Structure and surface characteristics of carbon-supported PtCo cathode electro-catalysts were investigated to evaluate their performance and resistance to degradation under high temperature (similar to 110 degrees C) operation in a polymer electrolyte membrane fuel cell (PEMFC). Two different thermal treatments were investigated, i.e. 600 degrees C and 800 degrees C causing the occurrence of a disordered face-centered cubic (fcc) structure and a primitive cubic ordered (L1(2)) phase. A specific colloidal preparation route and a carbothermal reduction allowed to obtain a similar mean crystallite size. i.e. 2.9 and 3.3 nm for the catalysts after the treatment at 600 degrees C and 800 degrees C, as well as a suitable degree of alloying. Both electrocatalysts were subjected to the same pre-leaching procedure to modulate the surface characteristics. The surface properties were investigated by X-ray photoelectron spectroscopy (XPS) and low-energy ion scattering spectroscopy (LE-ISS,3He(+) at 1 kV). A Pt segregation in the outermost surface layers and similar electronic properties for the materials were observed. Both catalysts showed good performance under PEMFC operation; however, the catalyst characterised by the disordered fcc structure performed slightly better at low temperature (80 degrees C) and full humidification; whereas, the primitive cubic ordered structure catalyst showed superior characteristics both in terms of performance and stability at high temperature (110 degrees C) and low R.H. These operating conditions are more relevant for automotive applications. The enhanced stability of the catalyst characterised by primitive cubic ordered structure was attributed to the growth of a stable Pt-oxide layer during operation at high temperature and low R.H. hindering sintering and dissolution processes at the catalyst surface. (C) 2012 Elsevier B.V. All rights reserved.