Diffusion electrochemical impedance spectroscopy

When the characteristic time for charge diffusion is lower than the experiment timescale, not all the redox sites in the film can be oxidized/reduced. From experiments performed under these conditions, an apparent diffusion coefficient for charge propagation, 13app> can be obtained. In early work choroamperometry and chronocoulometry were used to measure D pp for both electrostatically [131,225] and covalently bound ]132,133] redox couples. Laviron showed that similar information can be obtained from cyclic voltammetry experiments by recording the peak potential and current as a function of the potential scan rate [134, 135]. Electrochemical impedance spectroscopy (EIS) has also been employed to probe charge transport in polymer and polyelectrolyte-modified electrodes [71, 73,131,136-138]. The methods... 

However, as mentioned previously, gas-diffusion electrodes usually deviate substantially from traditional electrochemical—kinetic behavior, often being limited by multiple rate-determining factors and/or changes in those factors with overpotential or other conditions. In attempting to analyze this type of electrode, one of the most influential experimental techniques to take hold in the solid-state electrochemical literature in the last 35 years is electrochemical impedance spectroscopy (EIS)—also know as a.c. impedance. As illustrated in Figure 6, by measuring the sinusoidal i— response as a function... 

Electrodeposition on transparent material such as indium tin oxide (ITO) can be used for electrochromic applications [328]. Pb deposition on indium-tin oxide electrode occurs by three-dimensional nucle-ation with a diffusion-controlled growth step for instantaneous nucleation [329], and the electrode process has also been studied using electrochemical impedance spectroscopy [328]. 

Finite diffusion — Finite (sometimes also called -> limited) diffusion situation arises when the -> diffusion layer, which otherwise might be expanded infinitely at long-term electrolysis, is restricted to a given distance, e.g., in the case of extensive stirring (- rotating disc electrode). It is the case at a thin film, in a thin layer cell, and a thin cell sandwiched with an anode and a cathode. Finite diffusion causes a decrease of the current to zero at long times in the - Cottrell plot (-> Cottrell equation, and - chronoamperometry) or for voltammetric waves (see also - electrochemical impedance spectroscopy). Finite diffusion generally occurs at -> hydrodynamic electrodes. 

The immittance analysis can be performed using different kinds of plots, including complex plane plots of X vs. R for impedance and B vs. G for admittance. These plots can also be denoted as Z" vs. Z and Y" vs. Y, or Im(Z) vs. Rc(Z), and Im( Y) vs. Re( Y). Another type of general analysis of immittance is based on network analysis utilizing logarithmic Bode plots of impedance or admittance modulus vs. frequency (e.g., log Y vs. logo)) and phase shift vs. frequency ( vs. log co). Other dependencies taking into account specific equivalent circuit behavior, for instance, due to diffusion of reactants in solution, film formation, or electrode porosity are considered in - electrochemical impedance spectroscopy. Refs. [i] Macdonald JR (1987) Impedance spectroscopy. Wiley, New York [ii] Jurczakowski R, Hitz C, Lasia A (2004) J Electroanal Chem 572 355... 

Finite-space diffusion takes place during the charging of insertion electrodes at moderate frequencies, transforming into mainly capacitive behavior within the limit of very low frequencies, in contrast to the semi-infinite diffusion for solution redox-species (except for thin-layer solution electrochemistry) electrochemical impedance spectroscopy becomes a very useful diagnostic tool for the characterization of insertion mechanisms ... 

Although simple impedance measurement can tell the existence of an anodic film, electrochemical impedance spectroscopy (EIS) can obtain more information about the electrochemical processes. In general, the anode/electrolyte interface consists of an anodic film (under mass transport limited conditions) and a diffuse mobile layer (anion concentrated), as illustrated in Fig. 10.13a. The anodic film can be a salt film or a cation (e.g., Cu ) concentrated layer. The two layers double layer) behave like a capacitor under AC electric field. The diffuse mobile layer can move toward or away from anode depending on the characteristics of the anode potential. The electrical behavior of the anode/electrolyte interface structure can be characterized by an equivalent circuit as shown in Fig. 10.13. Impedance of the circuit may be expressed as... 

Cadmium atomic layer electrodeposition above reversible Cd2+/Cd potential (underpotential deposition, upd) on bulk tellurium and Te atomic layer predeposited on gold has been characterised with potentiodynamic electrochemical impedance spectroscopy (PDEIS) by variations, with the electrode potential E, of double layer pseudocapacitance Q,u, charge transfer resistance Rrt and Warburg coefficient Aw of diffusion impedance. 

Electrochemical Impedance Spectroscopy (ElS) is a method used to characterize electron-transfer reactions by perturbing the system in a sinusoidal manner over a wide range of frequencies. This method, which is very sensitive to the properties of the electrode interface, provides information regarding electron-transfer kinetics, diffusion of charged species, charging/discharging, and system conductance. 

Figure 43 2. Diffusion coefficients far LA in crystalline (a) and disordered (i>) WO3 as obtained from electrochemical transient current measurements and from electrochemical impedance spectroscopy (Strpmme Mattsson [2000]). The diffusion coefficient obtained by impedance spectroscopy is the chemical diffusion coefficient relevant for a specific composition (specified on the upper x axis), while that obtained from the current measurements is an average diffusion coefficient for all compositions lower than the composition value specified on the upper x axis.

Insight into the electroreduction of nitrate ions at a copper electrode, in neutral solution, after determination of their diffusion coefficient by electrochemical impedance spectroscopy. Electrochim Acta 55 7341-7345... 

As discussed in piAL 11], using electrochemical impedance spectroscopy (EIS) to analyze a PEM electrolyzer very clearly reveals slow diffusion dynamics (very low frequencies), and less clearly, fast diffusion dynamics (low/medium frequencies) and very fast diffusion dynamics (high/very high frequencies). As, for our purposes, the truth of this observation is veiy comprehensive, we shall consider it to be general hereafter. 

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