Fleig proposed that the buffering effect was due to limited coverage of adsorbed gas on the surface at the PZC. On the mechanism for charge transfer, the ambipolar charge transfer reaction has been decoupled by slow IT. This agrees with the derivation in Table , where the IT step yields the experimentally given relationship ∆χ ≈ -η act . While we strongly believe that the results of this study show that O 2 reduction on MIEC surfaces is driven by χ, we must also note that the exact mechanism is subject to discord. Therefore, we do not intend to further speculate on the mechanistic details in this study.