EQCM study of electrochemical modification of Bi2S3 films in the Zn-containing electrolyte

The electrochemical behavior of Bi₂S₃ as-deposited on Au using the successive ionic layer adsorption and reaction method has been investigated in the Zn²⁺-free background and Zn²⁺-containing electrolytes at different pH by electrochemical quartz crystal microbalance coupled with cyclic voltammetry and X-ray photoelectron spectroscopy. It has been shown that when the Bi₂S₃ film is reduced in the Zn²⁺-containing electrolyte Zn²⁺ ions are involved in electrochemical bismuth sulfide reduction and are partially reduced together with the bismuth sulfide film. The bismuth sulfide film initiates the adsorbed Zn²⁺ ions reduction prior to the traditional overpotential deposition of it. Reduction of Zn²⁺ ions prior to the overpotential deposition of Zn depends on solution pH: at pH 5 it occurs at more negative potential values and the observed mass changes due to Zn electrodeposition are greater than at solution pH 3. After bismuth sulfide film reduction in the Zn²⁺-containing electrolyte, Zn was detected as ZnO and metallic Zn at pH 5, while at pH 3 only ZnO was detected.     

EQCM study on the oxidation/reduction of bismuth sulfide thin films

The oxidation/reduction of bismuth sulfide thin films deposited on an Au electrode using the successive ionic layer adsorption and reaction method has been investigated by electrochemical quartz crystal microbalance combined with cyclic voltammetry and X-ray photoelectron spectroscopy. It has been shown that the oxidation/reduction of bismuth sulfide film depends on the nature of anion. In the acetate solution the bismuth sulfide film is oxidized at more negative potential values than that in sulfuric acid solution. During the oxidation of bismuth sulfide film the Bi present on the surface of the bismuth sulfide film is oxidized first. This process is followed by subsequent oxidation of bismuth sulfide film alongside the oxidation of Au. In the acetate background solution the oxidation of bismuth sulfide occurs with the whole film stripping and the calculated amount is related to the amount of deposit and corresponds to the thickness of ∼9–10 nm. In sulfuric acid the bismuth sulfide film is not completely stripped out in one anodic cycle. The evaluated amount during the first anodic scan corresponded to the thickness of deposit of ∼3–4 nm. The reduction of bismuth sulfide film took places at more positive potential values in the acetate background solution than that in sulfate background solution at pH 4. After the reduction of bismuth sulfide film to Bi⁰ and S²⁻ in the background solution, depending on the nature of anion, the oxidation of metallic Bi proceeds by two different mechanisms: in the sulfate solution Bi is oxidized to Bi(III) oxygen compounds while in the acetate solution Bi is oxidized by dissolution.     

Electrocatalytic behavior of Pt-modified polyaniline electrode for methanol oxidation: Effect of Pt deposition modes

Platinum dispersed in polyaniline film is a better catalyst than bulk platinum for methanol electrooxidation in sulfuric acid solution. The effect of deposition modes of platinum particles on their electrocatalytic activity has been studied. Several electrodeposition methods, including constant potential, cyclic potential and double potential step, have been applied to characterize the performance of different electrodeposition modes. Besides the variation of the electrodeposition methods, rotating disk electrode technique is applied to disperse Pt particles under the control of convection–diffusion condition. The results show that the enhanced electrocatalytic activity may be due to the dispersion of Pt particles in the polyaniline film matrix and the synergistic effects between the dispersed Pt particles and the polyaniline film. Variables related to reaction kinetics, such as mass transport of species, concentration of methanol and acidity of solution, are investigated and reaction mechanism for methanol oxidation is discussed.     

Cathodic behavior of bismuth. I. Ellipsometric study of the electroreduction of thin Bi2O3 films

The electroreduction of thin Bi₂O₃ films was characterized by employing electrochemical techniques and in situ ellipsometry. The electroreduction optical response is described in terms of a bilayer model. The optical analysis indicates that electroreduction proceeds yielding a rough/porous layer of metallic bismuth at the oxide/electrolyte interface, that grows inwards at the expense of the underneath oxide layer to completely exhaust it. At the end of oxide electroreduction, the aging process of the porous metallic bismuth layer could be detected. On this framework, changes in the oxide growth kinetics observed on electroreduced surfaces can be consistently explained.     

