A wide array of studies on platinum have been performed due to the central role it plays in hydrogenation reactions [1-5]. In a previous study, we found very weak or no vibrationally assisted sticking effect for H2 dissociative adsorption on an ideal Pt(111) surface [2]. We recently showed that at operating temperatures of conventional fuel cells, H+ transmission across the Pt-Nafion interface is unlikely without quantum effects and that the asymmetric nature of the barrier enhances transmission [3]. In more realistic systems, density functional theory-based calculations on a defective Pt(111) surface reveal hydrogen to be preferably adsorbed on bridge sites at the step edges of a vacancy, and is expected to have migration barrier above 30 meV [4]. On the other hand, compressive (tensile) strain prevents (promotes) H2 dissociation and subsequent H adsorption, while a CO neighbor only prevents H2 dissociation [5].
Partial results of our current calculations, based on the density-functional theory, reveal that vacancies on the substrate can significantly lower the barrier for the dissociative adsorption of H2 on the Pt(111) surface. We attribute this behavior to the increased reactivity of the surface as a result of the vacant sites. A more detailed discussion of these results will be conducted in the meeting.
[1] S. L. Bernasek and G. A. Somorjal, J. Chem. Phys. 62 (1975) 3149
[2] N. B. Arboleda Jr., H. Kasai, H. Nakanishi, and W. A. Diño: Thin Solid Films 509 (2006) 227
[3] N. B. Arboleda Jr., M. Tsuda, and H. Kasai: e-J. Surf. Sci. Nanotech. 4 (2006) 640
[4] T. A. Roman, H. Nakanishi, W. A. Diño, and H. Kasai: e-J. Surf. Sci. Nanotech. 4 (2006) 619
[5] M. Tsuda and H. Kasai: Jap. J. App. Phys. 45 (2006) L1219
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