Electrochemical behavior of a novel palladium pentacyanonitrosylferrate modified aluminum electrode

Novel inorganic film modified electrodes have been prepared by chemical deposition of a thin palladium pentacyanonitrosylferrate (PdPCNF) film on the surface of aluminum substrate. The modification process including the electroless deposition of metallic palladium on the aluminum electrode surface from PdCl₂+25% ammonia solution and chemical derivatization of deposited palladium to the PdPCNF film in 0.1 M Na₂[Fe(CN)₅NO]+0.5 M KNO₃+HNO₃ solution (pH 1.5-2.5), are described. The aluminum-based modified electrodes exhibit, one pair of well-defined voltammetric peaks which correspond to the Fe(III)/Fe(II) transition in complex structure. The effect of pH, ammonium, alkali metal and alkaline earth metal cations of supporting electrolyte on the electrochemical characteristics of the modified electrode was studied in detail. Diffusion coefficients of hydrated ammonium and alkali metal cations in the film (D), transfer coefficient (α) and transfer rate constant for electron (k_s), were determined. The high stability of this modified electrode makes it attractive in practical application.     

Nanoporous Ag and Pd foam: Redox induced fabrication using electrochemically deposited nanoporous Cu foam with no need to any additive

A simple, rapid and green method for fabrication of nanoporous metal (Ag and Pd) foams using electrochemically deposited nanoporous copper foam is presented. Ideally direct electrochemical formation of Ag and Pd foam structures without any additive reagent does not lead to a desired result; however, indirect fabrication starting from electrochemically fabricated Cu foam seems promising. Highly porous copper foam is fabricated electrochemically at a copper sheet and in turn serves as a hard template and a redox inducer for the deposition of Ag or Pd. The redox induced replacement of copper foam with Ag or Pd is done via simple immersion of as-fabricated nanoporous copper foam in cation aqueous solutions of Ag or Pd. The surface morphology of the as-fabricated foam is characterized by scanning electron microscopy (SEM), EDX and X-ray diffraction. The hydrogen evolution reaction is investigated as an example to demonstrate the electrocatalytic ability of as-fabricated foams.     

Copper deposition and its replacement by platinum on a gold electrode

The decoration of single crystal gold electrodes with platinum using underpotential deposited copper as an intermediate has been studied in detail. It was found that a significant fraction of the copper is lost in the transfer process from the upd cell to the exchange cell. In addition the surface of the gold is not covered uniformly by the platinum. Nevertheless, acceleration of the electroreduction of oxygen was observed with a loading of 0.14 μg cm⁻². The structure of the decorating layer was studied by scanning electron microscopy and atomic force microscopy.     

铜阳极泥脱铜渣中金、银、钯含量测定

建立了连续测定铜阳极泥脱铜渣中金、银、钯含量的分析方法,并与火试金法进行比较。首先,利用硝酸+乙二胺四乙酸（EDTA）+酒石酸消解铜阳极泥脱铜渣,得到含有银、钯和少量金的消解液,考察了硝酸、EDTA和酒石酸用量对消解效果的影响。结果表明,硝酸、EDTA和酒石酸用量分别为30mL、3mL、1.5g时,消解效果最好。然后,利用王水对残渣进行二次消解,得到含有金和少量银、钯的消解液,考察了王水用量对消解效果的影响。结果表明,王水用量为15mL时即可完成消解。最后采用火焰原子吸收光谱仪测定消解液中的金、银、钯含量。采用本方法测定铜阳极泥脱铜渣,Au、Ag、Pd各元素相对标准偏差均小于1%（n=10）,加标回收率在95.57%～98.70%之间,实验结果准确可靠、重现性好,与火试金法测定结果相一致。     

镍、钴、钯镀层的防铜渗性能比较

以镍、钴、钯镀层作为铜基体镀金的防渗铜中间层可以有效地防止铜原子扩散到金属表面。采用ＳＥＭ、ＥＤＡＸ、ＸＲＤ等方法研究铜在中金属内的扩散机理和扩散系数,探讨了扩散过程与这３种金属晶体结构、晶粒大小以及Ｘ－射线衍射特性的关系。     

Ultrathin platinum-group metal coated hierarchical flowerlike gold microstructure: Electrochemical design and characterization