Composite WO3–TiO2 films prepared by pulsed electrodeposition: morphological aspects and electrochromic behavior

This study builds upon on an earlier communication from our group [Electrochem. Commun. 5 (2003) 220] that described the preparation, by pulsed cathodic electrodeposition, of WO₃–TiO₂ composite films over a wide compositional range. We focus here on the morphology of these composite oxide films as probed by scanning tunneling microscopy and their electrochromic behavior. It is shown that the progressive coloration of an initially transparent conducting oxide glass substrate, as a result of oxide film growth, offers a versatile spectroelectrochemical probe of the film electrosynthesis process itself. Finally, both the blue shift undergone by the absorption threshold of the oxide film (as a result of electron accumulation during the electrochromic process), and the coloration dynamics are favorably influenced by the presence of small amounts of TiO₂ in the WO₃ film.     

Electrochemical preparation of polypyrrole-molybdenum trisulfide-tetrathiomolybdate electrode with various amounts of molybdenum species

Polypyrrole films doped with molybdenum trisulfide and tetrathiomolybdate anions have been prepared from an aqueous solution containing pyrrole and ammonium tetrathiomolybdate in the presence of tiron, (4, 5-dihydroxy-1, 3-benzenedisulfonic acid), in the deposition solution. In such a solution the electrodeposition of polypyrrole doped with tetrathiomolybdate anions is in competition with the electrodeposition of molybdenum trisulfide by oxidation of tetrathiomolybdate anions. Our results indicate that the relative amounts of polypyrrole and molybdenum species can be varied over larger ratios when tiron is present in the deposition solution. The variation of the amount of molybdenum species can be explained by considering the number of electrons required to generate one mole of tetrathiomolybdate as dopant for polypyrrole and one mole of molybdenum trisulfide; 14 electrons are required per mole of tetrathiomolybdate incorporated in the polymer in comparison to 2 electrons per mole of molybdenum trisulfide generated directly by electrochemical oxidation of tetrathiomolybdate. Tiron acts as a catalyst for the deposition of polypyrrole and in this case the relative amount of polypyrrole in the composite film electrode is larger. For higher tetrathiomolybdate concentration, the direct formation of molybdenum trisulfide occurs preferentially and the catalytic effect of tiron is less important.     

Voltammetric study of the influence of EDTA on the silver electrodeposition and morphological and structural characterization of silver films

The electrodeposition of silver onto platinum from an alkaline electrolyte containing EDTA (ethylenediaminetetraacetic acid) was investigated. Voltammetric studies indicated that the reduction process is influenced thermodynamically and kinetically by the EDTA concentration. Moreover, hydrodynamic studies showed that silver deposition involved different silver complexes, depending on the EDTA concentration. Scanning electron microscopy analysis showed that the presence of EDTA in the plating bath was beneficial, since the silver films coated the substrate completely, regardless of the EDTA concentration. Furthermore, the silver films were uniform, without cracks and with fine granularity, while in the absence of EDTA the granularity was rough. Energy dispersive X-ray spectroscopy showed that carbon was not incorporated into the silver films. X-ray diffraction analysis of the Ag deposits obtained at various EDTA concentrations indicated the occurrence of polycrystalline silver and that the main orientation was (1 1 1), as found in the silver film obtained from a cyanide bath.     

Electrochemical growth and characterization of size-quantized CdTe thin films grown by underpotential deposition

Size-quantized thin films of CdTe were electrosynthesized onto Au(1 1 1) substrates by underpotential deposition (UPD) from an acidic aqueous solution of CdSO₄, and TeO₂. The electrodeposited thin films were characterized by scanning tunneling microscopy (STM), atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and UV–vis absorption spectroscopy. The electrodeposition mechanism and the codeposition potential of CdTe were explored by cyclic voltammetry. The voltammetric analysis indicates that the electrodeposition of CdTe is a two-step codeposition process under the conditions of UPD. Morphological investigations demonstrate that the film growth proceeds via the formation of a few layers, growth of spherical nanoparticles on the overlayer and then continues by growth to form smooth spherical crystallites of CdTe. XRD results show that the growth of films are highly preferential with (1 1 1) orientation. Optical studies revealed blue shift in band gap energy due to quantum confinement.     

Electrochemical oxidation of o-aminophenol in aqueous acidic medium: formation of film and soluble products

The electrochemical oxidation of o-aminophenol (OAP) has been studied by cyclic voltammetry on platinum (Pt) and glassy carbon (GC) electrodes. Films formed on Pt exhibited a voltammetric response that is dependent on the final potential applied during the electropolymerization. Although a less electroactive film has been obtained on Pt electrodes cycled at higher potentials, modified GC electrodes showed a well-defined redox response independently of the potential range used. This result is attributed to an activation process of the GC electrode rather than to an electroactive film deposited on the electrode. The deposition process of thin films was also investigated with quartz crystal microbalance experiments. Poly-o-aminophenol (POAP) films were insoluble with an electrochromic response from colorless to brown, and a ladder structure confirmed by infrared spectra. Exhaustive electrolysis of OAP produced a reasonable amount of soluble product, which after solvent extraction, was characterized as 2-aminophenoxazin-3-one (APZ), a product also prepared by chemical oxidation of OAP. A route of electrooxidation of OAP has been proposed based on electrochemical and spectroscopic results.     

