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 Rp=2.550t0.69/Ctotal−2.986Re where t0.69 is the time of 69% response on the charge–time curve. The total double layer capacitance (Ctotal) can be obtained from the equation Ctotal=Q/η0, where Q is the plateau charge on the chronocoulometric curve and η0 is the amplitude of the potential step. Re is the uncompensated solution resistance between the Luggin tip and the front surface of the porous electrode, and Re=η0/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.