Electrodeposition of gallium onto vitreous carbon

Gallium electrodeposition onto vitreous carbon was studied in chloride solution using potentiostatic and potentiodynamic techniques. The morphology and composition of the deposits were analysed by SEM/EDX. The effects of solution pH, applied potential and the hydrodynamic conditions on the electroreduction process were investigated. Results indicate that the reduction to Ga⁺¹ species takes place at the lower overpotentials, while at high overpotentials gallium deposition occurs through progressive nucleation and growth under diffusion control. The influence of the simultaneous hydrogen evolution reaction on the electrodeposition process is discussed. This paper is dedicated to the memory of Professor J. B. Bessone who died on 23rd April 2006     

Electrodeposition of indium and zinc on aluminium

Zinc and indium were deposited from sulphate and chloride electrolytes onto aluminium electrodes under potentiostatic conditions. The role of the anion, pH, cation concentration, cathodic potential and agitation were investigated. The deposit morphology and composition were studied by SEM and EDX. Potentiodynamic and galvanostatic techniques were also applied for product characterization. Once a critical amount of Zn was deposited preferred In deposition began without agitation. But under rotation or at low cathodic potentials Zn2+ discharge became the prevalent reaction. The results support the earlier hypothesis of the preferential adsorption of Zn ions [1].     

Electrodeposition of zinc from high acid zinc chloride solutions

Electrowinning of zinc from zinc chloride solutions, acidified by HCl, was conducted in a cation exchange membrane cell. The current efficiency was correlated with the deposit morphology. The deposits having lesser surface defects, which act as active sites for hydrogen adsorption, exhibited higher current efficiency. The (1 1 0) preferred texture was observed on the deposits grown in high acid solution containing gelatin. High temperature (40 ºC) and high current density decreased the current efficiency and the preferred texture.     

锌电积用惰性阳极材料的研究现状

阐述了国内外铅及铅合金阳极、钛基二氧化铅阳极等锌电积用惰性阳极材料的研究现状,并对未来锌电积用惰性阳极材料的发展趋势进行了展望.     

电沉积法制备氮化碳晶体

氮化碳是一种比金刚石更坚硬的材料,其拥有广泛的发展和应用前景。文章采取电化学沉积方法,在尿素的甲醇溶液中制备氮化碳,通过引入NaNO3,在单晶硅表面电沉积晶体薄膜,分析了薄膜形成的过程,并用XRD、Raman等手段进行了表征,结果表明,形成的薄膜是一种氮化碳结构,并含有氧元素。     

电沉积纳米晶锌镀层的研究进展

纳米晶锌镀层具有不同于传统镀锌层的理化性质。随着晶粒尺寸的减小,其耐磨性、耐蚀性、韧性、硬度及电化学性能都将得到显著提高。介绍了碱性体系、氯化物体系、硫酸盐体系、醋酸盐体系、柠檬酸盐体系、离子液体中电沉积纳米晶锌镀层的研究进展。论述了纳米晶锌镀层的特点、典型电沉积工艺及其应用,并对脉冲电沉积纳米晶锌镀层的研究现状及其发展趋势进行了展望。     

Electrodeposition of Zn in acid sulphate solutions: pH effects

The kinetics of zinc electrodeposition from acid sulphate solution on a platinum electrode was investigated by means of stationary polarization curves, interfacial pH measurement and electrochemical impedance spectroscopy. The effect of pH, namely pH 2, 3 and 4, was analyzed. A significant dependence of Zn electrodeposition with solution pH was verified. The results obtained cannot be predicted by the available models for Zn electrodeposition. A reaction model is then proposed based on the predominant steps as a function of the potential and the electrode surface nature.     

Electrodeposition of Mesoporous Nickel onto Foamed Metals Using Surfactant and Polymer Templates

High surface area electrodes are of much interest for various applications including electrochemical detectors, batteries, and fuel cells. The development of high surface area electrodes using liquid crystal templating to enhance the surface area of three-dimensional electrodes is reported. This method uses Brij 56, a nonionic surfactant, or Pluronic P123, a triblock copolymer, to template the electrodeposition of a mesoporous nickel film onto a foamed nickel electrode. This method is found to produce a 30–35 fold increase in surface area. XRD of Pluronic P123 templated nickel on gold surfaces shows a peak consistent with a pore to pore spacing of 7.5 nanometers.     

Electrodeposition of iridium onto glassy carbon and platinum electrodes

The mechanism for the electrodeposition of iridium onto glassy carbon and platinum substrates has been investigated. Iridium coatings were characterized by X-ray photoelectron microscopy to determine their chemical compositions and the morphologies of deposits were observed by scanning electron microscopy. The deposition of iridium on glassy carbon electrodes requires, in a first stage, the formation of Ir surface sites. These sites, generated by reduction of Ir³⁺ ions for large overpotential, allow the adsorption of H atoms which act as the reducing agent for Ir³⁺ ions. In contrast, on platinum, Ir electrodeposition occurs readily due to a high H_ads surface coverage. The optimal H_ads surface coverage for the electrodeposition of Ir on Pt is close to 0.5. Electrochemical quartz crystal microbalance measurements demonstrated that the Faradaic efficiency of Ir deposition on Pt is very low (0.2–1.7%).     

