Search

Total-reflection X-ray absorption fine structure (TR-XAFS) technique was applied for the first time to an interface between two immiscible electrolyte solutions under potentiostatic control. The hydration structure of bromide ions was investigated at polarized 2-octanone/water interfaces. TR-XAFS spectra at Br K-edge measured in the presence of hexyltrimethylammonium bromide (C6TAB) were slightly modified depending on the Galvani potential difference (Δowϕ). The extended X-ray absorption fine structure analysis exposed hydration structure changes of bromide ions at the polarized interface. The coordination structure of bromide ions at the interface could be analyzed as compared with bromide ions dissolved in aqueous solution and Br−-exchanged resin having quaternary ammonium groups. The results indicated that bromide ions were associated with C6TA+ at the polarized interface. The relative contribution of ion association form of bromide ions with quaternary ammonium groups was enhanced at a potential close to the ion transfer of C6TA+, where the interfacial concentration of C6TA+ is increased as a function of Δowϕ. [ABSTRACT FROM AUTHOR]

The effect of reversible electrochemical reaction on Li diffusion and stress in a cylindrical Li-ion battery electrode is studied. A new relation among Li concentration, the fraction of forward reaction product, and the diffusion-reaction-induced stress is derived. The electrochemical reaction has little effect on Li diffusion but enhances the stress significantly, and the reaction induced stress is much larger than diffusion induced stress. The electrochemical reaction will accelerate structural fading or capacity loss of the electrode. The backward reaction can be ignored for both galvanostatic and potentiostatic charging but has a significant effect on stress for galvanostatic discharging. The optimized charging procedure considering the reversible electrochemical reaction is galvanostatic first followed by potentiostatic, which is consistent with the manufacturer recommendation procedure. [ABSTRACT FROM AUTHOR]

The UV-vis and the IR spectra of derivativized adenosine in dichloromethane have been recorded during potentiostatic oxidation at an optically transparent thin layer electrode. Oxidized adenosine shows a broad Zundel like absorption extending from 2800 up to 3600 cm-1, indicating that a proton transfer process is occurring. Theoretical computations predict that proton transfer is indeed favored in oxidized 1:1 self-association complexes and allow to assign all the observed transient spectroscopic signals. [ABSTRACT FROM AUTHOR]

This paper presents the design of a wireless portable and multichannel potentiostat for remote monitoring in enclosed environments for long-time applications. In this paper, the proposed potentiostat is tested for monitoring the glucose concentration during the fermentation of yeast in real time for more than 24 h. The potentiostat is powered by a USB-connected battery and operated through a Bluetooth using a LabVIEW designed data monitoring and control panel. The potentiostat is capable of performing cyclic voltammetry or chronoamperometry on six biosensors simultaneously and gives the real-time response using Bluetooth connection. The potentiostat has a common counter electrode and reference electrode connection to all biosensors and independent working electrodes for all biosensors. The potentiostat was tested and validated by comparing the results obtained by a commercial potentiostat. The tests performed for monitoring the glucose concentration during the fermentation process showed a current detection limit of 180 nA and reported a standard deviation of ±2% for anodic and cathodic current peaks for cyclic voltammetry measurements when compared with the commercially available device. This study enables the novel method of monitoring the fermentation process wirelessly for days. [ABSTRACT FROM AUTHOR]

The Fukui functions based on the computable local polarizability vector have been presented for a group of simple molecules. The necessary approximation for the density functional theory softness kernel has been supported by a theoretical analysis unifying and generalizing early concepts produced by the several authors. The exact relation between local polarizability vector and the derivative of the nonlocal part of the electronic potential over the electric field has been demonstrated. The resulting Fukui functions are unique and represent a reasonable refinement when compared to the classical ones that are calculated as the finite difference of the density in molecular ions. The new Fukui functions are strongly validated by their direct link to electron dipole polarizabilities that are reported experimentally and by other computational methods. [ABSTRACT FROM AUTHOR]

We have recently reported a hybrid conducting polymer-solid electrolyte heterojunction in which electronic channel current is controlled by ionic diffusion and redox reactions involving doped polyethyleneoxide and doped polyaniline (PANI). In this paper we demonstrate on the microscopic level the validity of the model we proposed to interpret the electronic behavior of the device we fabricated. In particular, we used resonance and vicinity (surface-enhanced-Raman-scattering like) enhanced micro-Raman spectroscopy to map out the redox state of PANI along the conducting channel, simultaneously with the determination of the voltamperometric characteristics in a potentiostat configuration. The Raman data were complemented as appropriate by the optical and Fourier transform infrared absorption spectroscopies. [ABSTRACT FROM AUTHOR]

