Finally, we would like to note that these arguments and considerations refer to the energetics of the O-vacancy formation process, where additional kinetic barriers are not included. Most important, kinetically the exchange at the perimeter of the interface will be favored as compared . In most of the cases, the energy cost for the O-vacancy formation in the cluster is lower than or equal to that for the formation of an isolated vacancy, but the differences are generally small. They are most pronounced for the energetically most costly O-vacancy formation at the 3i and 5i sites, where the differences are 0.38 and 0.44 eV, respectively. Hence, promotional effects induced by the presence of neighboring O-vacancies are generally small. A similar trend is also observed for the formation of an O-vacancy in a growing cluster in the absence of a Ru nanorod (see Table ). The only exception in these sequences is the formation of the third O-vacancy at the 3i site in a cluster, which is by 0.83 eV less costly than that of an isolated vacancy at that site. As before, we also plotted the relation between the O-vacancy formation energy Evac and the charge transfer from the support to the Ru nanorod upon O-vacancy formation in the growing O-vacancy cluster (blue squares in Figure ) and the relation between Ru-induced lowering of the O-vacancy formation energy Evac and the above charge transfer (blue squares in Figure ). For comparison, we also included the corresponding data for individual O-vacancies from Figure and 3c (black dots). In all cases, the additional charge transfer upon formation of an O-vacancy in a growing O-vacancy cluster is smaller than that for the individual vacancy at the same location, which can be understood based on depolarization effects. (Note that this comparison is only possible for the vacancies VO(2i) -VO(5i)). Except for this depolarization effects and the resulting shift to lower charge transfer, the data points seem to fit reasonably well to the linear correlations derived in Figure and 3c, which are included as red lines.