Electrochemical impedance spectra EIS

Wagner N, Gulzow E (2004) Change of electrochemical impedance spectra (EIS) with time during CO-poisoning of the Pt-anode in a membrane fuel cell. J Power Sources 127 341-7... 

Figure 6.31. Nyquist plots of the interpolated impedance spectra measured at 700 mV and different times during the progressive poisoning of the anode with CO [33], (Reprinted from Journal of Power Sources, 127(1-2), Wagner N, Gulzow E. Change of electrochemical impedance spectra (EIS) with time during CO-poisoning of the Pt-anode in a membrane fuel cell, 341-7, 2004, with permission from Elsevier and the authors.)...

Electrochemical Impedance Spectra EIS and Equivalent Circuit Diagram A... 

Schnumberger [1999] Change of Electrochemical Impedance Spectra (EIS) with Tune during CO-Poisoning of the Pt-Anode in a Membrane Fuel Cell, in Proton Conducting Membrane Fuel Cells II, ed. S. Gottesfeld and T. F. Fuller, Electrochem. Soc. Proc. 98-27,... 

More detailed information can be obtained from noise data analyzed in the frequency domain. Both -> Fourier transformation (FFT) and the Maximum Entropy Method (MEM) have been used to obtain the power spectral density (PSD) of the current and potential noise data [iv]. An advantage of the MEM is that it gives smooth curves, rather than the noisy spectra obtained with the Fourier transform. Taking the square root of the ratio of the PSD of the potential noise to that of the current noise generates the noise impedance spectrum, ZN(f), equivalent to the impedance spectrum obtained by conventional - electrochemical impedance spectroscopy (EIS) for the same frequency bandwidth. The noise impedance can be interpreted using methods common to EIS. A critical comparison of the FFT and MEM methods has been published [iv]. 

To determine numerical values for the different elements of the equivalent circuit they have to be separated, for example, by electrochemical impedance spectroscopy (EIS). Similar to the above-described lock-in measurement a small ac signal of a few mV is superimposed to the electrode potential. The resulting current and its phase shift are then measured as a function of the frequency. Typical impedance spectra of thin oxide films on aluminum are shown in Fig. 17. At high frequencies (10 — lO Hz) the capacitors act as shorts and only the electrolyte resistor determines the impedance, which is typically 10 Ohm for concentrated electrolytes and independent of the electrode. At the lowest frequencies, for example, 10 Hz or below, current flow through the capacitors is impossible and the impedance of the system is given by the sum of the 3 resistors in the current path. The... 

Electric Double Layer and Fractal Structure of Surface Electrochemical impedance spectroscopy (EIS) in a sufficiently broad frequency range is a method well suited for the determination of equilibrium and kinetic parameters (faradaic or non-faradaic) at a given applied potential. The main difficulty in the analysis of impedance spectra of solid electrodes is the frequency dispersion of the impedance values, referred to the constant phase or fractal behavior and modeled in the equivalent circuit by the so-called constant phase element (CPE) [5,15,16, 22, 35, 36]. The frequency dependence is usually attributed to the geometrical nonuniformity and the roughness of PC surfaces having fractal nature with so-called selfsimilarity or self-affinity of the structure resulting in an unusual fractal dimension... 

Electrochemical impedance spectroscopy (EIS) provides indirect information about the surface phenomena of all kinds of electrodes [32]. The high-frequency part of impedance spectra of electrodes is usually attributed to surface phenomena such as Li-ion migration through surface films, surface film capacitance, and interfacial charge transfer [33]. However, it should be noted that EES provides very ambiguous information. A special skill, as well as experience, is needed for a reliable assignment of spectral features to the time constants of a complicated electrochentical system such as that of composite electrodes [34]. 

Applying all three techniques to time drifting systems, quasi-steady-state impedance spectra at defined times can be obtained, namely time resolved electrochemical impedance spectra (TREIS). In Figure 4.5.44, for illustration, an EIS recorded at the PEFC with flooded cathode, after 4450 s of dead end operation at 2 A, is given (for details see 4.5.4.3). 

Electrochemical impedance spectroscopy (EIS) is an established method for the investigation of a wide range of electrochemical systems (Barsoukov and Macdonald 2005). A prerequisite for many evaluation methods is the analysis of the similarity of two impedance spectra for example when assessing the quality of fit or when describing the magnitude of state changes. This requires a scalar measure for the distance between two impedance spectra. 

In an laboratory environment, state determination of Li-ion cells is often accomplished with Electrochemical Impedance Spectroscopy (EIS). Using these impedance spectra, impedance-based models are parameterized in the frequency domain with well-known fitting procedures. These models are designed to reduce the dimension of the measurement data in order to describe the state of a Li-ion cell with few parameters. The parameters of these models can than be used to determine the cell s current state (SOx). There exists a variety of impedance-based models represented by electrical equivalent circuits. 

Extensive efforts have been directed toward the search for oxide materials that allow fabrication of an SOFC with low activation and ohmic losses. To determine the role of new materiak in the overall fuel cell performance, electrochemical impedance spectroscopy (EIS) has been used to measure the activation and/ or ohmic resktance contributed by the specific new material. An impedance spectrum k obtained by applying a periodic change in voltage and monitoring the current response at varying frequencies. The impedance spectra obtained... 

Features of the impedance spectra of Fig. 3.15a may be modeled by a simple modified Randles-Ershler equivalent circuit shown in Fig. 3.15c. In this model, is the solution resistance, and is the charge-transfer resistance at the electrode/eIectrol e interface. A constant phase element (CPE) was used instead of a doublelayer capacitance to take into account the surface roughness of the particle. Qn is the insertion capacitance, and Zw is the Warbui impedance that corresponds to the solid-state diffusion of the Li-ion into the bulk anode. The Warburg element was used only for impedance data obtained at the tenth charge. The electrical components of the surface film which is likely formed on the electrode were disregarded, because no time constant related to this process could be seen in the electrochemical impedance spectroscopy (EIS) spectra. It was also checked that their inclusion in the model of Fig. 3.15c does not improve the fit. 

This chapter has provided background on electrochemical interfaces and the relationships between impedance spectra and electrochemical interface, for fuel cell researchers or engineers who may not be electrochemists but will apply EIS as... 

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