Electrochemical Impedance Spectroscopy Response Research Articles

Two parallel diffusion paths model for interpretation of PITT and EIS responses from non-uniform intercalation electrodes

Two alternative models, including (i) a serial combination of finite-space Warburg (FSW) and finite-length Warburg (FLW) elements, and (ii) two parallel FSW elements with different diffusion time constants, were proposed to describe the most important specific features of potentiostatic intermittent titration (PITT) and electrochemical impedance spectroscopy (EIS) responses of practical intercalation anodes and cathodes. Based on the physical reliability of the fitting parameters, the parallel diffusion path model was seen to describe adequately the EIS and PITT responses obtained from thin, non-uniform composite electrodes (graphite is considered as an example). Some important issues related to impedance modeling (exemplified by comparison of the properties of serial and parallel combinations of distributed diffusion elements) are discussed. We show that dlog|I d (t)|/ dlog t vs. t/ τ d plots are very useful for diagnosing the type of non-uniformity (particle size distribution, PSD) of intercalation electrodes.

Frequency Response Analysis of the Potential Modulated Microwave Reflectivity Response of p-Type Silicon During Anodic Dissolution in Ammonium Fluoride Solutions

Abstract Interpretation of the impedance of the silicon electrolyte interface is particularly complicated under conditions in which anodic silicon dissolution occurs. In the present work the frequency-resolved potential modulated microwave reflectivity (PMMR) technique has been combined with electrochemical impedance spectroscopy (EIS) to study the behaviour of low-doped p-type silicon in buffered ammonium fluoride. The EIS response is determined by the total impedance of the system, whereas the PMMR response originates from modulation of the hole density in the silicon space charge region. This difference has led to the development of a novel approach to deconvolution of the interfacial impedance. It involves multiplication of the PMMR and EIS responses to give the space charge impedance. Particular attention is focussed on accumulation conditions in the electropolishing region, where the surface of the silicon is covered by a duplex oxide film. The impedance of the accumulation layer is obtained using the new approach, and the oxide impedance is then derived. Analysis of the PMMR results provides convincing evidence that the hole mobility in the accumulation layer is more than an order of magnitude smaller than in the bulk.

The Effect of Heat Treatment on the Corrosion Resistance of 440C Stainless Steel in 20% HNO<SUB>3</SUB> + 2.5% Na<SUB>2</SUB>Cr<SUB>2</SUB>O<SUB>7</SUB> Solution

The effect of heat treatment on the corrosion resistance of 440C stainless steel was investigated in a 20% HNO3 + 2.5% Na2Cr2O7 solution using electrochemical noise (ECN) measurements, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) examinations. The noise resistance (Rn), which has been found to be inversely related to the localized corrosion rate, was measured to be 5.7E + 08 Ω-cm2, 4.2E + 08 Ω-cm2, and 3.7E + 04 Ω-cm2 for the oil-quenched, air-quenched, and vacuum furnace cooled (VFC) samples, respectively, after 1200 s exposures. The Rn for all heat treat conditions stabilized within a range of 1.0E + 07 Ω-cm2 to 3.2E + 08 Ω-cm2 after 2 h exposures. The EIS response showed a polarization resistance (R p) on the order of 6.6E + 04 Ω-cm2, 5.3E + 04 Ω-cm2, and 1.1E + 04 Ω-cm2 for the oil-quenched, air-quenched, and VFC samples, respectively, after 2 h exposures. The EIS data are in good agreement with ECN data and indicate that after longer exposures, general corrosion mechanisms dominate and the corrosion rates are comparable. SEM examinations of specimens subjected to 1200 s exposures revealed that severity of pitting and intergranular corrosion damage was consistent with trends in the Rn data. Specifically, the electrochemical noise data as well as SEM examinations of specimens revealed a higher localized corrosion resistance of the hardened specimens during the early stages of passivation. This greater resistance to localized corrosion can be attributed to an increased stability of the natural passive film resulting from a higher concentration of chromium atoms in solution for the martensite phase.

