Other Pore Geometry with Ohmic Drop in Solution Only

2 Other Pore Geometry with Ohmic Drop in Solution Only 

The cylindrical pore model is an idealization of a real porous electrode. Other pore geometries were also studied. De Levie [413] obtained an analytical solution for the impedance of V-grooved pores. Such pores might be obtained, for example, by scratching the electrode surface. A cross section of such a groove is displayed in Fig. 9.8. Its impedance per unit of groove length is 

I is the groove depth (normal to the surface), and Z ei is the double-layer impedance per unit of the true surface area. Equation (9.14) reduces to the impedance of a perfectly flat surface for ji = 90° and to the impedance of cylindrical porous electrode for p = 0°. Gunning [414] obtained an exact solution of the de Levie grooved surface not restricted to a pseudo-one-dimensional problem in the form of an infinite series. Comparison with de Levie s equation (9.14) shows that the deviations arise at higher frequencies or, more precisely, at high values of the dimensionless parameter Q. = coC ialp, where a is half of the distance of the groove opening, a = Itan p (Fig. 9.8). 

The pear-shaped pores predict the formation of a semicircle on the complex plane plots that might be confused with a semicircle related to the coupling of the charge transfer resistance and double-layer capacitance. Such effects were observed experimentally for hydrogen evolution on porous electrodes [415, 416, 419, 420]. This suggests that at some electrodes, pores of a pearlike shape are present 

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