Novel Ir@Pt Core@Shell Nanoparticles As Catalysts for Ethanol Oxidation

Ethanol is a promising fuel for transportation applications, given its low toxicity and easy access from feedstock fermentation. However, the combustion of ethanol to regain the stored energy is highly inefficient and thus a non-combustion process, such as the electrochemical oxidation of ethanol in a fuel cell, is desirable for utilizing the stored energy. To achieve high conversion efficiencies, an appropriate catalyst for ethanol oxidation must be developed. While Pt is a good material for this purpose, it is prone to poisoning by strongly adsorbed intermediates, e.g., CO. To address these shortcomings, Pt can be nanostructured and combined with other metals, resulting in superior activity and longer lifetimes. In the present work, Ir core@Pt shell nanoparticles (NPs) were synthesized, with varying Pt shell coverages (less than one monolayer), ensuring that some Ir is exposed and thus allowing the bifunctional effect [1], electronic [2], and strain effects [3] to all play a role in the catalysis of the ethanol oxidation reaction. The core@shell NPs were synthesized using the polyol method [4], producing a core that was ca. 3 nm in diameter and then loaded (10 mass %) onto Vulcan Carbon powder. These catalysts were then characterized by wavelength-dispersive X-ray spectroscopy (WDS) and thermogravimetric analysis to determine the relative percentage of each metal present in each nanoparticle and to confirm the metal loading onto the carbon, respectively, while TEM analysis confirmed the expected NP size and distribution. The electrocatalytic activity of these materials was evaluated using a three electrode system, all in 0.5 M H2SO4 + 0.01 - 1 M ethanol at room temperature. Overall, it is shown that these Ir core@Pt shell NPs are notably more active than Pt NPs of the same size and also produced using the polyol method. The activity of the catalysts increases with ethanol concentration, but less than linearly, and sweep rate studies revealed the presence of electroactive surface-bound reaction intermediates. The stability of the catalysts has also been investigated using cyclic voltammetry and chronoamperometry experiments. By studying the effect of Pt shell coverage on the Ir core NPs, the mechanism by which Ir enhances the activity of Pt during ethanol oxidation is now being determined. References: El Sawy, E. N.; Molero, H. M.; Birss, V. I. Electrochimica Acta (EAST13-0480) 2013. Chen, Y. M.; Yang, F.; Dai, Y.; Wang, W. Q.; Chen, S. L. Journal of Physical Chemistry C 2008, 112, 1645-1649. Zhang, X. T.; Wang, H.; Key, J. L.; Linkov, V.; Ji, S.; Wang, X. L.; Lei, Z. Q.; Wang, R. F. Journal of The Electrochemical Society 2012, 159, B270-B276. Alayoglu, S.; Eichhorn, B. Journal of the American Chemical Society 2008, 130, 17479- 17486.