Electrochemical impedance of partially and totally blocked electrodes

E M ANDRADE; F. V. MOLINA

Encyclopedia of Surface and Colloid Science

Taylor and Francis

Lugar: New York; Año: 2006; p. 2048 - 2064

The electrochemical impedance measurement is a technique that has been used for long time to study electrochemical processes at electrode surfaces. In electrochemical impedance experiments, a small AC voltage perturbation is applied to an electrode/solution interface, the resulting alternate current intensity is measured and a corresponding electrical impedance, the electrochemical impedance, is obtained. In some techniques such as AC voltammetry and AC polarography the AC intensity at a fixed frequency is studied as a function of the DC applied potential. In electrochemical impedance spectroscopy (EIS) the impedance is measured as a function of the AC frequency (at one or several DC potential values) and an equivalent circuit (EC), is deduced from the measurements. The EC is an electrical circuit composed of resistors, capacitors, inductors and other special components such as constant phase elements (CPE), which serve as an electrical model of the physical interface. The components of the EC are then related to physical features and/or processes at the electrode/solution interface through suitable modeling. Thus, EIS gives in a relatively straightforward way an electrical characterization of the electrochemical system, but establishing the relationship between this characterization and the physical system behavior is more difficult. Nevertheless, EIS has been (and is) applied, among other topics, to the study of faradaic electrode reactions, characterization of rough and porous electrodes, and partially or totally blocked electrodes. This field includes problems such as adhesion of particles and scale deposits, passivation and corrosion of metals, and performance of protective coatings. These last two topics are the most important practical applications of EIS, allowing the investigation of protection methods such as corrosion inhibitors, conversion and barrier coatings, oxide layers and cathodic protection. The adhesion performance and water uptake of protective coatings can also be tested using EIS, which is nearly the only non destructive technique available to study those problems. In this chapter, we will present shortly the basics of EIS, discuss measurement techniques, and review examples of recent applications to blocked electrodes.