Gold and Silver Micro‐Wire Electrodes for Trace Analysis of Metals

Micro‐wire electrodes were made from gold and silver wires (diameter: 25 μm; length: 3–21 mm) and sealed in a polyethylene holder; micro‐disk electrodes were made from the same wires and polished. The gold electrodes were electrochemically coated with mercury before use; the silver wires were used without coating. Comparative measurements demonstrated that the micro‐wire electrodes had much higher sensitivity, and a much (10–100×) lower limit of detection, than micro‐disk electrodes, and the sensitivity increased linearly with the area and length of the electrodes. Using a gold micro‐wire electrode of 21 mm and a deposition time of 300 s the limit of detection was 0.07 nM Pb in seawater of natural pH, compared to a limit of detection of 10 nM Pb (more than 100×greater) using a gold micro‐disk electrode of the same diameter. Using the silver micro‐wire electrode the limit of detection of lead was improved by a factor of 10 to 0.2 nM in acidified seawater. It is expected that the improved sensitivity of micro‐wire electrodes will lead to successful in situ detection of metals in natural waters.     

Electrochemical behavior of new electrode material: Compact of boron-doped synthetic diamond

Electrochemical properties of new electrode material—compact of boron-doped synthetic diamond—is studied for the first time. Cylindrical samples 3.5–4 mm in diameter and 2.5 mm in height were obtained by thermobaric processing of graphite–boron carbide mixtures in the diamond thermodynamic stability region (at the pressure of 8–9 GPa and temperature of ~2500 K). Their electrode behavior is studied using cyclic voltammetry and electrochemical impedance spectroscopy techniques. The cyclic voltammograms of the compact samples showed that their electrode characteristics are similar to those of traditional thin-film diamond electrodes obtained by the chemical vapor deposition (CVD) technique. In particular, they demonstrate rather wide potential window, low background current in indifferent electrolytes, and good reproducibility. It can be concluded that the diamond compacts practically are not inferior to the thin-film CVD-diamond electrodes and can serve as indicator electrodes, e.g., in electroanalysis. At the same time their compact form may be a convenience in the designing of electrolyzers and other electrochemical devices.     

聚苯胺的电化学现场ESR-电导同步测量

本论文工作通过设计新型的电解池 ,首次实现了导电聚合物的电化学现场ESR_电导同步测量 .从获得的聚苯胺ESR信号及膜电阻随电极电势变化的精细图象看出 ,极化子晶格的形成与消亡决定了聚苯胺的导电行为 .从不同电势下聚苯胺的ESR饱和行为也得到Curie自旋与Pauli自旋相互转化的新证据 .     

Scanning tunneling microscopy (STM) and scanning electron microscopy (SEM) of electrodispersed gold electrodes

Images of large active surface (electrodispersed) gold electrodes obtained by electroreduction of an oxide layer grown by applying a fast periodic square wave potential to polycrystalline specimens, have been obtained by STM and SEM. For the first time a correlation of imaging data of both microscopes can be established which allows one to find different structural details of these electrodes. The roughening increase produced by the electrochemical activation is explained tentatively through a generalized structural model consisting of an overlayer of sticking spheres of about 10 nm average diameter leaving inner interconnected channels of nearly the same average diameter and penetrating in the overlayer structure. The size of the spherical units is comparable to that of metal clusters involving the optimal ratio of surface to bulk atoms associated with the greatest catalytic activity.     

Magnetic field effects on the open circuit potential of ferromagnetic electrodes in corroding solutions

Magnetic fields shift the open circuit potential (OCP) of ferromagnetic electrodes (Fe, Co, and Ni) in corroding solutions. The OCP changes we observe (a) follow the series Fe>Co>Ni; (b) increase with the magnetic flux density; (c) reach a maximum with disk electrodes approximately 1 mm in diameter; and (d) depend on the orientation of the electrode. We report that when the surface of the electrode is oriented parallel (theta = 90 degrees) or perpendicular (theta = 0 degrees) to the magnetic field, the open circuit potential moves in opposite directions (positive and negative, respectively) with the largest changes occurring when the electrode surface is parallel to the magnetic field. Nonconvective sleeve electrodes produce the same behavior. The overall experimental evidence suggests that the magnetic field changes the OCP by modifying the surface concentrations of the paramagnetic participants in the corrosion process of the ferromagnetic electrode by species in solution; this in turn is accomplished by imposing a field-gradient driven mode of mass transfer upon paramagnetic species in solution (magnetophoresis). Simulations of the magnetic field around the ferromagnetic electrode at the two extreme orientations considered here show that in one case (theta = 90 degrees) field gradients actually repel, while in the other case (theta = 0 degrees) they attract paramagnetic species in the vicinity of the electrode.     

