Figure shows the calculated reaction free energy of the OER process at U=0 V for the Na-doped Li 2 O 2 surface (blue line) in comparison with the corresponding for the pristine Li 2 O 2 (red line). We can see that the energy cost of taking out the Li in the first step is considerable smaller in the Na-doped surface. The reason for this is that the doped case presents an initial level of distortion that makes this surface less bound. Similar arguments are valid for the following steps of the OER process. The main results of this study is that the more limiting step of the OER, that is, the last LiO 2 removal, presents a sensible reduction (266 meV for the simulated supercell) for the doped case as compared to the pristine surface.