电沉积制备羟基磷灰石-碳化硅复合涂层

采用电沉积技术在碳/碳复合材料表面制备出羟基磷灰石-碳化硅复合涂层,通过扫描电镜、x.射线衍射仪、能谱仪、傅里叶红外光谱仪研究了电解液浓度与电流密度对复合涂层形貌与组成的影响,采用粘接拉伸法测试羟基磷灰石-碳化硅涂层、羟基磷灰石涂层与基体的结合强度.结果表明:随着电解液浓度的降低,涂层的组成由磷酸氢钙转变为羟基磷灰石,晶体从大尺寸的片状逐渐转变为纳米级球状.随着电流密度的升高,涂层的钙、磷摩尔比逐渐升高,晶体向疏松的针状转变.选取适当的工艺参数,羟基磷灰石-碳化硅与基体结合强度高于羟基磷灰石涂层.     

电沉积碳纳米管担载金属纳米微粒复合镀层及其应用

碳纳米管因其具有独特的性能而受到越来越多的关注,其固有的特性使其成为理想的金属纳米微粒的载体。概述了电沉积法制备碳纳米管担载金属纳米微粒的工艺及其进展,同时介绍了该复合镀层在催化剂和传感器等领域的应用。     

镀锌层表面电沉积防腐蚀膜层工艺

为了提高镀锌层的耐蚀性,通过施加电压的方式,促进成膜反应的进行,在镀锌层表面制备一种耐腐蚀膜层。采用电化学工作站及中性盐雾试验测试该膜层的耐蚀性,初步确定了一种较优工艺。结果表明:经处理的镀锌层的耐蚀性较未经处理的镀锌层的耐蚀性有很大的提高。该工艺简单,并且对环境无污染。     

The preparation of PbO2 coatings on reticulated vitreous carbon for the electro-oxidation of organic pollutants

The preparation of PbO₂ coatings on reticulated vitreous carbon (RVC) has been carried out at constant current from electrolytic baths containing aqueous Pb(II) and methanesulfonic acid (MSA, CH₃SO₃H). The morphological and structural analysis of the RVC/PbO₂ deposits carried out by scanning electron microscopy (SEM) and X-ray diffraction revealed that a thick (100 μm), homogeneous, nanostructured β-PbO₂ film can be successfully formed. As a result, three-dimensional β-PbO₂ structures were obtained, being particularly interesting for their use as anodes in wastewater treatment. The high oxidation ability of these anodes has been verified by the electro-oxidation of Methyl Orange aqueous solutions. Quick decolourisation was achieved, with total colour removal in less than 60 min at 600 mA due to the production of large amounts of reactive OH radicals from the oxidation of water at high anodic potentials. The progressive mineralisation of the solutions was also ascertained from the total organic carbon (TOC) removal, which was much quicker at a higher applied current. All the coated RVC electrodes exhibited excellent long-term stability and remained unaltered after prolonged electrolyses. In addition, novel PbO₂ composite coatings were prepared in the presence of hydrothermally synthesized titanate nanotubes (TiNT). The SEM images showed the presence of TiNT agglomerates along the PbO₂ surface, which led to higher anodic current in the cyclic voltammetries carried out with Methyl Orange solutions. It is suggested that TiNT favour the adsorption of the organic molecules, facilitating the contact with the OH radicals and thus accelerating the electro-oxidation process. This was confirmed by the faster TOC removal compared to that yielded by the RVC/PbO₂, being 45% instead of 24% at 120 min.     

A Modified Hull Cell and its Application to the Electrodeposition of Zinc

An analytical electrochemical cell based on the Hull cell is described. The cell was tailored specifically for the analysis of electrowinning or electroplating. Current density distributions were generated by asymmetric insertion of an insulating baffle between parallel electrodes. The position and length of the baffle were easily altered, giving 12 possible distributions for a single total current. The cathode consisted of 10 electrically isolated 1cm², aluminium segments. By logging the potential drop across 1 resistors in each of the 10 isolated parallel branches, quantitative determination of current densities across the cathode was made possible. The small segments facilitated microscopic analysis of deposit morphologies. A technique for the determination of current efficiencies on each segment is described and demonstrated. The technique obviates the necessity to determine deposited masses directly. Development of the technique for industrial application is detailed. The system is demonstrated by evaluating known effects of variables in zinc electrowinning. The variables examined were temperature, deposition time, acid concentration and antimony contamination.     