Electrochemical and X-ray absorption spectroscopy studies of copper coatings on a hydrogen storage alloy

Electroless copper deposits were made on the surface of LaNi_4.7Sn_0.3 particles with the aim of studying the influence on the charge/discharge performance of this metal hydride alloy. Cu layers were produced using formaldehyde and hydrogen as reducing agents and the near-range order and composition investigated as a function of deposition method by X-ray absorption spectroscopy. The electroless layer deposited using formaldehyde was shown to be mainly in the metallic state (Cu⁰). The copper layer prepared using hydrogen resulted in a mixed phase formed by metallic and oxidized copper species. Results also indicated that the copper layer protects the Ni atoms against corrosion, but this does not help in capacity retention during the charge/discharge cycling of the alloy. The electrode coated with the hydrogen reduced copper layer had lower discharge overpotentials relative to the uncoated electrode, implying an increase in the exchange current density for the process.     

Study of the influence of the polyalcohol sorbitol on the electrodeposition of copper–zinc films from a non-cyanide bath

The electrodeposition of copper–zinc on to AISI 1010 steel from an alkaline non-cyanide solution containing sorbitol was investigated, with various proportions of the metal ions in the bath. Voltammetric curves indicated that the complexation of copper ion by sorbitol is beneficial, since the copper complex reduction potential is close to that of the zincate ion, implying that codeposition of copper and zinc should occur. EDS analysis showed that varying the ratio of copper to zinc ions in the plating bath affects the proportion of metals in the deposits, leading to golden or greyish bright films, even in the high-hydrogen-evolution potential region, indicating that sorbitate anions prevent the deposits becoming darker in this region. The narrow variation in film colour at various deposition potentials and charge densities showed that rigorous control of the alkaline-sorbitol plating bath and deposition conditions is not necessary. SEM analysis showed that the films were without stress and the substrate was fully covered. X-ray spectra suggested that a mixture of Cu₈0 and CuZn₂ alloy was deposited at ?1.14 V in all the baths studied while Cu_0.61Zn_0.39 (Cu-70 bath), Cu₅Zn₈ (Cu-50 bath) and CuZn₅(Cu-30 bath) films were deposited at both ?1.45 and ?1.60 V.     

Voltammetric and EQCM investigation of conductive films formed by electroreduction of Ru(L)(CO)2Cl2 compounds

Electroreduction of trans(Cl) and cis(Cl)Ru(L)(CO)₂Cl₂ (L=bpy=2,2′-bipyridine, dmbpy=4,4′-dimethyl-2,2′-bipyridine) in CH₃CN and DMSO resulted in electrode-adhering films and the reactions were studied by voltammetry and the electrochemical quartz crystal microbalance. These methods were complemented by hydrodynamic rotating ring-disc and quartz crystal impedance methods. The deposition was strongly influenced by the type of solvent, polarisation mode and electrolyte stirring, but for all compounds, rapid charge transfer was found. For monomers with trans(Cl)Ru(bpy)(CO)₂Cl₂, the two-electron reduction and Ru⁰Ru⁰ polymerisation process suggested in the literature was confirmed. Some adsorption of CH₃CN was also indicated and for potentiostatic deposition in static solution the impedance measurements indicated increased film viscoelasticity. Depositions with cis(Cl)Ru(bpy)(CO)₂Cl₂ were more complex and the rate declined gradually in static solution. In stirred solution a straightforward polymer formation took place. For trans(Cl)Ru(dmbpy)(CO)₂Cl₂ the literature mechanism could not be confirmed and large deviations were observed during the early stages of deposition. The trans(Cl) dimer, [Ru(bpy)(CO)₂Cl]₂ displayed a lower current efficiency during film formation than the monomer and no simple deposition mechanism could be suggested. For the trans(Cl)[Ru(dmbpy)(CO)₂Cl]₂ dimer a straightforward deposition was found. The films could be removed by electrooxidation and mass/charge data show that the films break up in large fragments. The reduction and deposition process for trans(Cl) monomers (L=bpy, dmbpy) was light sensitive and the mass of films deposited during cyclic voltammetry (CV) was doubled when the electrode was irradiated.     

