The Pt-modified Ru(0001) single-crystal electrodes used in this work were prepared and characterized by STM under UHV conditions at the Institute of Surface Chemistry and Catalysis at Ulm University (Ulm, Germany). The electrochemical DEMS characterization was performed in Ulm and the combined electrochemical and SXRD measurements at the ID03 beamline of the European Synchrotron Radiation Facility (ESRF, Grenoble, France). Where necessary, we indicate facility-specific experimental details.