The issue of the allowed sign of the differential capacity C of electrochemical interfaces has a long history dating back to the so-called ‘‘Cooper–Harrison catastrophe.’’ Previously suggested ‘‘electromechanical models’’ are modified to include entropic contributions; the possibility of C<0 for an isolated electric cell is supported by rigorous solution of the model. We also provide new evidence that for an electric cell in contact with a potentiostat (‘‘extended system’’) the overall C of the cell must be positive; the contribution of an individual double layer may still be negative. The previous statistical mechanical derivation of the upper boundary for C-1 is generalized for a quite general model of an electrolyte in contact with hard charged walls. We also discuss the possibility of electric instabilities and phase transitions in an extended system when an isolated prototype possesses a negative capacity branch. [ABSTRACT FROM AUTHOR]

This work reports the design and construction of a novel potentiostat which features an integrator transimpedance amplifier as a current-monitoring unit. The integration approach addresses the limitations of the feedback resistor approach used for current monitoring in conventional potentiostat designs. In the present design, measurement of the current is performed by a precision switched integrator transimpedance amplifier operated in the dual sampling mode which enables sub-pA resolution. The potentiostat is suitable for measuring very low currents (typical dynamic range: 5 pA-4.7 μA) with a 16 bit resolution, and it can support 2-, 3- and 4-electrode cell configurations. Its operation was assessed by using it as a detection module in a home-made capillary electrophoresis system for the separation and amperometric detection of paracetamol and p-aminophenol at a 3-electrode microfluidic chip. The potential and limitations of the proposed potentiostat to implement fast potential-scan voltammetric techniques were demonstrated for the case of cyclic voltammetry. [ABSTRACT FROM AUTHOR]

The article evaluates several scientific instruments and apparatus, including a femtosecond fiber laser from Calmar Laser Inc., the JSM-IT100 scanning electron microscope from JEOL USA Inc. and the Interface 5000 potentiostat from Gamry Instruments.

Combinatorial approaches for targeted discovery of new materials require rapid screening systems to evaluate large numbers of new material compositions. High-throughput combinatorial materials discovery is a capital-intensive undertaking requiring sophisticated robotic sample preparation and rapid screening assays. A distributed approach to combinatorial materials discovery can achieve similar goals by increasing the breadth of participation and reducing the size of the capital investment. The discovery of new photoactive materials for solar fuels production demands a screening device to probe materials for electrochemical current production upon irradiation with visible light. We have developed a system that uses an array of pulsed light-emitting diodes (LEDs) synchronized with a two-electrode potentiostat that can measure the photoelectrochemical responses of combinatorial sample arrays deposited on conducting glass plates. Compared to raster scanning methods, this LED system trades spatial resolution for a substantial reduction in scan time. [ABSTRACT FROM AUTHOR]

An impedance measurement system with probe signal frequencies up to 50 kHz with AC-probe voltages below 30 mV rms was integrated for wireless and battery-free monitoring of microbiological cell cultures. The here presented modular design and the use of state-of-the-art components greatly eases adoptions to a wide range of biotechnological applications without the need of bulky LCR-meters or potentiostats. The device had a power consumption of less than 2.5 mA at a 3.3 V single power supply and worked trouble-free within the humid environment of a cell culture incubator. Measurements on lumped RC-elements showed an error of less than 1% for absolute values and less than 1° regarding the phase of the complex impedance. The performance of sensor devices with interdigitated electrode structures for the measurement of adherent cell cultures was tested in the presence of phosphate-buffered saline solution in the humid atmosphere of an incubator for biological cell cultures. [ABSTRACT FROM AUTHOR]

This article presents a low-cost portable electrochemical instrument capable of on-site identification of heavy metals. The instrument acquires metal-specific voltage and current signals by the application of differential pulse anodic stripping voltammetry. This technique enhances the analytical current and rejects the background current, resulting in a higher signal-to-noise ratio for a better detection limit. The identification of heavy metals is based on an intelligent machine-based method using a multilayer perceptron neural network consisting of three layers of neurons. The neural network is implemented using a 16 bit microcontroller. The system is developed for use in the field in order to avoid expensive and time-consuming procedures and can be used in a variety of situations to help environmental assessment and control. [ABSTRACT FROM AUTHOR]

