The performance of H-2/O-2 proton exchange membrane fuel cells (PEMFCs) fed with CO-contaminated hydrogen was investigated for anodes with PdPt/C and PdPtRu/C electrocatalysts. The physicochemical properties of the catalysts were characterized by energy dispersive X-ray (EDX) analyses, X-ray diffraction (XRD) and "in situ" X-ray absorption near edge structure (XANES). Experiments were conducted in electrochemical half and single cells by cyclic voltammetry (CV) and I-V polarization measurements, while DEMS was employed to verify the formation of CO2 at the PEMFC anode outlet. A quite high performance was achieved for the PEMFC fed with H-2 + 100 ppm CO with the PdPt/C and PdPtRu/C anodes containing 0.4 mg metal cm(-2), with the cell presenting potential losses below 200 mV at 1 A cm(-2), with respect to the system fed with Pure H-2. For the PdPt/C catalysts no CO2 formation was seen at the PEMFC anode outlet, indicating that the CO tolerance is improved due to the existence of more free surface sites for H-2 electrooxidation, probably due to a lower Pd-CO interaction compared to pure Pd or Pt. For PdPtRu/C the CO tolerance may also have a contribution from the bifunctional mechanism, as shown by the presence of CO2, in the PEMFC anode outlet. (c) 2008 Elsevier Ltd. All rights reserved.