The deliberate tailoring of hierarchical flowerlike gold microstructure (HFGMs) at the ultrathin level is an ongoing challenge and could introduce opportunities for new fabrication and application in many fields. In this paper, a templateless, surfactantless, electrochemical strategy for fabrication of ultrathin platinum-group metal coated HFGMs is proposed. HFGMs were prepared by simple electrodeposition on an indium tin oxide (ITO) substrate. The resulting HFGMs enables the deposition of an ultrathin overlayer through copper underpotential deposition (UPD), followed by spontaneous replacement of the copper with the platinum-group metal to yielded a uniform and ultrathin Pt-group metal layer on the HFGMs surface. Thus prepared bimetallic “core-shell” sample has been characterized by cyclic voltammetry, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray maps and X-ray diffraction (XRD). This is a very general and powerful technique for the fabrication of hierarchical, ultrathin coating, bimetallic “core-shell” microstructure, which, in turn, opens up the possibility of building more complex multicomponent hierarchical microstructure with potential application, such as electrocatalysis, biosensors and nanodevices, etc.     

Electrochemical characteristics of dopamine oxidation at palladium hexacyanoferrate film, electroless plated on aluminum electrode

A novel electrode material was obtained at an aluminum electrode (Al) by a simple electroless method including two consecutive procedures: (i) the electroless deposition of metallic palladium on the Al electrode surface from PdCl₂ + 25% ammonia solution and (ii) the chemical transformation of deposited palladium to the palladium hexacyanoferrate (PdHCF) films in a solution containing 0.5 M K₃[Fe(CN)₆]. The modified Al electrode demonstrated a well-behaved redox couple due to the redox reaction of the PdHCF film. The PdHCF film showed an excellent electrocatalytic activity toward the oxidation of dopamine (DA). The effect of solution pH on the voltammetric response of DA has been investigated. A linear calibration graph was obtained over the DA concentration range 2-51 mM. The rate constant k and transfer coefficient α for the catalytic reaction and the diffusion coefficient of DA in the solution D, were found to be 4.67 × 10² M⁻¹ s⁻¹, 0.63 and 2.5 × 10⁻⁶ cm² s⁻¹, respectively. The interference of ascorbic acid was investigated and greatly reduced using a thin film of Nafion on the modified electrode. The modified electrode indicated reproducible behavior and a high level stability during electrochemical experiments, making it particularly suitable for the analytical purposes.     

Electrochemical phase formation—I. The electrodeposition of copper on glassy carbon

The electrochemical phase formation of copper on glassy carbon was studied by using linear sweep stripping voltammetry and cyclic voltammetry. The underpotential deposition (UPD) of copper is shown to occur either by nucleation growth processes or adsorption-desorption processes depending on the nature of glassy carbon surface. The bulk deposition processes were found to be independent of the presence or absence of UPD copper on the glassy carbon surface. Similar results were obtained for bulk deposition studies of copper on graphite substrate.     

Effect of a vacuum-deposited metal film on the CV of the Li insertion/extraction reaction at a graphitized carbon fiber electrode

A metal film of silver, copper, or gold was vacuum-deposited on the surface of mesophase pitch-based carbon fiber prepared at 3100 °C, and the Li insertion/extraction behaviour was examined by measuring the cyclic voltammogram (CV) for various film thicknesses in a non-aqueous electrolyte containing 1 M LiClO₄. The peak height of the CV was examined in detail for the deposited silver film. The peak height increased at first with increasing film thickness up to 150 Å, but then began to decrease. At around 200 Å, a minimum peak height which was nearly the same as that of the pristine sample was observed. The peak height then increased again up to a film thickness of 400 Å, where it was two times higher than that of pristine sample, then decreased gradually. Such a complicated CV could not be observed with a gold or copper film where the enhancing effect was monotonous and more remarkable with a thinner film. X-ray diffraction patterns of the silver film deposited on the carbon fiber showed a strong crystal orientation to the carbon substrate like epitaxial growth, which was found to be dependent on both the thickness and the deposition rate. The CV peak height correlated well with the silver crystal orientation, implying that the electrochemical reaction rate differs on different crystal faces. Such could not be found in the case of gold or copper. The peak enhancing effect and the cycle behaviour were elucidated in view of the nature of solid electrolyte interphase (SEI), conductivity, and the effect of alloy formation.     

