Localized electrochemical impedance measurements

The advent of ever smaller electrochemically cells (microcells, capillary cells) which can be placed on selected areas of an electrode surface allows spatially resolved measurements of local properties. Spectroscopic methods modified in such a way like e.g. locally resolved electrochemical mass spectrometry have been treated in previous sections. Optical methods incorporating scanning probes wiU be treated below. Classical electrochemical methods like e.g. impedance measurements employing these miniaturized cells [1] thus providing localized information will not be treated in this book. The same applies to scanning electrodes employed in localized electrochemical impedance measurements (LEIS). 

E. Bayet, F. Hnet, M. Keddam, K. Ogle, and H. Takenonti, Adaptation of the scanning vibrating electrode techniqne to ae mode local electrochemical impedance measurement, Mater. Sci. Forum 289-292 51 (1998). 

F. Zou and D. Thierry, Diffusion effects in localized electrochemical impedance measurements by probe methods, /. Electrochem. Soc. 146 2940 (1999). 

Measixrement techniques Bridge mechanical generator Bridge electronic generator Impulse method, oscillograph, Laplace transform Analogue impedance measurement, potentiostat (AC + DC) Digital impedance measurement, cormection with computer Local electrochemical impedance spectroscopy (LEIS)... 

F. Zou, D. Thierry, and H. S. Isaacs, "High-Resolution Probe for Localized Electrochemical Impedance Spectroscopy Measurements," Journal of The Electrochemical Society, 144 (1997) 1957-1965. 

Lillard and coworkers developed a method called Local Electrochemical Impedance Spectroscopy LEIS [39). It relies on the fact that ac current densities in the solution very near to the working electrode are proportional to the local impedance properties of the electrode. In order to determine the current densities normal to the surface, the ac potential drop was measured between planes parallel to the electrode surface employing a two-electrode microprobe. A schematic of a commercially available experimental setup for LEIS is... 

Nickel-base alloys respond well to most electrochemical test techniques and show active-passive behavior in many environments. Due to their rapid repassivation, however, the results obtained with potentiod3mamic techniques can sometimes be affected by scan rate and immersion time prior to starting the test [5,6], Electrochemical techniques are useful for investigating localized corrosion resistance, ASTM G 61, Test Method for Conducting Cyclic Potentio-dynamic Polarization Measurements for Localized Corrosion Susceptibility of Iron-, Nickel-, or Cobalt-Based Alloys, and general corrosion resistance, ASTM G 59, Practice for Conducting Potentiodynamic Polarization Resistance Measurements of nickel alloys. Electrochemical impedance measurement techniques have not been extensively applied to nickel alloys. 

Microcapillaiy electrochemical cells are widely used in biology for local potential measurements at a very reduced size. In corrosion, pioneering work was performed for promoting the Scanning Reference Electrode Technique (SRET) in this case the microcapil-laiy is immersed in the bulk electrolyte and local potential or local electrochemical polarization or local electrochemical impedance has been measnred. 

Takenouti, H., G. Galicia, M. Keddam, and V. Vivier, Vibrating single probe and stationary bi-probes to measure local electrochemical impedance spectroscopy, Bulgarian Chemical Communications, 38, 2006, 165. 

Brett DJL, Atkins S, Brandon NP, Vesovic V, Vasileiadis N, Kucemak A (2003) Localized impedance measurements along a single channel of a solid polymer fuel cell. Electrochem Solid-State Lett 6 A63-6... 

The methods described in this chapter and this book apply to electrochemical impedance spectroscopy. Impedance spectroscopy should be viewed as being a specialized case of a transfer-function analysis. The principles apply to a wide variety of frequency-domain measurements, including non-electrochemical measurements. The application to generalized transfer-function methods is described briefly with an introduction to other sections of the text where these methods are described in greater detail. Local impedance spectroscopy, a relatively new and powerful electrochemical approach, is described in detail. 

A number of methods exist for the study of surface diffusion ex-situ [11-13]. The STM noise method, discussed above, has its own advantages (or shortcomings) as the local probe method. However, for the electrochemical interface it seems to be unique. (The impedance measurements [14] may not always be unambiguously interpreted, and nor do they give the local information about the surface.) We thus expect that the STM noise method will be widely used for in-situ study of surface diffusion, as long as the resolution of the high frequency noise measurements improves. Then the maps of local adatom difflisivity on metal electrodes will become a reality. 

Atomic force microscopy (AFM) and electrochemical atomic force microscopy (ECAFM) have proven usefiil for the study of nucleation and growth of electrodeposited CP films on A1 alloy [59]. AFM was used to study adhesion between polypyrrole and mild steel [60], whereas electric force microscopy (EFM) has been used to study local variations in the surface potential (work function) of CP films [61]. AFM with a conductive tip permits a nanoscale AC impedance measurement of polymer and electrolyte interfaces, permitting differentiation between highly conductive amorphous regions and less-conductive crystalline regions of the CP film [62]. 

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