Electrochemical impedance spectroscopy charge transfer process

The above formulas may become inapplicable for systems with adsorption processes or/and coupled chemical steps in solution whose characteristic times are comparable with the inverse frequency within the impedance measurement interval. In this case the charge-transfer resistance, Rct, must be replaced by a complex charge-transfer impedance, Zct. Another restriction of this treatment is its assumption of the uniform polarization of the m s interface which requires to ensure a highly symmetrical configuration of the system. Refs. [i] Sluyters-Rehbach M, Sluyters JH (1970) Sine wave methods in the study of electrode processes. In Bard A/ (ed) Electroanalytical chemistry, vol. 4. Marcel Dekker, New York, p 1 [ii] Bard A], Faulkner LR (2001) Electrochemical methods, 2nd edn. Wiley, New York [iii] Retter U, Lohse H (2005) Electrochemical impedance spectroscopy. In Scholz F (ed) Electroanalytical methods. Springer, Berlin, pp 149-166 [iv] Bar-soukov E, Macdonald JR (ed) (2005) Impedance spectroscopy. Wiley, Hoboken... 

The interfacial reactivity of functional electrodes can mostly influence the amperometric detection signal in the bioelectrocatalytic process. Herein, the electrochemical impedance spectroscopy (EIS) has been applied to investigate the interfacial charge transfer or mass transfer process of bare Ti02/Ti substrates and G0D-Ti02/Ti composite electrodes. The EIS measurements over a frequency from 100000 to 0.01 Hz are carried out in a conventional three-electrode system under a sinusoidal perturbation of 5 mV and a constant potential of -0.4 V. 

IMPS uses modulation of the light intensity to produce an ac photocurrent that is analysed to obtain kinetic information. An alternative approach is to modulate the electrode potential while keeping the illumination intensity constant. This method has been referred to as photoelectrochemical impedance spectroscopy (PEIS), and it has been widely used to study photoelectrochemical reactions at semiconductors [30-35]. In most cases, the impedance response has been fitted using equivalent circuits since this is the usual approach used in electrochemical impedance spectroscopy. The relationship between PEIS and IMPS has been discussed by a number of authors [35, 60, 64]. Vanmaekelbergh et al. [64] have calculated both the IMPS transfer function and the photoelectrochemical impedance from first principles and shown that these methods give the same information about the mechanism and kinetics of recombination. Recombination at CdS and ZnO electrodes has been studied by both methods [62, 77]. Ponomarev and Peter [35] have shown how the equivalent circuit components used to fit impedance data are related to the physical properties of the electrode (e.g. the space charge capacitance) and to the rate constants for photoelectrochemical processes. 

Electrochemical Impedance Spectroscopy. Electrochemical Impedance Spectroscopy (EIS), a non-destructive investigative technique enables an insight into the corrosion process not obtained by DC techniques. EIS provides information on reaction parameters, corrosion rates, oxide characteristics and coating integrity, data on electrode interfacial capacitance and charge transfer resistance. It provides... 

Two types of impedances are measured in electrochemical impedance spectroscopy (EIS) faradic and nonfaradic. Faradic impedance is associated with the process which involves transfer of charge across an interface. In faradic impedance measurement, a redox probe is used which is alternately oxidized and reduced due to transfer of electrons to and from the metal electrode resulting from the biological events occurring near the electrode surface. Nonfaradic impedance (mostly capacitive measurements) on the other hand is associated with transient flow of current or displacement current without actual transfer of any electron. In this case, no redox probes are required. 

Electrochemical Impedance Spectroscopy (EIS) as schematically shown in Eigure 3.10 requires an alternating current (AC) and the output is a Nyquist plot for charge-transfer or diffusion control process, which can be used to determine Rv, which in turn, is inversely proportional to the corrosion current density icorr-... 

As to purely electrochemical techniques, also simple voltammetric techniques in the presence of reversible redox couples in solution can give a clear indication of the actual deposition of the nanostructure on the electrode surface and of the effects on the charge transfer resistance. This information can be complemented by impedance spectroscopy (EIS) investigations, which evidence changes in charge transfer process at the electrode/solution interface before and after electrode modification. 

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. 

The above mentioned sections deal with bulk phenomena. The other important area about which impedance spectroscopy gives important information is that of the electrochemical interface. This is usually a junction between an electronic and an ionic conductor electrochemical devices utilize the charge transfer that occurs at this interface. The kinetics of this process as well as the electrical nature of the interface region are discussed in Section 2.1.4. 

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