Preparation and characterizations of platinum electrocatalysts supported on thermally treated CeO₂–C composite support for polymer electrolyte membrane fuel cells

Highlights: • CeO₂–C composite support was prepared by a sol-gel approach with an average particle size of 2.5 nm. • The crystallinity of ceria was tuned by thermal treatment from 400 °C to 600 °C. • Well correlated Pt–ceria interaction was found for the Pt electrocatalysts in PEMFCs. - Abstract: 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 N₂ 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 °C for CeO₂–C, and Pt/CeO₂–C-550 demonstrated the highest mass activity of 0.71 A mg⁻¹ for methanol oxidation (∼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 H₂/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 °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