EIS study of solid-state transformations in the passivation process of bismuth in sulfide solution

Anodic oxidation of polycrystalline bismuth in alkaline medium, containing sulfide ions was investigated in situ. Cyclic voltammetry was used to define the potential regions of formation and stability of anodic Bi₂S₃ and Bi₂O₃ semiconductor films that translate bismuth to the passive state. The mechanism of elementary steps of the passivation process has been investigated using electrochemical impedance spectroscopy (EIS). The electric and dielectric properties of anodic films and structural parameters of the interfaces Bi–growing film–electrolyte in a wide region of potentials and frequencies of six decades, were determined. The EIS data have been analyzed and discussed in the frame of the point defect model (PDM) of anodic film formation and growth. The growth of passive surface films on bismuth takes place via transport of anionic vacancies generated at the metal–film interface. The slow step of the process is the layer-limited diffusion of anionic vacancies (D≈ 10^?16 cm² s^?1).Solid-state transformation of sulfide to the oxide film is a consequence of OH^? ion capture into the anionic vacancies of the sulfide film, the generation and transport of cation vacancies from the film–solution interface, their annihilation and formation of a vacancy condensate of a critical size at the metal–film interface.     

Rhodium electrodeposition on pyrolytic graphite electrode: Analysis of chronoamperometric curves

The electrodeposition of metallic rhodium on pyrolytic graphite from 10 mM Na₃RhCl₆ +0.5 M NaCl aqueous solution was investigated for the first time. From the analysis of chronoamperometric curves, the nucleation kinetics was compared for two-dimensional (2D) and three-dimensional (3D) electrodeposition processes, applying various models. Rh electrodeposition at ?172 and ?232 mV vs. Ag/AgCl was interpreted in terms of 3D process of progressive type which turns into instantaneous one at more negative potentials. The principal nucleation parameters (nucleation rate constant, nucleation density) are calculated by using two frequently used models for 3D nucleation and growth (Scharifker–Mostany and Mirkin–Nilov–Heerman–Tarallo), using different fitting procedures. It is shown that both models give similar results.     

Electrochemically deposited thin films of amorphous Fe–P alloy: Part I. Chemical composition and phase structure characterization

Thin Fe–P alloy films (0.5 to 25.0 μm thick) were electrodeposited from sulfate solutions. The influences of various deposition conditions (current density, time, pH and temperature) on the composition and structure of the deposited films were examined. These Fe–P films were first characterized by the ALSV. The voltammograms obtained show several current peaks, indicating the presence of several different phase structures in the deposit. Chemical composition of the phase structures in the film was determined by EDX analysis and the amorphous nature of the alloy was verified by XRD and DTA techniques. Chemical and phase structure compositions of the alloys (containing 15–50 at.% P in the form of phosphides FeP, Fe₂P and/or Fe₃P) were found to depend on deposition conditions. Appearance and morphology of the film alloys were also found to depend on deposition conditions, particularly current density, as illustrated by the SEM technique.     

Metalloporphyrin electropolymerization: electrochemical quartz crystal microgravimetric studies

The electrochemical quartz crystal microbalance (EQCM) study of several metalloprotoporphyrin (MPP) deposition (Ni(II)PP, Cu(II)PP, Co(II)PP, Zn(II)PP, Fe(III)PP) on gold surfaces from dichloromethane solution is reported. The QCM mass–time evolution during film deposition has shown for all porphyrins studied a monotonic film growth during the positive voltammetric scan which is consistent with the accepted vinyl cation electropolymerization (EP) mechanism [J. Am. Chem. Soc. 105 (1983) 5601]. Quartz crystal impedance at 10 MHz has shown that NiPP, CuPP, ZnPP and FePP films dissipate the acoustic wave much less, rendering acoustically thinner films than a CoPP film that behaves as a loose viscoelastic film. For the former acoustically thin films, gravimetry was possible; unlike CoPP films where the viscoelastic properties are dominant at 10 MHz. Comparison of the redox charge and QCM mass demonstrates that homogeneous chemical reactions coupled to the electroinitiation of vinyl cations should take place, and therefore the application of the Faraday Law to estimate the polymer mass from the oxidation charge is precluded. The optimal EP conditions to deposit single and mixed films are also described.     

