The promoting effect of incorporation of carbon atoms into the crystalline lattice of palladium on its electrocatalytic performance for the hydrogen oxidation reaction (HOR) and CO tolerance was found, for the first time, with the PdCx/C catalysts prepared via (1) treatment of the pre-deposited Pd particles with C2H4 at 300 degrees C and (2) successive calcination/reduction of a Pd/C precursor in flowing Ar and H-2 at 250 degrees C. The formation of the interstitial PdCx solutions was confirmed by means of X-ray diffraction, high resolution transition electron microscopy and a set of electrochemical methods. The HOR on the as-prepared and CO-poisoned PdCx/C catalysts was studied using rotating disk electrode. For the catalysts prepared without the use of specially added carbon source (route 2), the correlation between the microstructure of a carbon support and the catalyst activity for the HOR is observed: the structurally more disordered supports give rise to the more active catalysts. The most active PdCx/C catalysts demonstrate up to a 2.5-fold increase in the exchange current density of the HOR and a rise of about 20-fold in the hydrogen oxidation current density in the presence of 1100 ppm CO comparing to the Pd/C catalysts. (C) 2011 Elsevier B.V. All rights reserved.