Electrodeposition of iron oxide nanorods on carbon nanofiber scaffolds as an anode material for lithium-ion batteries

Iron oxide film with spaced radial nanorods is formed on the VGCF (vapor-grown carbon nanofiber) scaffolds by means of anodic electrodeposition. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy show that the iron oxide film deposited on the VGCF surface is α-Fe₂O₃ and consists of spaced radial nanorods having 16-21 nm in diameter after annealing at 400 °C. Galvanostatic charge/discharge results indicate that the α-Fe₂O₃/VGCF anode (970 mAh g⁻¹) has higher capacity than bare α-Fe₂O₃ anode (680 mAh g⁻¹) at 10 C current discharge. VGCF scaffolds fabricated by electrophoretic deposition favor the electron conduction, and the spaced radial nanorods on VGCFs facilitate the migration of lithium ion from the electrolyte. Electrochemical reactions between α-Fe₂O₃ and lithium ion are therefore improved significantly by this tailored architecture.     

铝–碳纳米管复合镀层的电沉积

采用有机溶剂体系在紫铜基体上电沉积制备Al–碳纳米管(CNTs)复合镀层。镀液组成为:Li Al H4 10 g/L,四氢呋喃600 m L/L,Al Cl3 100 g/L,甲苯400 m L/L,柠檬酸钠20 g/L,分散剂0.4 g/L,CNTs 1 g/L。研究了电流密度、温度、搅拌速率和电镀时间对电沉积Al–CNTs复合镀层的影响,得到较好的工艺条件为:电流密度6 A/dm2,温度25°C,搅拌速率300 r/min,时间40 min。在该工艺条件下制备的Al–CNTs复合镀层呈较光亮的灰白色,厚度约为30μm,镀层的微观表面凹凸不平,但晶粒比纯Al镀层更为细致。     

Electrochemical reduction of 2-ethyl-9,10-anthraquinoneon reticulated vitreous carbon and mediated formationof hydrogen peroxide

Hydrogen peroxide formation by the intermediate electroreduction of 2-ethylanthraquinone (EAQ) has been examined. The medium used for this preparative electrolysis was dimethoxyethane (DME) with tetraethylammonium tetrafluoroborate (TEATFB) salt as supporting electrolyte in the presence of a small percentage of water. In this process EAQ is reduced on a reticulated vitreous carbon (RVC) cathode in the presence of oxygen. It has been demonstrated that in this medium, the presence of EAQ enhances the hydrogen peroxide formation when compared to the direct reduction of oxygen in the same medium. The influence of EAQ on the oxygen reduction has also been examined by cyclic voltammetry on a vitreous carbon cathode.     

Electrodeposition of carbon films from molten alkaline fluoride media

The electrodeposition of carbon films from carbonate ions (CO₃²⁻) in molten alkaline fluorides (LiF/NaF) was investigated in the 700-800 °C temperature range using cyclic voltammetry and chronopotentiometry. The cathodic peak in the cyclic voltammogram indicates that CO₃²⁻ ions are reduced in a one-step process: CO₃²⁻+4e⁻→C+3O²⁻. Deposits of amorphous carbon were obtained by potentiostatic electrolysis and analysed by several physical techniques: X-ray diffraction, Raman spectroscopy, scanning electron microscopy coupled with energy dispersive spectroscopy.     

Cadmium and zinc adsorption onto activated carbon: Influence of temperature,pH and metal/carbon ratio

The adsorption characteristics of cadmium and zinc onto a granular activated carbon were studied. Cadmium and zinc removals increased on raising pH and temperature, and decreased on raising the molar metal/carbon ratio. The adsorption processes were modelled using the surface complex formation (SCF) Triple Layer Model (TLM) with an overall bidentate species. A dependence of the SCF constant on pH, the molar metal/carbon ratio and temperature was observed, and a correlation for log K_ads was determined. The SCF model successfully predicted cadmium and zinc removals.     

Enhanced mass transport to a reticulated vitreous carbon rotating cylinder electrode using jet flow

The mass transport characteristics of a porous, rotating cylinder electrode (RCE, 1.0 cm diameter; 0.5, 0.9 or 1.2 cm long; 1.25, 2.25, 3.00 cm³ overall volume; 250-2000 rpm speed) fabricated from reticulated vitreous carbon (RVC, 60 ppi or 100 ppi) were investigated. The deposition of copper from an acid sulfate electrolyte (typically, deoxygenated 1 mM CuSO₄ in pH 2, 0.5 M Na₂SO₄ at 298 K) was used as a test reaction. The effect of a jet flow of electrolyte towards the electrode and the introduction of polypropylene baffles in the electrochemical cell were studied at controlled rotation rates of the RCE. The product of mass transport coefficient and volumetric electrode area (k_mA_e) is related to the rotation speed of the electrode. For the 60 ppi RVC RCE, the jet electrolyte flow (3.5 cm³ s⁻¹) enhanced the mass transport rates by a factor of 1.46 at low rotation speeds; this factor was reduced to 1.08 at high rotation speeds. For a 100 ppi electrode, the enhanced mass transport decreased from 1.26 to 1.03 at low and high rotation rates, respectively. Under the experimental conditions, baffles showed little effect on the mass transport rates to the RVC RCE. Mass transport to jet flow at an RVC RCE is compared to other RCEs using dimensionless group correlation.