To probe the influence of the position of an O-vacancy underneath the Ru nanorod, we first calculated the CO adsorption energy on systems with a single isolated O-vacancy at the interface perimeter, under the edge of Ru nanorod (the 1 st and 3 rd row of oxygen atoms in Figure ) and away from the perimeter sites (the 2 nd row oxygen atoms in Figure ). While the O-atoms in the 1 st and 3 rd rows appear symmetric in Figure , their interactions with the Ru nanorod differ due to the mismatch of the Ru nanorod and the support lattices. The most favorable sites for O-vacancy formation, as given by the Ovacancy formation energy (see Figure ), are the 1i site for the 1 st row, the 4i site for the 2 nd row, and the 7i site for the 3 rd row. Therefore, we calculated the CO adsorption energies on the different adsorption sites ('top layer (terrace)', 'top layer (edge)', 'middle layer', 'interface (i)', and 'interface (ii)' sites) for Ru/ZrO2-x systems with a single O-vacancy at the 1i site (pink bar), at the 4i site (blue bar), and at the 7i site (orange bar), respectively (see Figure ). For comparison, we also included CO adsorption energies on the fully oxidized Ru/ZrO2 model system (grey bar), using the same Ru adsorption sites. In our previous work, The trend in these CO adsorption energies is illustrated in Figure and listed in Table .