The effect of pore size distribution on the frequency dispersion of porous electrodes

The transmission line model with pore size distribution (TLM-PSD) developed for blocking electrodes without faradaic reactions in our previous work was reformulated on the basis of the distribution of the penetrability coefficient alpha(0), which is a more generalized concept than the distribution of pore size. Impedances were simulated using the TLM-PSD model for four different pore size distributions (PSD). Although different shapes of the Nyquist curve was obtained depending upon the different PSD, all simulated impedances share a common point that an increase in the width of a distribution (P-sigma) leads to a more inclined Nyquist curve at high penetrability (alpha(mu)). This is because the effect of small pores on the total impedance increases with P-sigma. We fitted the experimental impedance data of a carbon membrane with the TLM-PSDs and the de Levie's model (TLM-delta). The fitting by TLM-PSD was successful while TLM-delta could not describe the impedance of the porous electrode at low frequency range. In addition, the geometric parameters estimated by TLM-PSD agreed with physically available values. (C) 2000 Elsevier Science Ltd. All rights reserved.