An experimental procedure intended for crevice corrosion studies on Ni–Cr–Mo alloys is demonstrated. In this procedure a potentiostatic control of crevice corrosion specimens is applied to an immersible crevice cell design that uses a fluoroelastomer gasket crevice former. The procedure is demonstrated for a crevice susceptibility study on Alloy 625 in elevated temperature natural seawater, where crevice corrosion initiation and propagation are shown to be influenced by the electrochemical potential. Potentiostatic current monitoring establishes the crevice initiation time and rate of propagation, while post-mortem inspections confirm the extent of crevice damage. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a method for the measurement of differential capacity in electrochemistry. Principles behind the potentiostatic method; Details of the antagonistic conditions that should be present in a potentiostatic control system; Characterization of potentiostat and galvanostat.

A general purpose multiple electrode potentiostat is described which allows the execution of novel electrochemical experiments. The potentiostat independently controls the potentials and measures the currents at multiple (up to eleven) working electrodes using a single auxiliary electrode and a single reference electrode. It is designed for either stand-alone operation or performance under the direction ora computerized data-acquisition and control system, and it is capable of implementing either stepped potential or scanned potential programs. A modular design consisting of a backplane data and control bus with slots for each independent component provides the means for relatively simple maintenance and facile expansion for arrangements employing additional working electrodes. Current sensitivities of 1 mA/V to 100 nA/V in five ranges are selectable with additional sensitivities of 10 nA/V, 1 nA/V, and 100 pA/V available through the use of a preamplifier. [ABSTRACT FROM AUTHOR]

Potentiostatic circuit configurations with work electrodes and auxiliary electrodes at ground potential have been reviewed and compared. Though the former is by far the best known and most used, the latter was more convenient and accurate in interfacial capacity measurements. [ABSTRACT FROM AUTHOR]

We describe a simple and inexpensive potentiostat, incorporating current boosting and filtering circuitry for use in the study of coloration and bleaching in eleetrochromic thin films. The system is sufficiently flexible to permit utilization in other electrochemical applications. [ABSTRACT FROM AUTHOR]

An electronic interface connecting the potentiostat of an electrochemical measurement system to a Fourier transform infrared (FTIR) spectrometer as used for in situ IR reflection absorption studies is described. It makes use of readily available components, is installed without any changes in the hardware of the spectrometer or the potentiostat, and allows fast and reliable spectroelectrochemical measurements. [ABSTRACT FROM AUTHOR]

High throughput electrochemical techniques are widely applied in material discovery and optimization. For many applications, the most desirable electrochemical characterization requires a three-electrode cell under potentiostat control. In high throughput screening, a material library is explored by either employing an array of such cells, or rastering a single cell over the library. To attain this latter capability with unprecedented throughput, we have developed a highly integrated, compact scanning droplet cell that is optimized for rapid electrochemical and photoeletrochemical measurements. Using this cell, we screened a quaternary oxide library as (photo)electrocatalysts for the oxygen evolution (water splitting) reaction. High quality electrochemical measurements were carried out and key electrocatalytic properties were identified for each of 5456 samples with a throughput of 4 s per sample. [ABSTRACT FROM AUTHOR]

We studied the control of the bandgap energy of graphene by doping manganese oxide nanoparticles using an electrochemical method. The manganese oxide doping into the graphene was a main role for the bandgap opening and the defect generation was an effective method to increase the density of Mn doping on the graphene. The measured bandgap increased and finally saturated at 0.256 eV as the concentration of manganese oxide nanoparticles increased. The bandgap energies were 0.22, 0.244, 0.250, and 0.256 eV at the applied voltage of 0.5, 1.0, 1.5, and 2.0 V, respectively. In addition, the defect generation by the plasma treatment resulted in improved formations of the bandgap energy up to 0.4 eV. The combination of the manganese oxide doping and the defect generation can enhance the bandgap energy effectively in the graphene. It is considered that the electrochemical doping technique is an effective way to control the bandgap energy of graphene. [ABSTRACT FROM AUTHOR]

A PET computer is used to control an electrochemical system incorporating a three-electrode potentiostat. [ABSTRACT FROM AUTHOR]