钛表面ALD构建氧化锌纳米薄膜及其性能研究

目的 比较研究原子层沉积法(atomic layer deposition, ALD)不同沉积周期制备氧化锌(ZnO)纳米薄膜的理化特点及其抗菌效应。方法 根据不同的沉积周期，将实验分为4组(光滑钛组、300循环组、600循环组、1 200循环组)。以二乙基锌、水为前驱体，在纯钛试件表面利用ALD技术制备氧化锌纳米薄膜。采用扫描电子显微镜(SEM)观察薄膜表面形貌，能谱仪(EDS)和X射线衍射仪(XRD)检测薄膜的元素组成和晶型，水接触角检测仪检测薄膜的亲水性，椭偏仪检测镀膜厚度。通过CCK-8实验、光密度法评估薄膜的细胞毒性及其对金黄色葡萄球菌的体外抗菌效果。结果 SEM结果显示ALD在纯钛表面制备的薄膜均匀致密，晶粒尺寸随着沉积周期增加而增大，EDS、XRD结果显示镀膜主要由Zn、O元素构成，成分为氧化锌晶体。水接触角结果显示薄膜为疏水。椭偏仪结果显示各实验组薄膜厚度为纳米级，与沉积周期之间呈线性关系。各实验组均未表现出细胞毒性，具有体外抗金黄色葡萄球菌效果，1 200循环组在24、48 h表现出最高抗菌率，分别为65.9%和52.3%,效果最佳。结论 ALD法在纯钛表面制备的不同...     

Effect of multi-walled carbon nanotubes as second phase on the copper electrochemical reduction behavior for fabricating their nanostructured composite films

Nanostructured copper/multi-walled carbon nanotube (Cu/MWCNT) films have been fabricated by means of pulse electrodeposition in an acidic plating bath containing copper sulfate and purified MWCNTs. The influence of MWCNTs on copper electrochemical reduction behavior is studied by cathodic polarization and electrochemical impedance spectrums (EIS) analysis. Results show that the existence of the hydrochloric acid purified MWCNTs in the electrolytes shows the accelerating action toward Cu electrochemical reduction during the electrodeposition process, making the Cu films finely grow with the crystal growth toward the (1 1 1) orientation compared to the pure Cu electrodeposited film. The resulting Cu/MWCNT composite film is comprised of Cu matrix and the spatial network of MWCNTs with a considerable high MWCNT content.     

One-step electrodeposition of ZnO/eosin Y hybrid films from a hydrogen peroxide oxygen precursor

The deposition of eosin Y/zinc oxide hybrid films is performed by cathodic electrodeposition from a hydrogen peroxide oxygen precursor in chloride medium. Typically the deposition bath contains 5 mM ZnCl₂, 10 mM H₂O₂ and less than 10 μM eosin Y. A rotating disk substrate is used with a rotation speed of 500 rpm. The deposition potentials range between ?1.25 and ?1.50 V versus the mercurous sulfate electrode (MSE). The resulting films are well crystallised and highly textured with the c axis perpendicular to the substrate. They exhibit an electrocatalytic activity for hydrogen peroxide reduction during the deposition. The role of reduced eosin bound to ZnO in the electrocatalysis is discussed. We have measured a maximum of dye loading at 0.21 M and we show that the dye is concentrated in the film compared to the dye/zinc ion molecular ratio in solution. The dye loading decreases slightly with deposition overvoltage. We discuss the loading mechanism in the light of the dye diffusion behaviour in solution and of the relationship between dye loading and film growth rate. The chemical diffusion coefficient of eosin Y under the present conditions is measured an equal to 1.9×10^?5 cm² s^?1. We show that the complexation between reduced eosin Y and free zinc ion in solution and the coprecipitation reaction of this complex are likely to be the key steps of the loading process.     

Study of the electrochemical deposition and properties of cobalt oxide species in citrate alkaline solutions

Glassy carbon electrode substrates coated with thin films of cobalt oxyhydroxide were investigated in moderately alkaline medium by cyclic voltammetry. The cobalt oxide formation process was accomplished in alkaline solution (30 mM NaOH) containing millimolar concentrations of CoCl₂ and ligand species such as sodium citrate. The cobalt oxide/hydroxide films were obtained either by voltage cycling between 0.4 and 1.1 V versus SCE or under potentiostatic conditions at moderate positive potentials (i.e. 0.5 V). The resulting electrodeposited film was characterized electrochemically in alkaline solutions by cyclic voltammetry and, independently of the electrodeposition procedure adopted, reveals three well-defined sets of redox waves related to the Co(OH)₂/Co₂O₃, Co₂O₃/CoOOH and CoOOH/CoO₂ electrochemical transitions. The charge/discharge processes and the oxygen evolution reaction during continuous potential cycling were severely inhibited in the presence of increasing concentrations of electroinactive electrolytes (i.e. NaNO₃, K₂SO₄, Na₃PO₄, etc.). The electrochemical behaviour of the electrodeposited cobalt oxide/hydroxide film in alkaline solution and in the presence of various organic molecules was also investigated.