In this paper, we present experimental results on the preparation and the electrochemical characterization of PtxCoy electrocatalytic particles with homogeneous composition, modeled by Franco et al. [J. Electrochem. Soc., 156, B410 (2009)]. Preparation is made through the direct liquid injection metallorganic chemical vapor deposition technique previously developed at CEA, and electrochemical analysis is carried out by using a rotating disk electrode and membrane-assembled gas diffusion electrode. Degradation structural changes are characterized by using transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Optimal Co compositions are identified for better oxygen reduction reaction activity and durability, validating the modeling studies. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3385000] All rights reserved.