| AVS 56th International Symposium & Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS3-TuA |
| Session: | Catalysis: Mechanisms & Morphology |
| Presenter: | T. Anniyev, Stanford Synchrotron Radiation Lightsource |
| Authors: | T. Anniyev, Stanford Synchrotron Radiation Lightsource S. Kaya, Stanford Synchrotron Radiation Lightsource H. Ogasawara, Stanford Synchrotron Radiation Lightsource S. Koh, University of Houston P. Strasser, University of Houston M. Toney, Stanford Synchrotron Radiation Lightsource A. Nilsson, Stanford Synchrotron Radiation Lightsource |
| Correspondent: | Click to Email |
A key role in the activity of transition metal catalysts is the degree of interaction of metal d-bands with the adsorbed atoms/molecules [1]. It has been suggested that d-band center is a single effective measure of this interaction [2]. In this work we demonstrate how strain induced electronic structure changes can be used to tune the catalytic activity of the Oxygen Reduction Reaction (ORR). The limiting factor in the performance of the Pt-based PEM fuel cells is the low rate of the ORR taking place at the cathode. It has recently been shown that electrochemically leached PtCu catalysts, which have strained Pt rich shell due to dissolution of Cu, exhibit uniquely high reactivity for this reaction [3] . Using a surface science approach we have investigated the electronic structure effect in the enhanced ORR activity using Pt monolayers epitaxially grown on Cu(111) as a model system. We show that compressive strain and host substrate-induced changes in the Pt d-band center are responsible for the changes in chemisorption strength of adsorbed oxygen. Electronic nature of chemisorbed oxygen atoms on strained Pt monolayers has been investigated by probing oxygen projected density of states below and above the Fermi level using X-ray emission spectroscopy (XES) and X-ray absorption spectroscopy (XAS), respectively. Combined oxygen K-edge XAS and XES results of oxygen on strained Pt monolayers show lowering of the adsorbate projected density of states and a complete filling up of antibonding states above Fermi level indicative of weakened metal-oxygen bond relative to that of oxygen on Pt(111). The weakening of the metal-oxygen bond is correlated with the broadening and lowering of the Pt d-band probed by valence band X-ray photoemission spectroscopy (XPS). The observed results are explained in terms of the d-band model.
References
[1] B. Hammer and J. K. Norskov, Theoretical surface science and catalysis—calculations and concepts, Adv. Catal. 45, 71 (2000).
[2] G.A. Somorjai, Introduction to Surface Chemistry and Catalysis (John Wiley & Sons, New York, 1994).
[3] S. Koh and P. Strasser, Electrocatalysis on bimetallic surfaces: Modifying catalytic reactivity for oxygen reduction by voltammetric surface de-alloying, J. Am. Chem. Soc., 129 (42), 12624-12625 (2007).