Current distribution at a disk electrode during a current pulse

The spatio-temporal evolution of the current distribution at a disk electrode during a current pulse has been examined within the mathematical formalism introduced by Nişancioǧlu and Newman[J. Electrochem. Soc., 120, 1339 (1973)]. Under conditions in which the disk electrode-electrolyte interface can be represented by a capacitor (double layer) in parallel with a resistor (linearized faradaic process), the dominant contribution to the total disk current density, iT, immediately following application of the current step, is capacitive, iC. During this period, both iC and the significantly smaller faradaic component of iT, iF, are highly nonuniform over the disk surface, attaining maximum values at its edge. At longer times, iC decreases and iF increases, becoming the only contribution to iT when steady state is reached. Upon current interruption, the charged interface relaxes via two distinct pathways: a faradaic shorting of the double layer and a redistribution of the charge stored in the interfacial capacitor, which, for the electrolyte plate, generates current loops extending far into the solution that terminate near the edge of the disk electrode. This zero total current condition across the entire electrode leads to the development of a concentric ring, where iC and iF are equal in magnitude but opposite in sign, which propagates toward the center of the disk as steady state is approached.