Pt electrocatalysts used in PEM fuel cells are easily poisoned by small amounts of carbon monoxide in hydrogen-rich fuel gas streams [1]. It has been demonstrated that the CO-tolerance of Pt catalysts can be improved by the addition of a second metal due to either a bifunctional mechanism or an electronic effect [2]. The single atom alloys (SAAs) consist of Pt atoms exclusively in dispersed, isolated sites [3] which only allow the weaker atop adsorption of CO that improves the CO tolerance of the Pt metal through a geometric effect.
Here we have investigated the CO tolerance performance of Pt/Cu SAAs. Nanoparticles of Pt/Cu SAAs were prepared by colloidal synthesis and subsequent galvanic replacement of Cu for trace amounts of Pt [4]. The SAA geometry was found to enhance CO tolerance during H2 activation and hydrogenation of acetylene. The H2-D2 exchange reaction was used to probe the H2 activation activity of the Pt/Cu SAA and Pt monometallic catalyst. We show that the CO in the gas phase exerts a significantly smaller poisoning effect on the hydrogenation activity of Pt/Cu SAA compared to the Pt monometallic catalyst. The preparation, reactivity, and characterization of the SAA nanoparticles with IR, X-ray photoelectron spectroscopy, electron microscopy and X-ray absorption techniques will be presented. Using scanning tunneling microscopy (STM) and temperature programmed desorption/reaction (TPD/R), we show the atomic scale structure of these systems and demonstrate that Pt-Cu(111) SAAs bind CO much weaker than contiguous Pt.
References
[1] Wakisaka, M. et al. Electronic Structures of Pt-Co and Pt-Ru Alloys for CO-Tolerant Anode Catalysts in Polymer Electrolyte Fuel Cells Studied by EC-XPS. J. Phys. Chem. B 110, 23489-23496 (2006).
[2] Pereira, L. G. et al. Investigation of the CO tolerance mechanism at several Pt-based bimetallic anode electrocatalysts in a PEM fuel cell. Electrochim. Acta 54, 1992-1998 (2009).
[3] Lucci, F. R., Lawton, T. J., Pronschinske, A. & Sykes, E. C. H. Atomic scale surface structure of Pt/Cu(111) surface alloys. J. Phys. Chem. C 118, 3015–3022 (2014).
[4] Boucher, M. B. et al. Single Atom Alloy Surface Analogs in Pd0.18Cu15 Nanoparticles for Selective Hydrogenation Reactions. Phys.Chem.Chem.Phys. 15, 12187-96 (2013).
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