Pt-Sn-Eu/C Catalysts: Application of Rare Earth Metals as Anodes in Direct Ethanol Fuel Cells

Pt-Sn-Eu catalysts were synthesized by modified polyol method, evaluated for the ethanol oxidation reaction (EOR), and compared to commercial Pt/C and Pt-Sn/C catalysts. The catalysts were electrochemically characterized in both three-electrode and fuel cell setups. X-ray diffraction measurements indicated some degree of Pt-Sn alloying in the Pt-Sn-Eu/C catalysts, and mean crystallite sizes between 2.3-3.3 nm, while X-ray photoelectron spectroscopy measurements showed the presence of Pt and Sn in both metallic and oxide form, and rare earth metals in the form of mixed oxides. Adding tin and europium promoted filling of the Pt 5d band, as confirmed by X-ray absorption. The electrochemical characterization showed a higher oxidation current density and lower oxidation onset potential for the ternary Pt-Sn-Eu materials compared with the commercial catalysts, in both the three-cell and fuel cell tests. High performance liquid chromatography measurements indicating that the main products of ethanol oxidation were acetaldehyde and acetic acid; a low concentration of CO2 was also detected. The improved ethanol oxidation efficiency for the Pt-Sn-Eu/C catalysts can be explained by the Sn/Eu-Pt electronic effect, because it weakens the adsorption of intermediate products by Pt, and favors the bifunctional EOR mechanism, as europium oxide renders oxygenated species available at lower potentials. (AU)