





RESOURCES > EIS > POROUS ELECTRODES > de LEVIE Interest in fuel cells and supercapacitors has lead to renewed attention to porous electrodes.
The de Levie ModelOne of the first treatments of a porous electrode was by de Levie in the late 60's (Ref 1). He assumed cylindrical pores in a metallic electrode. The solution in the pores is assumed to be homogeneous so that its conductivity does not depend on the distance down the pore. The figure to the left shows a schematic for a transmission line model of the de Levie impedance. The electrolyte resistance through the pore is Ro ohm/cm and the interfacial impedance is Z_{IF} ohmcm^{2}. For a small length of the pore, dx, the electrolyte resistance, dR, and interfacial impedance, dZ are given by the equations, below. The radius of the pore is r cm, and the resistivity of the electrolyte is ohmcm. Zo is the impedance at the pore wallelectrolyte interface for a unit length of pore. de Levie showed that the impedance of a single pore of length l had an impedance given by Z_{PORE}. This equation holds for any type of interfacial impedance as long as the interfacial impedance does not depend upon the position in the pore.
If all of the n pores in an electrode are identical (radius r and length l) the equation for Z_{PORE} can be used to obtain the total experimental electrode impedance if the interfacial impedance ( Z_{IF} ) is known (Ref 2). Barcia, et. al.( Ref 2 ) applied this equation to the cast iron corrosion in water and copper dissolution in HCl. In both cases, fairly complicated models were used for Z_{IF}. They also point out that, although the pores are not all of uniform radius and depth, average radii and depth can be extracted from the EIS data.


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