Evidence of a polymeric film formation from furfural electrooxidation on platinum platinized electrode in acetonitrile

A polymeric film formed from furfural (2‐furancarboxaldehyde) dissolved in acetonitrile was observed on Pt/Pt electrodes. Three different electrochemical methods such as cyclic voltammetry (CV), chronopotentiometry, and chronoamperometry were used to grow the film. The polymeric film was perfectly visible on the electrode surface, however, scanning electron microscopy (SEM) photographs were taken in order to confirm the presence of the film. The structure of the polymer according to the data obtained from IR spectroscopic data is also presented. The influence of the film on the electrochemical behavior of the platinum electrode was characterized by comparing the I(E) curves in aqueous 0.50 mol/L H2SO4 solutions. After recovering the voltammograms confirm the modification of the electrode surface. Basically, a strong inhibition of hydrogen reduction/oxidation was observed in the cathodic potential range. However, at potentials more positive than 1.10 V (SCE) the stability of the film was poor, suggesting a degradation of the polymer. The electrochemical impedance spectroscopy (EIS) responses of modified Pt/Pt electrodes coated with polyfurfural were also placed in aqueous sulfuric acid. The presence of the film on the electrode surface was characterized by a capacitive behavior at low frequencies.

Localized Impedance Measurements along a Single Channel of a Solid Polymer Fuel Cell

A method is presented, for the first time, for measuring the localized electrochemical impedance spectroscopy response over a frequency range of 0.1 Hz to 10 kHz as a function of position in a solid polymer fuel cell. The highly idealized fuel cell on which the measurements were performed is composed of a single linear flow channel. Measurements have been made at both 0.8 and 0.6 V. A distribution of impedance characteristics is seen along the channel with evidence of mass transport effects that are not evident from localized dc measurements. The membrane conductivity does not vary with position at both potentials, as is expected from the fact that reactant gases are fully humidified. A time constant characteristic of convective transport within the flow channel dominates the low frequency response at low potentials. This response is caused by consumption of reactant upstream of the point at which the measurement is made. © 2003 The Electrochemical Society. All rights reserved.

Electrochemical Impedance Spectroscopy and Its Applications to Lithium Ion Cells

AbstractFor Abstract see ChemInform Abstract in Full Text.

Reaction kinetics of amorphous Mg50Ni50 hydride electrode

Mg-based alloy is a promising hydride electrode material. In this study, the kinetics of the electrode reaction of an amorphous Mg50Ni50 hydride electrode is studied by using electrochemical impedance spectroscopy (EIS) technique. An equivalent circuit for the hydride electrode reaction is proposed. Results show that the reaction rate of the hydride electrode is determined by a charge-transfer reaction at the alloy surface, which is represented by the EIS responses in the medium frequency region. The serious corrosion of the active material on the alloy surface is the main reason for the high charge-transfer resistance of the electrode reaction.

A mixed-conduction model for oxide films on Fe, Cr and Fe–Cr alloys in high-temperature aqueous electrolytes––I. Comparison of the electrochemical behaviour at room temperature and at 200 °C

The aim of this two-part work is to propose a model for the corrosion mechanism of ferrous alloys in high-temperature aqueous environments. In the first part of the work, experimental results of the electrochemical behaviour of pure Fe, pure Cr, Fe–12%Cr alloy and Fe–25%Cr alloy during the initial stage of oxide film formation at 200 °C are compared to those obtained at room temperature. The results have been obtained by using voltammetry, electrochemical impedance spectroscopy (EIS), contact electric resistance (CER) and contact electric impedance (CEI) techniques. An increase of temperature from room temperature up to 200 °C has been found to result in higher currents in the passive region for all the materials. The CER, EIS and CEI results indicate that the film especially on Fe is considerably thicker at the higher temperature. In addition, the EIS and CEI results give information of an ionic transport process at 200 °C, which has not been observed in the EIS response at room temperature. The dependence of the electrical and transport properties of the film on potential suggests that the films at 200 °C can also be described by a mixed-conduction model (MCM) introduced recently for room temperature. However, the faster rate of ionic defect transport has to be emphasised at the higher temperature. The adaptation of the MCM to high-temperature oxide films is discussed in more detail in the second part of this work.

