A sol-gel approach was used to synthesize highly dispersed carbon-supported ceria composite support (CeO2-C) having an average particle size of 2.5 nm with sodium citrate as a ligand. The CeO2-C composite was then heated in N-2 atmosphere at different temperatures to induce crystallinity variation. Pt electrocatalysts were prepared by the conventional ethylene glycol method using the thermally treated composite support (CeO2-C-T) and then characterized by X-ray diffraction and transmission electron microscopy. Electrochemical evaluations of Pt/CeO2-C-T catalytic activity were performed for methanol oxidation and oxygen reduction reactions. An optimized heating temperature was found at 550 degrees C for CeO2-C, and Pt/CeO2-C-550 demonstrated the highest mass activity of 0.71 A mg(-1) for methanol oxidation (similar to 100% that of Pt/C-JM from Johnson Matthey) and 17 mV more positive shift of the half-wave potential for oxygen reduction relative to that of Pt/C-JM. The maximum power density of the membrane electrode assembly (MEA) with Pt/CeO2-C-550 cathode catalyst in a H-2/air polymer electrolyte membrane fuel cell was 678 mW cm(-2), which was 7% higher than that of MEA prepared with Pt/C-JM under identical operating conditions. Heating CeO2-C at 550 degrees C induced increased crystallinity without sacrificing particle agglomeration, which was beneficial for Pt dispersion (reduced particle size). Meanwhile catalytic activity was further enhanced because of Pt-metal oxide interactions and the known oxygen buffer capability of CeO2. (C) 2014 Elsevier Ltd. All rights reserved.