ABSTRACT:In situ electrochemical X-ray absorption fine structure (XAFS) measurements were performed at the Pt L 3 and Ce L 3 edges of the Pt−CeO x /C catalyst, which was prepared by a combined process of precipitation and coimpregnation methods, as well as at the Pt L 3 edge of the conventional Pt/C catalyst in oxygen-saturated H 2 SO 4 solution to clarify the role of CeO x in the reduction of the overpotential for the oxygen reduction reaction (ORR) at the Pt−CeO x nanocomposite compared with the conventional Pt/C catalyst. XAFS measurements clearly show that the enhancement of ORR activity is attributed to the inhibition of Pt oxide formation by the CeO x layer, of which Ce 3+ was oxidized to Ce 4+ instead of Pt at the Pt oxide formation potential.

To understand the ceria promotion effect of Pt-CeO(2)/C catalysts on methanol oxidation, microstructural and metal-oxide interactions of Pt-CeO(2)/C catalysts with an atomic ratio of Pt/Ce between 0.14 and 1.4 were systematically examined using high-resolution transmission electron microscopy and electron energy loss spectroscopy (EELS). With an increasing Pt content in the catalysts, Pt particles gradually invaded into the ceria supports and decoration on Pt particles was observed. Simultaneously, the morphology of the supports was dramatically modified with nanocrystalline and amorphous ceria formed between and/or around the Pt particles. It reveals that the Pt-ceria interaction could take place in the catalysts and the influence of the interaction was enhanced with an increasing Pt/Ce ratio. The EELS study demonstrated that the strong Pt-ceria interaction was related to the redox reaction between Pt and ceria. Experimental results also suggested that the strong interaction between Pt and ceria could contribute to the promotion effect of ceria on the oxidation of methanol.

No abstract