An Evaluation of the Ethanol Oxidation Activity of Ternary Pt-Rh-SnO2 catalysts Prepared from the Vapor Phase

Wednesday, May 14, 2014: 11:00
Bonnet Creek Ballroom II, Lobby Level (Hilton Orlando Bonnet Creek)
J. M. Roller (Department of Materials Science and Engineering at the University of Connecticut, Center for Clean Energy Engineering), H. Yu (Center for Clean Energy Engineering, Department of Chemical and Biomolecular Engineering at the University of Connecticut), M. Li, S. Bliznakov, M. Vukmirovic, R. Adzic (Chemistry Department, Brookhaven National Laboratory), and R. Maric (Department of Chemical and Biomolecular Engineering at the University of Connecticut, Department of Materials Science and Engineering at the University of Connecticut)
Ethanol holds promise as a non-toxic, transportable, energy dense (8kWh/kg), and fuel that, unlike hydrogen, is amenable to use in the existing fuel infrastructure. However, slow oxidation kinetics and incomplete CO2 formation, indicating unbroken C-C bonds at practical potentials, limit usage in a fuel cell. Incomplete formation of CO2, a complete 12 electron transfer, leads to the formation of adsorbed intermediates such as CO, acetaldehyde, and acetic acid. These intermediates can poison the catalyst surface leading to a loss in cell efficiency.  The use of Pt/Rh/Sn ternary catalysts has proven promising owing to bi-functional, electronic, and synergistic effects between the constituents. The role of Rh is to cleave the C-C bond of ethanol, SnO2provides the OH species to oxidize intermediates (freeing the Pt and Rd sites), and Pt is for ethanol dehydrogenative adsorption [1]. Typical synthesis methods include polyol [2], Bönneman [3], co-impregnation-reduction [4], or cation-adsorption-reduction-galvanic displacement [5] techniques.

 Previous flame-based deposition of catalysts for ethanol oxidation have focused on Pt-Sn combinations and found that 10 wt.% Sn showed the best onset potential (~0.3V vs RHE) and largest oxidation peaks in 0.5 M H2SO4and 1 M ethanol at 1 mV/s [6].

 Reactive spray deposition technology (RSDT) has been developed by Maric et al. to produce nanoparticles in vapor phase for catalysts comprised of Pt [7,8], IrxPt1-xO2-y, and IrxRu1-xO2-y [9]. In this work we extend recent studies on Pd-Ru and Pd cores made by the RSDT process, with subsequent Pt monolayer attachment by galvanic displacement, to the ternary Pt/Rh/Sn system. Elemental ratios of 3:1:3 and 3:2:3 are examined for their performance toward ethanol oxidation.  Figure 1 shows the nodular morphology of Pt/Rh/Sn (3:2:3) as grown on a gas diffusion layer along with the XEDS elemental mapping. Strategies for electrode activation using potential cycling in HClO4, ethanol and CO stripping are discussed. Figure 2 is a plot of the CV after various pre-treatment approaches. The performance toward ethanol oxidation at room temperature and 60oC will be discussed in respect to chemical composition. A representative linear sweep voltammogram is shown in Figure 3.  Infrared reflection-absorption spectroscopy (IRRAS) is explored to detail the EOR mechanism. Microscopy studies of the structure and chemical composition are presented.


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