Determination of the ionic resistance in a porous electrode using chronocoulometry

The purpose of the work is to establish a simplified method, which is easy to use and yet sufficiently accurate for the determination of ionic resistance in porous electrodes. The equation of the chronocoulometric transient following a potential step is deduced for porous electrodes in the double layer region based on a one-dimensional transmission line model. According to the result of numerical calculations, the internal ionic resistance is R-p = 2.550t(0.69)/C-total - 2.986R(e) where t(0.69) is the time of 69% response on the charge-time curve. The total double layer capacitance (C-total) can be obtained from the equation C-total = Q/eta(0), where Q is the plateau charge on the chronocoulometric curve and eta(0) is the amplitude of the potential step. R-e is the uncompensated solution resistance between the Luggin tip and the front surface of the porous electrode, and R-e = eta(0)/I(0) where I(0) is the current at the beginning of the potential step. The theoretical error of the approximate equation is below 0.7%. The validity of the proposed method is well supported by the experimental data obtained for a porous silver electrode in I and 6 mol l(-1) KOH solutions. (C) 2002 Elsevier Science B.V. All rights reserved.