Pt "Monolayer"� Electrocatalysts Revisited: Structure, Lattice Geometry Effects, and Ethanol Oxidation Activity of Pt on Au

Effective utilization of the high energy density of ethanol as a fuel for polymer electrolyte fuel cells is contingent upon complete oxidation of ethanol to carbon dioxide. Major problems associated with the development of electrocatalysts for ethanol oxidation are the high content of Pt and partial oxidation of ethanol to acetaldehyde and acetic acid instead of complete oxidation to carbon dioxide via the 12 electron process. Monolayers of Pt on Au have been proposed and reported¹ to be beneficial for EtOH oxidation and possibly for C-C bond splitting. We address this issue with atomic scale microscopy and spectroscopy.

In this report, Pt atomic layers supported on both well-defined, extended Au(111) and Au NPs  were studied as electrocatalysts for ethanol oxidation reaction (EOR)². The catalyst were prepared using galvanic displacement methods using Pt(II) and Pt(IV) precursors. Electrochemical testing of these electrocatalysts showed that Au@Pt(II) had substantially higher activity towards EOR than Au@Pt(IV). The atomic scale structure of the resulting Pt layers on Au will be studied using HAADF-STEM-EDX elemental mapping as well as depth resolved XPS. Evidence is provided that the so-called Pt “monolayer” catalysts actually consist of 2-4 atom layers of Pt, often aggregated in small clusters. The effect of Pt cluster sizes on the Au surface and the tensile strain on Pt due to the underlying Au and their effect on EOR will be discussed. Using in-situ FTIR we also studied the catalytic EtOH activity of the catalysts and their ability to perform C-C bond splitting.

1.            Li, M.; Liu, P.; Adzic, R. R., Platinum Monolayer Electrocatalysts for Anodic Oxidation of Alcohols. J. Phys. Chem. Lett. 2012, 3, 3480-3485.

2.            Loukrakpam, R.; Yuan, Q. Y.; Petkov, V.; Gan, L.; Rudi, S.; Yang, R. Z.; Huang, Y. H.; Brankovic, S. R.; Strasser, P., Efficient C-C bond splitting on Pt monolayer and sub-monolayer catalysts during ethanol electro-oxidation: Pt layer strain and morphology effects. Phys. Chem. Chem. Phys. 2014, 16, 18866-18876.