Syntheses of supported Pt/C nanoparticles via a water-in-oil microemulsion method are described, including some variations in the surfactant removal step (chemical reagents, thermal treatment, washing procedure, surfactant batch, etc.). Their influence on the microstructure and on the electrochemical activity is evaluated. X-ray diffraction (XRD) and transmission electron microscopy (TEM) allow domain size distributions and corresponding domain sizes (L-v and D-m) to be evaluated. Thermal treatment under reductive atmosphere at only 200 degrees C leads to the sintering of the platinum particles. Under H-2 3% in He atmosphere conditions (close to fuel cell working conditions) it is shown that L-v increased with temperature following two kinetics according to the temperature range (25-200 degrees C and 200-500 degrees C). Change of the surfactant causes large differences in L-v. For catalysts prepared with the same precursor batch, very close L-v are obtained, whereas electrochemical measurements (hydrogen adsorption-desorption and CO stripping) display marked differences. (c) 2007 Elsevier B.V. All rights reserved.