For O-GEIS measurements, the impedance spectrum starts to become visibly distorted once the NSD reaches ~ 10%, which occurs below a frequency of ~ 10 Hz (Fig. ). A conservative limit of 3% NSD was set, which limits the lower frequency to 100 Hz at 25 mA cm -2 applied current density. A frequency range of 100 -794 Hz is still sufficient to fit half of the semicircle with equivalent-circuit analysis, and most of the data for each spectrum maintains NSD of < 2% (Fig. ). Overall, although non-stationarity restricts the lower frequency limit of O-GEIS measurements, satisfactory data to measure the interfacial kinetics can still be obtained at relatively high current densities.