Water oxidation at hematite photoelectrodes: the role of surface states

Hematite (α-Fe(2)O(3)) constitutes one of the most promising semiconductor materials for the conversion of sunlight into chemical fuels by water splitting. Its inherent drawbacks related to the long penetration depth of light and poor charge carrier conductivity are being progressively overcome by employing nanostructuring strategies and improved catalysts. However, the physical-chemical mechanisms responsible for the photoelectrochemical performance of this material (J(V) response) are still poorly understood. In the present study we prepared thin film hematite electrodes by atomic layer deposition to study the photoelectrochemical properties of this material under water-splitting conditions. We employed impedance spectroscopy to determine the main steps involved in photocurrent production at different conditions of voltage, light intensity, and electrolyte pH. A general physical model is proposed, which includes the existence of a surface state at the semiconductor/liquid interface where holes accumulate. The strong correlation between the charging of this state with the charge transfer resistance and the photocurrent onset provides new evidence of the accumulation of holes in surface states at the semiconductor/electrolyte interface, which are responsible for water oxidation. The charging of this surface state under illumination is also related to the shift of the measured flat-band potential. These findings demonstrate the utility of impedance spectroscopy in investigations of hematite electrodes to provide key parameters of photoelectrodes with a relatively simple measurement.     

Dynamic diffuse double-layer model for the electrochemistry of nanometer-sized electrodes

A dynamic diffuse double-layer model is developed for describing the electrode/electrolyte interface bearing a redox reaction. It overcomes the dilemma of the traditional voltammetric theories based on the depletion layer and Frumkin's model for double-layer effects in predicating the voltammetric behavior of nanometer-sized electrodes. Starting from the Nernst-Planck equation, a dynamic interfacial concentration distribution is derived, which has a similar form to the Boltzmann distribution equation but contains the influence of current density. Incorporation of the dynamic concentration distribution into the Poisson and Butler-Volmer equations, respectively, produces a dynamic potential distribution equation containing the influence of current and a voltammetric equation containing the double-layer effects. Computation based on these two equations gives both the interfacial structure (potential and concentration profiles) and voltammetric behavior. The results show that the electrochemical interface at electrodes of nanometer scales is more like an electric-double-layer, whereas the interface at electrodes larger than 100 nm can be treated as a concentration depletion layer. The double-layer nature of the electrode/electrolyte interface of nanometer scale causes the voltammetric responses to vary with electrode size, reactant charge, the value of formal redox potential, and the dielectric properties of the compact double-layer. These voltammetric features are novel in comparison to the traditional voltammetric theory based on the transport of redox molecules in the depletion layer.     

Numerical simulation of the onset of mass transfer and convection in copper electrolysis subjected to a magnetic field

Numerical investigations have been performed in order to simulate the transient behaviour of copper electrolysis in a rectangular cell with vertical electrodes in a galvanostatic regime where the kinetics of the electrodes is controlled by charge-transfer. The transient behaviour observed for a binary electrolyte reproduces the temporal evolution of the concentration distribution measured in recent experimental work. Horizontal magnetic fields that vary linearly between the electrodes create Lorentz forces that either enhance or attenuate natural convection. The different time scales of natural convection and convection driven by the Lorentz force lead to interesting transient effects. The simulations performed for the case of an attenuating Lorentz force explain the dynamics of vertical inhomogeneities of the concentration boundary layer during the initial stages of electrolysis that were previously observed experimentally.     

Effect of the nanostructure on the CO poisoning rate of platinum

Platinum was electrochemically deposited in the forms of nanowires and nanotubes and compared to Pt black and Pt wire electrodes. The resistance to CO poisoning was measured in CO saturated solution by recording the current decrease in the H adsorption/desorption region through continuous sweeping of the electrode potential between 0.00 and 0.45 V vs RHE. For Pt deposits prepared with the same deposition charge, it is shown that the maximum coverage of CO, θ_CO,max, decreases as one goes from Pt black, to nanowires and to nanotubes. In the case of the longest nanotube prepared, θ_CO,max is as low as 0.44.     

Theory of porous electrodes: Calculation of overall cathode characteristics for the case where the polarization curve has segments with different slopes

It is demonstrated how one should carry on with calculations of overall currents and other parameters that characterize active layers of porous electrodes in the case where polarization curves for the catalyst display two or more segments with different slopes and exchange currents. A calculation of overall currents presumes that the active layer of an electrode has an optimum thickness, over which the current reaches a maximum. The entire range of values of the cathode potential is considered, specifically, the high potentials (from a steady-state potential up to the point where there is observed an inflection in the polarization curve), the intermediate potentials (near the front surface and near the rear surface of the active layer there are realized segments of the polarization curve with different slopes), and the low potentials (throughout the entire thickness of the active layer there is observed a second segment of the polarization curve). To give an example, calculations of overall characteristics of a cathode with Nafion and platinum are performed.     

