Interaction of carbon monoxide with CNx catalysts was investigated using pulse chemisorption, DRIFTS, and cyclic voltammetry techniques. Pulsed chemisorption experiments showed no CO uptake over the CNx catalysts. Cyclic voltammetry and potential hold studies showed carbon monoxide not to have any electrocatalytic interaction with nitrogen-doped graphite surfaces and not to have any poisoning effect for the oxygen reduction reaction. This is in contrast to the preferential adsorption of CO in the presence of oxygen on ORR sites of Pt catalysts, inhibiting the oxygen reduction activity drastically. Cyanide poisoning experiments performed using KCN showed no activity loss for CNx, while Pt/VC catalysts showed significant deactivation. These studies suggest that it is unlikely for coordinated metal sites to have significant contribution to the oxygen reduction reaction in CNx catalysts. (C) 2011 Elsevier B.V. All rights reserved.