In addition, different structural properties will also have an effect on the ORR selectivity (H 2 O vs. H 2 O 2 formation), which can be deduced from the yields. So far, H 2 O 2 yields on Ru electrodes / catalysts were rarely reported in the literature, in particular not for single crystal electrodes. For carbon-supported Ru catalysts, Hara et al. reported H 2 O 2 yields in the range of a few percent in 0.5 M H 2 SO 4 for potentials < 0.6 V, with an onset of the ORR at 0.7 V. Bron et al. reported yields of approximately 22% close to the onset potential of the ORR in 0.5 M H 2 SO 4 , which dropped to around 5% close to the potential for hydrogen adsorption and evolution. Similar values and trends were obtained for the Ru(pc) elec-trodes presented in Section S5 of the SI.Based on the pronounced differences in the yields reported so far for different types of Ru(pc) and Ru(0001) single crystals (this work) substantiates the assumption that the selectivity strongly depends on the structural properties of the Ru electrode.