An Evaluation of the Ethanol Oxidation Activity of Ternary Pt-Rh-SnO2 catalysts Prepared from the Vapor Phase
Authors: Roller Justin Michael , Yu Haoran , Li Meng , Bliznakov Stoyan , Vukmirovic Miomir , Adzic Radoslav , Maric Radenka 
Published: February 2020

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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