Physical interpretation of the Warburg impedance

Journal Article · Fri Sep 01 04:00:00 EDT 1995 · Corrosion

DOI:https://doi.org/10.5006/1.3293628· OSTI ID:116513

Taylor, S R ^[1]; Gileadi, E ^[2]

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1. Univ. of Virginia, Charlottesville, VA (United States). Center for Electrochemical Science and Engineering
2. Tel-Aviv Univ., Ramat-Aviv (Israel). School of Chemistry

Electrochemical impedance spectroscopy (EIS) has become a very important tool in the analysis of corrosion and essentially all electrochemical phenomena. In the evaluation of impedance data, the electrochemical interphase often is described by an equivalent circuit relevant for the conditions of the experiment, using circuit elements that represent the various physical processes present. However, this approach is limited in that the use of passive elements, such as capacitor or a physical distribution of capacitors (e.g., in a transmission line), to describe other phenomena such as adsorption and mass transport (via the Warburg impedance [Z{sub W}]), mathematically may mimic the voltage-current characteristics of the process to be modeled but does not provide an understanding of the phenomena taking place. The physical origin of the capacitive behavior of (Z{sub W}) and adsorption pseudocapacitance is discussed. A simple derivation of Z{sub W}, based only on the Nernst diffusion layer thickness ({delta} = ({pi}Dt){sup 1/2}), is presented. An alternate equivalent circuit is proposed in which Z{sub W} is represented by a series combination of a resistor (the Warburg pseudoresistance [R{sub W}]) and a capacitor (the Warburg pseudocapacitance [C{sub W}]). The values of these new circuit elements are independent of potential. On the other hand, they are proportional to {omega}{sup {minus}1/2}, leading to the so-called constant phase element that is observed experimentally. In contrast, the usual elements employed in equivalent circuit models to describe the voltage-current characteristics of the interphase (e.g., the faradaic resistance, double-layer capacitance, and adsorption pseudocapacitance) are independent of frequency but may change with potential over many orders of magnitude. It is shown that the frequency dependence of C{sub W} and R{sub W} follows from the well-known dependence of {delta} on the square root of time.

• Sponsoring Organization: USDOE
• OSTI ID: 116513
• Journal Information: Corrosion, Journal Name: Corrosion Journal Issue: 9 Vol. 51; ISSN 0010-9312; ISSN CORRAK
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
CAPACITANCE
DATA ANALYSIS
ELECTRIC IMPEDANCE
ELECTRIC POTENTIAL
ELECTROCHEMICAL CORROSION
ELECTRONIC CIRCUITS
MATHEMATICAL MODELS
SIMULATION
SPECTROSCOPY