a b s t r a c t The reaction mechanism of heterogeneous CO oxidation on yttria-stabilized zirconia (YSZ), frequently used as electrolyte in solid oxide fuel cell (SOFC) composite anodes, was investigated employing density functional theory (DFT). The results demonstrate the possibility for an Eley–Rideal type CO oxidation reaction on the electrolyte surface without the need for a metallic catalyst if the vacant sites of YSZ are filled by externally supplied oxygen, either by dissociative adsorption of gaseous O 2 or via bulk oxy-gen atoms delivered by the SOFC cathode. Our results are consistent with the findings of recent experi-ments [J. Electrochem. Soc. 158 (2011) B5]. Ó 2012 Elsevier B.V. All rights reserved.