Determination of the pore connectivity and pore size distribution and pore spatial distribution of porous chromatographic particles from nitrogen sorption measurements and pore network modelling theory

The pore connectivity, pore size distribution and pore spatial distribution of the porous structure of native and silanized silica particles were determined by matching the experimental nitrogen sorption data with the theoretical results obtained from pore network model simulations. The agreement between theory and experiment is found to be good. The results clearly indicate that the deposition of the silane layer to the pore surfaces of the native silica particles produces a silanized silica particle with a mean pore diameter and pore connectivity smaller than that of the native silica particle. Furthermore, the evaluation of the pore diffusivity of ribonuclease under unretained conditions shows that the lower values of the pore connectivity found in the samples of silanized silica particles, when compared with the values of the pore connectivity obtained for the native silica particles, increase the diffusional mass transfer resistance within the porous structure of the silanized silica particles.     

Ionic strength-controlled virtual area of mesoporous platinum electrode

Mesoporous electrodes provide an unusual opportunity to observe the dramatic transition of the electrochemical potential distribution in vicinity to mesoporous surfaces as the ionic strength varies. The experimental results were in accordance with what the classical Gouy-Chapman theory predicts on the basis of the correlation between Debye length (kappa-1) and the diameter of mesopores. Using the phenomenon that the electrochemically effective area of mesoporous electrode depends on the ionic strength, the faradaic current density of dioxygen reduction could be controlled by the electrolyte concentration.     

High transmission 3D printed flex‐PCB‐based ion funnel

In this study a novel fabrication method for a radio frequency (RF) ion funnel is presented. RF ion funnels are important devices for focusing ion clouds at low vacuum conditions for mass spectrometry or deposition‐related applications. Typically, ion funnels are constructed of stainless steel plate ring electrodes with a decreasing diameter where RF and direct current potentials are applied to the electrodes to focus the ion cloud. The presented novel design is based on a flexible circuit board that serves both as the signal distribution circuit and as the electrodes of the ion funnel. The flexible circuit board is rolled into a 3D printed scaffold to create a funnel shape with ring electrodes formed by the copper electrodes of the flexible circuit board. The design is characterized in direct comparison with a conventional steel‐plate electrode design. The discussed results show that the new funnel has similar performance to the conventionally designed funnel despite much lower manufacturing costs. Copyright © 2015 John Wiley & Sons, Ltd.     

Influence of fused deposition modeling parameters on the mechanical properties of ABS parts

This work aims to determine the influence of fused deposition modeling (FDM) printing parameters on the mechanical properties of parts fabricated on an Ultimaker2 printer with acrylonitrile butadiene styrene (ABS). The effect of several parameters such as interlayer cooling time (ILCT), nozzle diameter, infill density, raster angle and layer thickness on the ultimate tensile strength, yield strength, and elastic modulus of produced parts was evaluated. Two independent studies were conducted: a first study dedicated to the ILCT and a second study where the influence of other parameters was evaluated through a design of experiments (DoE) approach. Both studies were carried out through the execution of standard tensile tests. The statistical analysis of tensile tests results was processed with the ANOVA methodology. The obtained results indicate that a reduced ILCT improves the tensile strength of parts. It is shown that nozzle diameter and infill density are the parameters that most influence the mechanical properties of ABS, with the upper range selected values improving the studied mechanical properties. The raster angle configuration of (?45^o/45^o) benefits UTS and yield strength of ABS samples. Interactions of nozzle diameter on layer thickness were detected. It was observed that smaller layer thickness promotes a higher elastic modulus and UTS; however, for thinner layers (0.06‐0.10 mm), no significant differences were found on strength of samples due to potential high distortion levels.     

Polystyrene latex adsorption at the gold/electrolyte interface

Irreversible deposition of polystyrene latex particles (average diameter, 1.5 microm) on various solid/electrolyte interfaces was studied experimentally by using the direct microscope observation method. The substrate surfaces included bare mica (reference interface), gold covered mica (layer thickness of 50 nm), and solid gold plate. The morphology and thickness of the gold layer on mica was determined by atomic force microscopy. Well-defined transport conditions of particles were created by using the new impinging-jet cell. A characteristic feature of the cell was that the suspension stream was directed obliquely to the interface. This unique characteristic was advantageous allowing one for direct, in situ, observation of particle deposition at metals and other nontransparent interfaces. Experiments performed for various flow intensities indicated that the initial deposition kinetics at all interfaces was identical within the error bounds, in accordance with the model based on the convective-diffusion theory. It was concluded that the limiting flux was governed by the bulk transport rather than by the specific surface interactions.     

