Determination of the ionic resistance in a porous electrode using chronocoulometry

Abstract

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=2.550 t 0.69/ C total−2.986 R 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/ η 0, where Q is the plateau charge on the chronocoulometric curve and η 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= η 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 1 and 6 mol l −1 KOH solutions.