High-frequency resistance (HFR) values are extracted from the electrochemical impedance measurements at each current density by fitting a frequency interval of 50 -0.5 kHz with an equivalent circuit model comprising an inductance, a resistor, and a transmission line model in series. Fitting was performed using an in-house developed Python routine based on NumPy 38 , SciPy 39 , pandas , matplotlib and impedance.py . An exemplary Nyquist plot with fit can be found in Fig. . HFR-free polarization curves are derived by subtracting the product of HFR and current density from the polarization curve. A Tafel analysis is not conducted in the full cell measurements since, for the tests with low loadings, the Tafel requirements are not fulfilled in the lowest current density region and a measurement to even lower current densities is not feasible due to resolution limitations.