Fig. 5: The interface effect of MEA.

a, b The secondary ion two-dimensional imaging from ToF-SIMS, a Fe–NC, b Fe–NC^BrCl. The green is S⁻, the red is Fe⁺. c Integral SO₃⁻ distribution in cathode catalyst layer shows intensity gradients from both Fe–NC (blue) and Fe–NC^BrCl (red) catalysts. d Relationship between R_total and absolute gas pressure obtained by the limiting current method. Insets were R_np and R_p. e An Arrhenius plot of i₀ obtained from the Nyquist plots shown in Supplementary Fig. 37. f Nyquist plots for PEMFCs of indicated cathode catalysts at the current density of 1.0 A cm^–2, the inset shows the equivalent circuit model, R_ct and R_mt of Fe–NC and Fe–NC^BrCl obtained by EIS fitting. Error bars represent the standard deviation of the fitting results.