In this study, we draw a direct comparison to the weak-binding Au(111) surface and investigate O 2 adsorption as the first step of the ORR on Pt(111). While we do not expect this step to be rate-determining here, the response to potential and even the mode of O 2 binding under ORR conditions have so far remained unclear. In contrast to Au(111), we find negligible potential dependence in the binding of (molecular) O 2 at Pt(111); a result which persists for both the clean surface and a more realistic OH-covered catalyst model. By decoupling the O 2 potential response into contributions of different physical origin, we explain the contrast to Au(111) through the inherently different reactivity of the two metal surfaces.