we have evaluated jk in the entire potential range studied here (Figure , c) and found it reaches up to 30±2 mA cm -2 (geometric) at 0.35 V vs. RHE. Error is associated with uncertainties due to the noise in limiting currents under diffusion conditions. Further, we have performed Tafel analysis on such reconstructed mass transfer-corrected kinetic currents and found that in the anodic scan, there is a continuous change of Tafel slope from low to high values. However, in the cathodic scan, the regions of different Tafel slopes were better separated, revealing the low Tafel slope region (-(67±2) mV dec -1 , from 0.85 to 0.81 V vs. RHE), medium Tafel slope (-(105±3) mV dec -1 , from 0.80 to 0.75 V vs. RHE), and high Tafel slope (-(217±2) mV dec -1 , down to 0.52 V vs. RHE). This behavior is similar to that of Pt revealed by using single submicrometer Pt particles , showing three ranges with different ORR Tafel slopes (-60, -105, and -240 mV dec -1 ). Such behavior has been explained by the potential-dependent change in the oxide coverage and possible change of the ORR rate-determining step at high ORR overvoltages .