Special Seminar, Dr. Vojislav Stamenkovic, Nov. 10
Nanocatalyst Engineering: From Well-Defined to Nanoscale Surfaces
Vojislav Stamenkovic
Argonne National Laboratory
Materials Science Division
Argonne, IL USA
Tuesday, November 10, 2009
2:00-3:00pm
Room 31-161
Ability to /tune the electronic and structural properties of nanocatalysts/ can potentially lead towards the superior catalytic enhancement that was reported for the Pt_3 Ni(111)-skin surface [1].
Fine tuning of the surface properties is usually done on extended well-defined surfaces in ultra-high vacuum. A number of surface sensitive tools could be utilized such as AES, LEIS and UPS before controlled transfer into real reaction environment. The single and polycrystalline crystalline well-defined surfaces have been used to benchmark the activity range that could be expected on Pt based electrodes. The knowledge accumulated from well-defined systems is further used to engineer nanoscale surfaces with designated composition and morphology.
It has been proposed that surface modifications induced by the second/third metal, and consequent catalytic enhancements could occur through the following effects: (1) /Electronic effect/, due to changes in the metallic d-band center position vs. Fermi level; and (2) /Structural effect/, which reflects relationship between atomic geometry, and/or surface chemistry, i.e., dissolution – surface roughening. In principle, different near-surface composition profiles have been found to have different electronic structures. Modification in Pt electronic properties alters adsorption/catalytic properties of corresponding materials. The most active systems for the electrochemical oxygen reduction reaction (ORR) are established to be the Pt‑skin near‑surface formation.
The similar levels of catalytic enhancement have been established for corresponding nanoscale materials. In addition to electronic properties we have found how catalytic activity could be affected by the arrangement of surface defects on nanoscale surfaces. Ability to control surface and near surface catalyst properties enables fine tuning of catalytic activity and stability of nanoscale surfaces.
[1] V. Stamenkovic, B. Fowler, B.S. Mun, G. Wang, P.N. Ross, C.A. Lucas, N.M. Markovic, /Science/ 315 (2007) 493-497.
[2] V. Stamenkovic, B.S. Mun, K.J.J. Mayrhofer, P.N. Ross, N.M. Markovic, J. Rossmeisl, J. Greeley, J.K. Nørskov, /Angewandte Chemie International Edition/ 45 (2006) 2897.
[3] V. Stamenkovic, B.S. Mun, M. Arenz, K.J.J. Mayrhofer, C. A. Lucas, G. Wang, P.N. Ross, N.M. Markovic, /Nature Materials/ 6 (2007) 241.
