The main objectives of this study are to investigate the carbon monoxide (CO) poisoning and a mitigation method of high-level CO in a platinum (Pt) catalyst layer using hydrogen (H-2)/CO mixture as the inlet fuel. Two separate levels of poisoning, 1000 and 10,000 ppm CO at the anode fuel, are considered and investigated in detail. For this purpose, a one-dimensional transient model is developed including the diffusion of hydrogen and carbon monoxide, the conservation of adsorbed species, and ionic and electronic charges. As a result of CO poisoning, oscillations in overpotential and coverage of adsorbed species are observed for 1000 ppm CO level, while the similar situation is not detected for 10,000 ppm CO. Hence, the behavior of oscillations throughout the catalyst layer thickness, and the reasons are explored for the lower concentration case. For 10,000 ppm CO, a mitigation technique, in which current density is pulsed from 0.1 to 2.5 A/cm(2) for a period of time, is performed in order to remove the adsorbed CO from the Pt sites. It is concluded that up to 92% of CO coverage within the catalyst layer can be removed, and 70% of the catalyst layer length is determined to be completely CO-free following the application of current pulsing. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.