The influence of gold nanoparticle modified electrode on the structure of mercaptopropionic acid self-assembly monolayer

The comparison of assembly structure and property of mercaptopropionic acid (MPA) self-assembled monolayers (SAMs) on gold nanoparticle modified electrode (nanogold electrode) with that on planar gold electrode was studied by cyclic voltammetry (CV). The electron transfer of through the MPA SAMs and Cu underpotential deposition (UPD) on MPA-covered electrode indicated that MPA molecules assemblied on the planar gold electrode could form a very compact layer, which could surpass the electron transfer K₃Fe(CN)₆ greatly, whereas on the surface on the nanogold, which curvature make the compact packing loose. The reductive desorption in 0.5 M KOH and oxidative desorption in phosphate buffer solution (PBS) (pH 6.8) showed that gold nanoparticles could enhance the Au-S bond and stabilize the MPA molecules.     

Adsorption of mercaptopropionic acid onto Au(1 1 1): Part II. Effect on copper electrodeposition

Copper deposition in the presence of an organic additive (3-mercaptopropionic acid, MPA) was studied by cyclic voltammetry and in situ scanning tunneling microscopy (STM) and the results are compared to those for additive-free solutions. It is shown that underpotential deposition (upd) of copper onto a fully MPA-covered electrode produces a defect-rich substrate, but the defects are blocked by the dense organic film for bulk deposition, resulting in a low number of nuclei. A grain-refining effect of MPA, however, was found, when Cu deposition was initiated shortly after addition of MPA to the solution, i.e., for a low-coverage MPA adlayer.     

Electrodeposition of copper in the presence of cadmium

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

Electrochemical behavior of ruthenium (III), rhodium (III) and palladium (II) in 1-butyl-3-methylimidazolium chloride ionic liquid

Electrochemical behavior of ruthenium (III), rhodium (III) and palladium (II) in 1-butyl-3-methylimidazolium chloride (bmimCl) and their ternary and binary solutions in bmimCl was studied at various working electrodes at 373 K by cyclic voltammetry and chronoamperometry. Ruthenium (III) chloride forms a stable solution with bmimCl and the cyclic voltammogram of ruthenium (III) in bmimCl recorded at glassy carbon electrode consisted of several redox waves due to the complex nature of ruthenium to exist in several oxidation states. Electrolysis of ruthenium (III) chloride in bmimCl at the cathodic limit of bmimCl (−1.8 V (vs. Pd)) did not result in ruthenium metal deposition. However, it was deposited from bmimPF₆ and bmimNTf₂ room temperature ionic liquids at −0.8 V (vs. Pd). The electrochemical behavior of ruthenium (III) in bmimCl in the presence of palladium (II) and rhodium (III) was studied by cyclic voltammetry. The presence of palladium (II) in bmimCl favors underpotential deposition of ruthenium metal. The nuclear loop at −0.5 V (vs. Pd) was observed in all solutions when palladium (II) co-existed with other two metal ions. Nucleation and growth of the metal on glassy carbon working electrode was investigated by chronoamperometry. The growth and decay of chronocurrents has been found to follow the instantaneous nucleation model with three-dimensional growth of nuclei.     

Electrical properties of thin-films of the mixed ionic-electronic conductor CuBr: influence of electrode metals and gaseous ammonia

The electrical properties of sputtered thin-films of CuBr are measured using gold or copper electrodes and in presence of ammonia. The I–V characteristics are strongly dependent on the choice of the electrode metal: an ohmic response is observed with copper electrodes, which act reversibly for ion exchange, but exponential dependencies are measured with blocking gold contacts. An increase of the film resistance is observed in presence of ammonia: the response time is very short and the signal is reversible.     

Fabrication of a nanostructure thin film on the gold electrode using continuous pulsed-potential technique and its application for the electrocatalytic determination of metronidazole

This paper demonstrates a new and simple approach based on a continuous pulsed-potential (CPP) method for the preparation of reproducible nanostructure and nanoporous thin film on the polycrystalline gold electrodes. The fabrication process involves pulsed electrochemical oxidation and reduction of gold electrode in the sulfuric acid solution without using additional reagents. Effect of various parameters including pulse height, pulse time, pulse number and relaxation time on the enhancing of hexacyanoferrate (HCF) redox behaviour, as a probe, were investigated and optimized. Electrochemical, scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies show the formation of a nanoporous thin film and sharp nanostructure edges on the gold electrode that considerably enhances electrocatalysis of HCF and provides useful conditions for the electroanalysis by the modified electrode. In addition, the electrocatalytic behaviour of this modified electrode was exploited as a sensitive detection system for the determination of metronidazole in pharmaceutical and human urine samples, by using cyclic voltammetry (CV) and hydrodynamic methods. Under optimized conditions, this method shows linear dynamic ranges of 0.5-10.0 and 20.0-800.0 μM with the calculated detection limit (S/N = 3) of 0.15 μM and a precision of <5%.     

