21 research outputs found
Resolution of a multi-step electron transfer reaction by time resolved impedance measurements: Sulfur reduction in nonaqueous media
No full textThe first reduction peak of the cyclic voltammograrn (CV) for sulfur reduction in dimethyl sulfoxide has been studied using time resolved Fourier transform electrochemical impedance spectroscopic (FTEIS) analysis of small potential step chronoamperometric currents. The FTEIS analysis results reveal that the impedance signals obtained during short potential steps can be resolved into electron transfer reactions of two different time constants in a high frequency region. The FTEIS method provides snap shots of impedance profiles during an earlier phase of the reaction, leading to time resolved EIS measurements. Our results obtained by the FTEIS analysis are consistent with a series of electron transfer and chemical equilibrium steps of a complex reaction, making up an ECE (electrochemical-chemical-electrochemical) mechanism postulated from the results of computer simulation.X1111sciescopuskc
Feasibility of Applying Fourier Transform Electrochemical Impedance Spectroscopy in Fast Cyclic Square Wave Voltammetry for the <i>In Vivo</i> Measurement of Neurotransmitters
No full textWe
previously reported on the use of fast cyclic square wave voltammetry
(FCSWV) as a new voltammetric technique. Fourier transform electrochemical
impedance spectroscopy (FTEIS) has recently been utilized to provide
information that enables a detailed analytical description of an electrified
interface. In this study, we report on attempts to combine FTEIS with
FCSWV (FTEIS–FCSWV) and demonstrate the feasibility of FTEIS–FCSWV
in the in vivo detection of neurotransmitters, thus
giving a new type of electrochemical impedance information such as
biofouling on the electrode surface. From FTEIS–FCSWV, three
new equivalent circuit element voltammograms, consisting of charge-transfer
resistance (Rct), solution-resistance
(Rs), and double-layer capacitance (Cdl) voltammograms were constructed and investigated
in the phasic changes in dopamine (DA) concentrations. As a result,
all Rct, Rs, and Cdl voltammograms showed different
DA redox patterns and linear trends for the DA concentration (R2 > 0.99). Furthermore, the Rct voltammogram in FTEIS–FCSWV showed lower limit
of detection (21.6 ± 15.8 nM) than FSCV (35.8 ± 17.4 nM).
FTEIS–FCSWV also showed significantly lower prediction errors
than FSCV in selectivity evaluations of unknown mixtures of catecholamines.
Finally, Cdl from FTEIS–FCSWV showed
a significant relationship with fouling effect on the electrode surface
by showing decreased DA sensitivity in both flow injection analysis
experiment (r = 0.986) and in vivo experiments. Overall, this study demonstrates the feasibility of
FTEIS–FCSWV, which could offer a new type of neurochemical
spectroscopic information concerning electrochemical monitoring of
neurotransmitters in the brain, and the ability to estimate the degree
of sensitivity loss caused by biofouling on the electrode surface
Development of Galvanostatic Fourier Transform Electrochemical Impedance Spectroscopy
No full textHere, we report development of the galvanostatic Fourier transform electrochemical impedance spectroscopy (FTEIS), which monitors impedance of electrochemical reactions activated by current steps. We first derive relevant relations for potential change upon application of a step current, obtain impedances theoretically from the relations by simulation, and verify them with experimental results. The validity of the galvanostatic FTEIS technique is demonstrated by measuring impedances of a semiconductive silicon wafer using the conventional frequency response analysis (FRA), the potentiostatic FTEIS, and the galvanostatic FTEIS methods, and the results are in excellent agreement with each other. This work is significant in that the galvanostatic FTEIS would allow one to record impedance changes during charge/discharge cycles of secondary batteries and fuel cells as well as electrochemically irreversible systems which may produce noise level chronoamperometric currents by potentiostatic techniques.close
Development of Galvanostatic Fourier Transform Electrochemical Impedance Spectroscopy
No full textHere, we report development of the galvanostatic Fourier transform electrochemical impedance spectroscopy (FTEIS), which monitors impedance of electrochemical reactions activated by current steps. We first derive relevant relations for potential change upon application of a step current, obtain impedances theoretically from the relations by simulation, and verify them with experimental results. The validity of the galvanostatic FTEIS technique is demonstrated by measuring impedances of a semiconductive silicon wafer using the conventional frequency response analysis (FRA), the potentiostatic FTEIS, and the galvanostatic FTEIS methods, and the results are in excellent agreement with each other. This work is significant in that the galvanostatic FTEIS would allow one to record impedance changes during charge/discharge cycles of secondary batteries and fuel cells as well as electrochemically irreversible systems which may produce noise level chronoamperometric currents by potentiostatic techniques.X11119sciescopu
Development of Galvanostatic Fourier Transform Electrochemical Impedance Spectroscopy
No full textHere, we report development of the galvanostatic Fourier
transform
electrochemical impedance spectroscopy (FTEIS), which monitors impedance
of electrochemical reactions activated by current steps. We first
derive relevant relations for potential change upon application of
a step current, obtain impedances theoretically from the relations
by simulation, and verify them with experimental results. The validity
of the galvanostatic FTEIS technique is demonstrated by measuring
impedances of a semiconductive silicon wafer using the conventional
frequency response analysis (FRA), the potentiostatic FTEIS, and the
galvanostatic FTEIS methods, and the results are in excellent agreement
with each other. This work is significant in that the galvanostatic
FTEIS would allow one to record impedance changes during charge/discharge
cycles of secondary batteries and fuel cells as well as electrochemically
irreversible systems which may produce noise level chronoamperometric
currents by potentiostatic techniques
