Ethanol is a promising fuel for low-temperature direct fuel cell reactions due to its low toxicity, ease of storage and transportation, high-energy density, and availability from biomass. However, the implementation of ethanol fuel cell technology has been hindered by the lack of low-cost, highly active anode catalysts. In this paper, we have studied Iridium (Ir)-based binary catalysts as low-cost alternative electrocatalysts replacing platinum (Pt)-based catalysts for the direct ethanol fuel cell (DEFC) reaction. We report the synthesis of carbon supported Ir(71)Sn(29) catalysts with an average diameter of 2.7 ± 0.6 nm through a "surfactant-free" wet chemistry approach. The complementary characterization techniques, including aberration-corrected scanning transmission electron microscopy equipped with electron energy loss spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy, are used to identify the "real" heterogeneous structure of Ir(71)Sn(29)/C particles as Ir/Ir-Sn/SnO(2), which consists of an Ir-rich core and an Ir-Sn alloy shell with SnO(2) present on the surface. The Ir(71)Sn(29)/C heterogeneous catalyst exhibited high electrochemical activity toward the ethanol oxidation reaction compared to the commercial Pt/C (ETEK), PtRu/C (Johnson Matthey) as well as PtSn/C catalysts. Electrochemical measurements and density functional theory calculations demonstrate that the superior electro-activity is directly related to the high degree of Ir-Sn alloy formation as well as the existence of nonalloyed SnO(2) on surface. Our cross-disciplinary work, from novel "surfactant-free" synthesis of Ir-Sn catalysts, theoretical simulations, and catalytic measurements to the characterizations of "real" heterogeneous nanostructures, will not only highlight the intriguing structure-property correlations in nanosized catalysts but also have a transformative impact on the commercialization of DEFC technology by replacing Pt with low-cost, highly active Ir-based catalysts.

Alternative Electrocatalysts for the Ethanol Oxidation Reaction. -Carbon supported Ir71Sn29 catalysts with an average diameter of 2.7 nm are prepared from mixtures of SnCl2, IrCl3, Sn, ethylene glycol, and water (Ar flow, 130°C, 2 h) followed by mixing the as made Ir71Sn29 particles with carbon black (magnetic stirring, 20°C, 1 h). The samples are characterized by HRTEM, STEM, EELS, XRD, XPS, XAS, EXAFS, electrochemical measurements, and DFT calculations. The catalyst particles consist of an Ir-rich core and an Ir-Sn alloy shell with SnO2 present on the surface, Ir/Ir-Sn/SnO2. The Ir71Sn29/C heterogeneous catalyst exhibits high electrochemical activity toward the ethanol oxidation reaction compared to commercial Pt/C, PtRu/C, and PtSn/C catalysts. The superior electro-activity is related to the high degree of Ir-Sn alloy formation as well as the existence of nonalloyed surface SnO2. These results may have significant impact on direct ethanol fuel cell technology by completely replacing Pt with an alternative low-cost, highly active Ir-based nanocatalyst. -(DU, W.; WANG, Q.; SAXNER, D.; DESKINS, N. A.; SU, D.; KRZANOWSKI, J. E.; FRENKEL, A. I.; TENG*, X.; J. Am. Chem. Soc. 133 (2011) 38, 15172-15183, http://dx.