Hydrogen sensor based on a graphene – palladium nanocomposite

A composite material was prepared from graphene and palladium nanoparticles (PdNP) by layer-by-layer deposition on gold electrodes. The material was characterized by absorption spectroscopy, scanning electron microscopy, Raman spectroscopy and surface plasmon resonance. Cyclic voltammetry demonstrated the presence of electrocatalytic centers in the palladium decorated graphene. This material can serve as a sensor material for hydrogen at levels from 0.5 to 1% in synthetic air. Pure graphene is poorly sensitive to hydrogen, but incorporation of PdNPs increases its sensitivity by more than an order of magnitude. The effects of hydrogen, nitrogen dioxide and humidity were studied. Sensor regeneration is accelerated in humid air. The sensitivity of the nanocomposite depends on the number of bilayers of graphene–PdNPs.     

铜铝双金属复合离子液体的电化学行为及电沉积铜机理

铜铝双金属复合离子液体是新型碳四烷基化技术所用的绿色催化剂,电化学处理是回收工业应用过程外排复合离子液体中金属铜的有效途径之一,为此需要深入研究其电化学行为和电沉积铜机理。循环伏安研究发现,铜铝双金属复合离子液体在Pt盘电极、W盘电极和玻碳电极上的还原过程均包括铜的欠电势沉积、Cu(Ⅰ)的还原和铜的超电势沉积,氧化过程均包括Cu→Cu(Ⅰ)、Cu(Ⅰ)→Cu(Ⅱ)。计时安培研究表明,铜的成核方式为三维瞬时成核。长周期实验结果显示Cu(Ⅰ)的浓度随着时间下降的趋势变缓,表明电沉积铜速率逐步下降。电沉积电势对沉积产物的形貌影响较大,-2.60 V下的产物形貌更平整致密。XRD结果表明在-1.20~-2.60 V电势下阴极电沉积只生成金属铜。     

Optical and electrochemical study of underpotential deposition of bismuth on gold electrode

The underpotential deposition of Bi on Au has been investigated by specular reflectance spectroscopy and linear sweep voltammetry. The spectral dependance of ΔR/R caused by Bi adatoms has been determined and compared with the calculated spectrum. A satisfactory agreement between experimental and calculated spectra was found. ΔR/R values have been used to determine the surface concentration of Bi_ad which then has been used to calculate the electrosorption valence of Bi_ad. It has been found that γ_Bi = 2.6. The optical evidence of interaction of Bi ions with gold oxide has been obtained.     

铜铝双金属复合离子液体的电化学行为及电沉积铜机理

铜铝双金属复合离子液体是新型碳四烷基化技术所用的绿色催化剂,电化学处理是回收工业应用过程外排复合离子液体中金属铜的有效途径之一,为此需要深入研究其电化学行为和电沉积铜机理。循环伏安研究发现,铜铝双金属复合离子液体在Pt盘电极、W盘电极和玻碳电极上的还原过程均包括铜的欠电势沉积、Cu(Ⅰ)的还原和铜的超电势沉积,氧化过程均包括Cu→Cu(Ⅰ)、Cu(Ⅰ)→Cu(Ⅱ)。计时安培研究表明,铜的成核方式为三维瞬时成核。长周期实验结果显示Cu(Ⅰ)的浓度随着时间下降的趋势变缓,表明电沉积铜速率逐步下降。电沉积电势对沉积产物的形貌影响较大,-2.60 V下的产物形貌更平整致密。XRD结果表明在-1.20~-2.60 V电势下阴极电沉积只生成金属铜。     

Selective growth of palladium and titanium dioxide nanostructures inside carbon nanotube membranes

ABSTRACT: Hybrid nanostructured arrays based on carbon nanotubes (CNT) and palladium or titanium dioxide materials have been synthesized using self-supported and silicon-supported anodized aluminum oxide (AAO) as nanoporous template. It is well demonstrated that carbon nanotubes can be grown using these membranes and hydrocarbon precursors that decompose at temperatures closer to 600°C without the use of a metal catalyst. In this process, carbonic fragments condensate to form stacked graphitic sheets, which adopt the shape of the pores, yielding from these moulds' multi-walled carbon nanotubes. After this process, the ends of the tubes remain open and accessible to other substances, whereas the outer walls are protected by the alumina. Taking advantage of this fact, we have performed the synthesis of palladium and titanium dioxide nanostructures selectively inside carbon nanotubes using these CNT-AAO membranes as nanoreactors.