Zinc Oxidation in Dilute Alkaline Solutions Studied by Real-Time Electrochemical Impedance Spectroscopy
No full textElectrochemical oxidation of zinc has been studied in dilute alkaline solutions, 0.010 and 0.10 M KOH, employing cyclic voltammetric and real-time Fourier transform electrochemical :Impedance spectroscopy (FTEIS) experiments. Thermodynamic analysis of cyclic voltammetric data indicates that Zn(OH)(4)(2-) is produced as a major product in both 0.10 and 0.010 M KOH although ZnO/Zn(OH)(2) may also be produced as a minor product in 0.010 M. A large body of impedance data was obtained as a function of swept potential by running combined staircase cyclic voltammetry and FTEIS (SCV-FTEIS) experiments at every 10 mV and 200 ms interval, which allowed a systematic and complete analysis to be made on the interface. Analysis of the extensive impedance data demonstrates that electron transfer takes place across the thin oxide/hydroxide film, whose electrical state undergoes drastic changes at the potential where charge transfer occurs. The capacitance of the film covering the surface was shown to undergo a large change during the charge transfer indicating that the electrode/electrolyte interface is strongly electrified during the charge transfer across it. Various electrode reaction kinetic parameters for oxidation of zinc are also reported by treating the impedance data and the reaction mechanism is discussed based on the data.close101
Fourier transform electrochemical impedance spectroscopic studies on anodic reaction of lead
No full textLead oxidation and subsequent oxygen evolution have been studied in a zinc electrowinning solution employing cyclic voltammetric and real-time Fourier transform electrochemical impedance spectroscopy (FTEIS) experiments. A large body of impedance data obtained as a function of scanned potential by running combined staircase cyclic voltammetry and FTEIS experiments led to systematic analysis on the electrode/electrolyte interface. The changes in solution resistances, film resistances as well as film capacitances, double layer capacitances, polarization resistances, and Warburg admittances observed during lead oxidation satisfactorily explain corresponding electrochemical reactions. Various electrode reaction kinetic parameters for oxidation of lead and oxygen evolution were obtained from the impedance data. The reaction mechanism is discussed based on the impedance data.close
Electrochemistry of conductive polymers 40. Earlier phases of aniline polymerization studied by fourier transform electrochemical impedance spectroscopy
No full textEarlier stages of aniline polymerization have been studied by Fourier transform electrochemical impedance spectroscopy (FTEIS) experiments. Initial oxidation of aniline leads to the formation of a thin layer passivating the electrode surface, which is depassivated upon a further increase in potential and mediates a further electron transfer from aniline to the electrode. The charge-transfer resistance was first shown to decrease upon increasing the potential, which leads to the inductive behavior upon further increase in the overpotential. The oligomer-polymer film thus formed was shown to undergo a transition from its passive state to neutral oligomer-polymer molecules via a conducting state; its oxidation was then observed during the anodic scan. It is this transition to the conductive states that leads to the propagation of the conductive zone throughout the nonconductive film, leading to further growth of polyaniline, as was clearly shown by the FTEIS measurements.X112323sciescopu
Fourier transform analysis of chronoamperometric currents obtained during staircase voltammetric experiments
No full textWe report a novel comprehensive Fourier transform electrochemical impedance spectroscopic (FTEIS) analysis method of a series of chronoamperometric currents obtained during staircase cyclic voltammetric (SCV) experiments. In our method, FTEIS analysis of a set of chronoamperometric currents recorded upon applying a series of small potential steps during an SCV experiment provides a complete description of an electron-transfer reaction at the electrode/electrolyte interface in forms of equivalent circuit elements. Conversion of the circuit elements thus obtained from the analysis allows electrode kinetic parameters including the electron-transfer rate constant, transfer coefficient, diffusion coefficient, and double layer capacitance as well as thermodynamic parameters such as the half-wave potential and the apparent number of electrons transferred to be determined. Theories for obtaining an ac admittance voltammogram, as well as both the thermodynamic and mass-transfer kinetic parameters thereof, from the SCV data have been developed and verified. A decided advantage of the method is that it provides completely self-contained information regarding an electron-transfer reaction from a single pass of the SCV experiment.X113332sciescopu
Electrochemical behavior of PbO2 nanowires array anodes in a zinc electrowinning solution
No full textFree-standing PbO2 nanowires were prepared by an electrodeposition process onto the titanium foil. The morphology of nanowires was investigated by SEM analyses. The contact angle of the nanowires was compared with that of planar film, which indicated higher hydrophilicity and surface energy of nanowires. Cyclic voltammetric and real-time Fourier transform electrochemical impedance spectroscopy (FTEIS) experiments were employed to study the anodic reaction on the surface. The cyclic voltammetric data showed the overpotential of nanowire array electrode decreased by more than 100 mV compared to that of the planar film electrode at an anodic current density of 400 A/m2. A large body of impedance data acquired from the two electrodes as a function of scanned potential by running combined staircase cyclic voltammetry and FTEIS experiments led to systematic comparative analysis on the electrode/electrolyte interface. The changes in solution resistances, film resistances and capacitances, double layer capacitances, and polarization resistances observed during oxygen evolution process were compared and explained by corresponding electrochemical reactions. The nanowires of PbO2 showed a large active surface area led to higher capacitance than that of the planar electrode.close2
