Carbon supported Ru@Pt/C catalysts with a Ru-rich core and Pt-rich shell structure are prepared by the solid-state diffusion of Pt and Ru via high-temperature heat treatment. In general, heat treatment at high temperatures causes a sintering effect that leads to the aggregation of nanoparticles into larger particles. Carbonized polydopamine is introduced as a protective coating to inhibit the movement of particles during the high-temperature heat treatment. This carbon layer, which inhibits the particle grain growth, should, however be removed after heat treatment because it blocks the active sites required for the hydrogen oxidation reaction. In this study, ozone treatment at room temperature for 15 min is used to effectively remove the carbon layer on the catalyst surface. Energy-dispersive X-ray spectroscopic line scan profile and X-ray photoelectron spectroscopic analysis confirm that the PtRu/C catalyst has a Ru-rich core and Pt-rich shell structure. From CO stripping voltammetry and polymer electrolyte membrane fuel cell tests using CO containing H-2 gas, the core-shell structured PtRu/C alloy formed by high-temperature annealing is demonstrated to have higher tolerance to CO poisoning than PtRu/C catalysts synthesized by co-deposition via the polyol method. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.