Electrochemical Impedance Spectroscopy Study of the Response Mechanism of the Jalpaite CuIIIon-Selective Electrode in Seawater

This paper presents the results of a novel study into the response mechanism of the jalpaite copper(II) ion-selective electrode (ISE) using electrochemical impedance spectroscopy (EIS) under conditions of minimal overpotential stimulation (i.e., ±10 mV). The EIS spectra of the jalpaite ISE in seawater and other ionic media revealed a high-frequency surface film impedance that is attributable to the modified hydrated surface layers of the ISE, and a low-frequency charge-transfer impedance that can be ascribed to the reductive ion-exchange of CuII at the membrane/electrolyte interface. EIS data for a rotating disk electrode have shown that the charge-transfer process is under diffusion control. EIS and potentiometric response data in UV-oxidized seawater spiked with humic acid imply that organic complexation of CuI at the electrode diffusion layer is responsible for a weak interference effect. The classical chloride interference effect of the jalpaite CuII ISE occurring at high concentrations of CuII (i.e.,...

Active dissolution mechanisms of iron using EIS with channel flow double electrode. Influences of chloride and fluoride ions

The active dissolution mechanism of iron in acidic solutions containing halide ions was investigated by electrochemical impedance spectroscopy (EIS) with channel flow double electrode (CFDE). CFDE is a hydrodynamic technique similar in principle to the rotating ring disc electrode (RRDE). A dissolution efficiency Φ diss of the iron electrode in the frequency domain was obtained using the dynamic collection efficiency N( ω). By the addition of NaCl and NaF in sulfuric acid solution (pH 1), Nyquist plot of the electrochemical impedance Z showed a capacitive semicircle and apparently two inductive semicircles, and that of Φ diss showed two semicircles. These experimental results indicate that ferrous ions dissolve through two dissolution paths in the presence of chloride ions, ie, reaction paths through a FeOH adsorbed intermediate and through a FeCl adsorbed intermediate. In order to investigate the role of chloride ions, numerical simulations for EIS responses and polarization curves were performed on the basis of the above reaction model, assuming the two dissolution paths, and simulated results were in good agreement with the experimental results.

AC Impedance Studies on Metal Hydride Electrodes

The metal hydride electrode is the negative electrode in one of the most advanced secondary batteries (i.e., nickel/metal hydride). The objective of this study is to obtain insight on the mechanism of the hydriding/dehydriding reaction in the battery by using the electrochemical impedance spectroscopy (EIS) technique. An equivalent circuit for the electrode reaction is proposed. The rate capability of charge and discharge of the electrode is determined by the kinetics of the charge‐transfer reaction at the alloy surface, which is mainly represented by the EIS responses in the low frequency region. Transient and pseudo‐steady‐state analyses (cyclic voltammetry and potential vs. current density behavior) qualitatively and quantitatively support the EIS results. EIS studies on electrodes with (i) three types of binding additives, (ii) varying amounts of active material, and (iii) two types of alloys as active materials demonstrate the usefulness of this technique for developing electrodes with the optimum composition and structure.

The Platinum Microelectrode/Nafion Interface: An Electrochemical Impedance Spectroscopic Analysis of Oxygen Reduction Kinetics and Nafion Characteristics

The kinetics of oxygen reduction at the platinum/proton‐exchange‐membrane interface is of direct importance in solid‐polymer‐electrolyte fuel‐cell research and development. Previous studies at a platinum microelectrode/Nafion® interface yielded electrode‐kinetic parameters for this reaction. The objectives of this study were to use electrochemical impedance spectroscopy (EIS) to study the oxygen‐reduction reaction under lower humidification conditions than previously studied. The EIS technique permits the discrimination of electrode kinetics of oxygen reduction, mass transport of in the membrane, and the electrical characteristics of the membrane. Electrode‐kinetic parameters for the oxygen‐reduction reaction, corrosion current densities for Pt, and double‐layer capacitances were calculated. The production of water due to electrochemical reduction of oxygen greatly influenced the EIS response and the electrode kinetics at the Pt/Nafion interface. From the finite‐length Warburg behavior, a measure of the diffusion coefficient of oxygen in Nafion and diffusion‐layer thickness was obtained. An analysis of the EIS data in the high‐frequency domain yielded membrane and interfacial characteristics such as ionic conductivity of the membrane, membrane grain‐boundary capacitance and resistance, and the uncompensated resistance.