Our focus turns in the following to the kinetic competition between the four elementary steps directly after OOH*. Among these steps, the two PCETs are distinguished from one another by whether the H + attacks the inner (path (iii)) or outer (path (i)) O adsorbate atom. The surface-bound aquoxyl (OOH 2 *) species formed in the latter case is predicted to be metastable within vacuum-background DFT models, though energetically quite unfavorable (1.1 eV higher in energy as compared to HOOH*). The aquoxyl O-O bond is specifically weak and prone to spontaneously breaking during our dynamical simulations of the electrochemical H 2 O/Au(111) interface. As a result, we cannot decouple protonation within the aquoxyl path (i) from direct OOH* dissociation within the dissociative path (ii) using a single (intuitive) reaction coordinate. We therefore resort to two-dimensional umbrella sampling, while adopting the following CVs: the O-H coordination number ξ -which is well suited for describing OOH 2 formation (x-axes in Fig. ) and the O-O interatomic distance to describe dissociation (y-axes in Fig. ). The results are shown in Fig. with the underlying free energy landscape as a color heatmap such that the more stable regions are represented by yellow and the less stable regions by darker red, while always setting the lowest-energy configuration (usually the initial OOH*, except for Fig. 12 these conditions to ca. 0.7 eV. The origin of this decrease likely lies in increasingly favorable dipole-field interactions within the O OH* transition state 42 and implies accelerated rates on the order of 10 0 -10 3 s -1 . The predicted barriers from this analysis are also similar to the average values extracted over four independent simulation runs within one-dimensional umbrella sampling (SI, Table ). We overall conclude from Fig. therefore that the kinetic competition between the two elementary steps (i)-(ii) is won by direct OOH* dissociation, namely a non-PCET "chemical" step. This result is regardless of the high thermodynamic stability of the final PCET state.