Previously we had reported that the formation of O-vacancies is accompanied by a partial reduction of the neighboring Zr ions and, in the presence of the Ru nanorod, by a less pronounced reduction of the Zr ions and an electron transfer from the support to the Ru nanorod. formation energy (Figure ). The correlation is even more obvious when plotting the Ruinduced lowering of the O-vacancy formation energy Evac rather than the O-vacancy formation energy itself versus the charge transfer from the support to the Ru nanorod upon O-vacancy formation (Figure ). In this case, effects from structural differences between the different oxygen sites in the Ru-free ZrO2 surface should be largely cancelled. Indeed, except for the data points 2i, 8i and 9i, there is a strict correlation between the Ru-induced lowering of the Ovacancy formation energy and the charge transfer, which is indicated by the full line (see also the following discussion).