More complex systems, porous electrodes, and fractals

10 More complex systems, porous electrodes, and fractals 

Many electrode processes are more complex than those discussed above. Besides this, the impedance of an interface is dependent on its microscopic structure which, in the case of a solid electrode, can have an important influence. Impedance measurements can be used to study complicated corrosion phenomena (Chapter 16), blocked interfaces (i.e. where there is no redox process nor adsorption/desorption), the liquid/liquid interface2425, transport through membranes26, the electrode/solid electrolyte interface etc. Experimental measurements always furnish values of Z and Z or their equivalents Y and Y , or of the complex permittivities e and e (e = Y/icoCc, Cc being the capacitance of the empty cell). In this section we attempt to show how to 

Two types of electrical analogy model for the interpretation of impedance data can be used based on combinations of resistances and capacitances, or based on transmission lines. These possibilities are now described. 

Transmission lines have been much used recently to simulate interfaces, especially where the solid is rough. We consider, to illustrate, a simple transmission line (Fig. 11.17). 

Termination in an open circuit (corresponding to reflection) as in conducting polymers and porous electrodes, such as porous carbon in acid media (Fig. 11.186). 

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