Two series of proton exchange membrane fuel cell (PEMFC) catalysts have been synthesized by modifying two parameters, the reduction-step length and the carbon-black surface chemistry. The scope and applicability of conventional physical techniques for their structural characterization, such as X-ray diffraction or transmission electron microscopy, are compared with those of others involving chemical processes such as temperature-programmed oxidation, hydrogen chemisorption, or temperature-programmed desorption. The presented results show that these latter techniques provide valuable complementary information for the characterization of these catalysts. The influence of surface-diffusion processes on PEMFC catalyst properties is discussed in light of the presented characterization results. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3059169] All rights reserved.