The OER activity volcano including active sites from this system is presented in fig. . Note that the benchmark catalyst IrO 2 has been marked as a pointer for what should be considered highly active. Together with the IrO 2 on the strong binding side of the volcano lies the AC4 (Ni in positions A and C, active site at position 4) point following the ruthenium pathway. This point serves to illustrate the high catalytic activity of the ruthenium CUS sites in the system. At a similar overpotential, but on the opposite side of the volcano, lie three points: The two Ni-Ni bridge sites and the AC2 point following the ruthenium pathway. These should all be considered efficient active sites of the surface, without the expectation of them being occupied before the reaction starts (due to them being on the weak side of the volcano). Take note of the large change in activity associated with a change of mechanism for AC2. The conventional pathway places this point in the bottom left of the volcano where it is not expected to be very efficient, whereas the ruthenium pathway places it at the top with IrO 2 as is also seen experimentally. Based on these results it is expected that the first sites to activate are the Ni-Ni site and the ruthenium CUS sites of the system. By increasing the electrode potential a point can be reached where a lot of Ru-Ni sites become active. This echoes the sentiment from the initial rough analysis of surface oxygen binding energies. In the bottom of the plot is found the BCD8 site associated with the "popout" mechanism. This placement implies that the mechanism isn't particularly relevant and that this subsurface oxygen is therefore not expected to evolve under normal working conditions. These findings paint a picture of LOER being dependent on Ru-Ni bridge sites in this system. It can therefore be expected that an occurrence of Ru-Ni bridge sites is associated with the extent of LOER. It can also be expected that this LOER tendency is activatable by elevated electrode potentials. From this surface analysis we can predict the composition at which we would expect to see the most LOER, as that would be the composition which maximizes the number of Ru-Ni bridge sites. The Ru 1-x Ni x O 2 system has previously been experimentally characterized by Petrykin et al. . They found that the nickel atoms tend to cluster together, and the exact method of clustering depends on x. For x < 5% nickel atoms tend to cluster in groups of three, in zig-zag patterns excluding the shortest metal-metal distance for neighbors. Thus the nickel clusters across the surface from bridge site to CUS site (or into the surface), however it does not cluster along the CUS or bridge lines. This type of clustering has been illustrated in fig. . On the other hand, for x > 10 %, nickel begins clustering as shear planes along the [121] direction. With this in mind, two simple models for the prediction of LOER active site density as a function of nickel concentration can be set up. One for low nickel content (x < 5%) and one for high nickel content (x > 10%).