, the E1/2 for oxygen reduction will correspond to the voltage of this first redox reaction, which is consistent with the proposed outer-sphere electron transfer for the initial reduction of O2. Here, we take the E1/2 for oxygen reduction to correspond to the largest increase in reduction current (~0.17 V vs. RHE), though we note the initial activity in p(gPyDPP-MeOT2) is likely caused by exposure of the underlying glassy carbon substrate. In agreement with this finding regarding the crucial nature of the first electrochemical step, p(g3T2), a p-type OMIEC, does not effectively reduce oxygen through the EC'D mechanism with high activity because of the lack of ion-insertion redox at appropriate reduction voltages (Figure )-although here too there is likely some exposure of the underlying glassy carbon substrate.