Solid polymeric fuel cells (SPFC) are devices that are able to convert chemical energy into electric energy continuously without any ambient pollution. The electrodes of this type of cells are layered structures, composed of a carbon support, a diffusive layer and a catalytic layer, usually platinum clusters dispersed on amorphous carbon microparticles, whose properties, at atomic and molecular level, determine the catalytic behaviour. In this work, microstructural and compositional properties of the catalytic layer are studied by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Firstly the electronic properties of Pt clusters are compared with those of Pt bulk and the different response to the photoemission process is evidenced. Moreover, changes in the Pt photoemission spectral features from electrodes subjected to different treatments are correlated with particle size variation.