the deposition and dissolution of copper in solutions of different acidities is established.

The formation of copper adatom layers at polycrystalline platinum in sulfate and perchlorate solutions is studied by cyclic voltammetry on a ring-disk electrode. Specific adsorption of anions accelerates the copper underpotential deposition by decreasing the positive potential of the dense part of EDL. Of importance is the anion composition of co-adsorption lattices that form at moderate coverages of platinum by copper. Supermonolayer coatings form under the conditions of strong specific adsorption of anions. In a weakly acid sodium sulfate solution, the surface coverage by copper adatoms reaches 1.7 monolayers.

The anodic behavior of x-ray-diffractometrically amorphous chromium deposits in 1 N sulfuric acid is investigated with the use of potentiostatic and potentiodynamic techniques. The morphology of the surface of coatings was studied with digital microscopy. The substantial effect of a substrate (copper) on the anodic behavior of a porous coating is noticed. Pores and cracks may appear in the coating due to the surface somatoids formed during electroplating. The possible mechanisms of the passivation of coatings are considered.

The influences of the Cu adatoms and Cu + ions on the initial stages of copper electrodeposition on polycrystalline Pt in acidified copper sulphate solution have been studied by cyclic voltammetry, potentiostatic current transients, rotating ring-disk electrode ( rrde ), and in situ scanning tunnelling microscopy (STM). It has been established that during the long-time polarization of the platinum electrode, at potentials close to the copper equilibrium potential, the concentration of Cu + ions in the vicinity of the electrode increases and a Cu microdeposit if formed. The dissolution of the microdeposit occurs very slowly and takes several minutes of potential cycling in the range of 0.27–1.25 V. While the microdeposit is present on the platinum, the electrode surface is more active with respect to upd and bulk copper deposition. The combination of electrochemical and in situ STM results indicates that formation of surface alloy occurs during electrodeposition of copper on polycrystalline platinum.

Kinetics and mechanism of nitrate and nitrite reduction on Pt(100) electrode modified by Cu adatoms have been studied in solutions of sulfuric and perchloric acids by means of cyclic voltammetry and in situ IR-spectroscopy. It has been shown that the surface redox process with participation of ammonia or hydroxylamine at 0.5–0.9 V occurs only on the Cu-free platinum. The causes of this effect could be low adsorption energy of nitrate reduction products on copper or changes in the composition of the products (ammonia for Pt(100) and N2O for Pt(100)+Cu). Nitrate reduction on Pt(100)+Cu electrode is much faster in the perchloric acid solution (by several orders of magnitude) as compared with unmodified platinum as a result of induced adsorption of nitrate anions in the presence of partly charged Cu atoms. In the solutions of sulfuric acid the rate of nitrate reduction is considerably lower as copper adatoms facilitate adsorption of sulfate anions, which block the adsorption sites for the nitrate. The work was financially supported by the Russian Foundation for Basic Research (project no. 10-03-00427). Financial support from MICINN (CTR2010-1624) (Feder) and Generalitat Valenciana (Prometeo/2009/045) (Feder) is gratefully acknowledged.

Poly( p -phenylene) (PPP) films deposited from benzene in concentrated H 2 SO 4 emulsion reveal a highly crystalline structure under TEM, SEM and XDA in contrast to nearly completely amorphous films deposited from C 6 H 5 NO 2 medium. Possible effects of solvent and electrolyte specificity on the morphology and mechanical properties of PPP films are discussed in view of these results.