Recessed microelectrode array for a micro flow-through system allowing on-line multianalyte determination in vivo

Using CMOS-compatible processes, a microelectrode system for use in a micro flow-through cell was manufactured. The electrode was specially designed to enable multianalyte determination with immobilized oxidase enzymes and combines minimal flow dependency with a very small dead volume (< 1 μL) of the cell. This allows biomedical applications like measurements of glucose and lactate in interstitial fluid, which can be collected by ultrafiltration. Besides a 3-electrode system with 4 individually addressable platinum working electrodes, the sensor contains 2 electrodes that measure the conductivity of the sample as well as a Pt thermoresistor to measure the temperature. The temperature dependence in enzyme reactions can thus be controlled during on-line measurements. The 4 working electrodes comprise multielectrode arrays, each comprising 192 micro-holes with a diameter of 3.6 μm. They are arranged symmetrically around the central counter electrode, which is surrounded by a circular Ag/AgCl reference electrode. Between the array and the reference electrode are the loops of the Pt thermoresistor. The thermoresistor is electrically insulated from the measurement solution by a Si₃N₄ layer. A method for the pretreatment of platinum thin-film electrodes that increases the reversibility of the electrode process is described. The chemical modification of the working electrodes by electropolymerization of a resorcinol/1,3-diaminobenzene mixture enables interference-free measurement in blood and plasma as well as protection against electrode fouling.     

Electrokinetic Properties of Fuzzy Colloidal Particles

The presence of a thin polymer layer on the surface of a colloidal particle can have a profound effect on its electrophoretic mobility. The model developed here treats the hydrodynamics of the polymer layer as a distribution of Stokes resistance centers within a thin diffuse layer; fixed charge may reside on the surface of the particle core or throughout the layer. The theory is semianalytical in that asymptotic methods are used to simplify the equations but several integrals must be evaluated numerically. Special attention is paid to the effects of polarization and relaxation. It is shown that distributing immobile charge throughout the layer produces a response where the particle's mobility exceeds that found when the same amount of charge is spread uniformly over the surface of the rigid core. Increasing the drag due to the fuzzy layer always diminishes the mobility. In either case, the hydrodynamic permeability of the layer has a strong influence on particle movement. Results are also given for the dipole coefficient in the expression for the conductivity of a dilute suspension. Copyright 2000 Academic Press.     

Studies on interfacial electrochemical phenomena in pigment-vehicle systems

Sedimentation potentials under a centrifugal field are studied with the disperse system titanium dioxide, alkyd resin and xylene. The relationships between the sedimentation potential and the rotation speed, the distance apart of the electrodes in the cell and the total weight of particles in the disperse system are examined. From the theoretical evaluation of the initial sedimentation potential, the zeta potential of the pigment in the disperse system is calculated. The calculated value was almost coincident with that obtained by the electrophoretic method. As the sedimentation potential is proportional to the total weight of pigment in the space between the electrodes in the cell, the particle-size distribution of pigment can be obtained from the sedimentation potential-time curve. The particle-size distribution in the above-mentioned disperse system was examined with respect to the effect of rotation speed and the pigment content. The modal diameter for the particle-size distribution obtained by this method had almost the same value as that obtained by the electron microscope method. By use of this method for particle-size analysis, the particle-size distribution for particles of diameter < 1 mum can be obtained in a short time (ca, 10-30 min) and the zeta potential of the particles in the disperse system can be calculated.     

New solid-state glass electrodes by using zinc oxide thin films as interface layer

Novel glass electrodes for the determination of cations with reversible internal solid contact are introduced. They are based on a semiconducting zinc oxide layer with a maximum thickness of 1 μm in contact with ion selective glasses on one side and with a metal layer on the other side. The metal oxide layer is thereby generated either by ultrasonic spray pyrolysis from zinc acetate solution, by electrochemical deposition from zinc nitrate solution or by spin coating from a dispersion of ZnO in an organic binder. A following activation in a palladium chloride solution allows the chemical reductive deposition of NiP as electronic conductor. Dipping-type and flow through electrodes as well as planar glass electrodes in thick film technology fabricated in the above-mentioned method are described. In this case gold electrodes are applied by screen printing on isolated steel substrates. The zinc oxide layers, created in different manners, are covered afterwards with cation selective glasses in thick film technology. They cause a stabilisation of the half-cell potentials of the all solid state indicator electrodes proved by suitable measurements.