O-GEIS measurements were conducted between the frequency range of 100 -794 Hz, with an applied current density ranging from 5 to 25 mA cm -2 , and a current excitation of 10% of the applied current (0.5 -2.5 mA cm -2 ). The maximum current and minimum frequency were limited to ensure stationarity, and NSD of < 3% was maintained for all measurements. The data were collected with a single impedance point per scan with no averaging, and with the EC-Lab drift correction feature enabled. Between each scan, the cell was held at 0 V applied voltage for rest times ranging from 2 min at 5 mA cm -2 to 5 min at 25 mA cm -2 . PEIS spectra were collected between each current density to ensure stability. Before and after collecting the O-GEIS dataset, which took ~ 3 h, the impedance measured with PEIS increased by 0.6% (Figure ). The raw impedance data for the entire dataset is shown in Fig. . The differential charge-transfer resistance (𝑅 𝑐𝑡 ′ ) at each applied current is quantified by fitting each impedance spectrum to an equivalent-circuit model of Z = RΩ + Rct/Q, with the value of RΩ measured with PEIS (Fig. ).