We efficiently sample the free energy along a particular CV by adopting the following procedure: We first equilibrate the initial state through AIMD (5 ps equilibration time) and then run a short metadynamics simulation until the relevant CV range is visited at least once. This allows to place windows for umbrella sampling at regular intervals along the given CV. Using initial conditions from the metadynamics, each window is sampled for 5 ps. All simulations sample the NVT ensemble at 300 K using a Nosé-Hoover thermostat with a 40 fs damping coefficient and 1 fs timestep. Four independent simulations with different starting H 2 O structures are performed to generate each of the one-dimensional free energy curves in Fig. . The results show that the error from sampling different metastable H 2 O configurations 37 on the predicted activation energies is generally small (<0.1 eV) for this particular system (cf. values in SI, Table ). We therefore neglect this effect in the computationally much more demanding two-dimensional sampling that underlies Figures and. Our protocol for umbrella sampling in one and two dimensions as well as the corresponding analyses of output data are described in full detail in Sections S4. where its chemical potential is determined by the electrolyte pH. As a result, our "pseudofinal" simulated end states can be considerably higher in energy (less stable) compared to those of the full thermodynamic process and this inconsistency is to be kept in mind when considering the reported reaction energies. On the other hand, as the primary focus of this study, activation energies should be accurately captured as the free energy difference between the initial and transition states while assuming that the latter occurs with the donating H 2 O still in the near-surface region (further discussion included in the SI, Section S5).