| AVS 58th Annual International Symposium and Exhibition | |
| Surface Science Division | Tuesday Sessions |
| Session SS-TuP |
| Session: | Surface Science Poster Session |
| Presenter: | Nguyen Tien Quang, Osaka University, Japan |
| Authors: | M.C. Escano, Osaka University, Japan N.T. Quang, Osaka University, Japan H. Nakanishi, Osaka University, Japan E. Gyenge, The University of British Columbia, Canada H. Kasai, Osaka University, Japan |
| Correspondent: | Click to Email |
We studied O2 chemisorption on Pt surface in the need to promote O2 activation. Activation, in this case, is defined as lowered activation barrier for O2 dissociation but minimized O adatom (Oad) binding energies; or a significantly stretched O-O bond in a loosely bound molecular O2. This kind of reaction is not easy to attain since O2 may present the same affinity to surface in its reaction path. However, such unique reaction is often sought in many electrochemical/chemical systems (i.e. fuel cell cathode catalyst, three-way automotive catalyst). Here, we show how the magnetic state of Pt can achieve this desired reaction. The model system involves a non-magnetic Pt layer pseudomorphically laid on top of magnetic surface (M=Fe(001), Co(001)). The ab-initio calculation based on spin-polarized density functional theory, suggests that the magnetic ground state of the system is a ferromagnetically coupled Pt-M layers[1]. The induced spin moment of 0.50μB in the Pt layer is in agreement with X-ray Magnetic Circular Dichroism (XMCD) [2]. The hybridization of Pt-5d with the M–3d states give characteristic exchange splitting similar to the spin-resolved inverse photoemission spectroscopy [3]. Using the Heisenberg spin Hamiltonian to determine the exchange interaction, we note that strong inter-layer coupling of the Pt-M spins gives a transition temperature of Pt layer higher than room temperature, in agreement with [2,3].
Potential energy surfaces obtained for O2 dissociative adsorption on ferromagnetic Pt layer show much lower activation barrier for dissociation and also lowered Oad binding energy. For molecular adsorption, the O2 vibrational frequency is lower on ferromagnetic Pt as compared to paramagnetic Pt, despite the much lower binding energies on the former. We note that spin effects played significant role rather than charge transfer effects on the over-all structure and binding of the O2 at transition state and on the surface [4]. This will be discussed in the meeting in terms of local density of states, charge transfer and spin density, and other parameters involved in the bonding and magnetic interactions.
References
1. MC. Escano, T.Q. Nguyen, H. Nakanishi, H. Kasai. J. Phys.: Condens. Matt. 21 (2009) 49221.
2. J .Lyubina, I, Opahle, M .Richter, O. Gutfleisch, K. Muller and L. Schultz Appl. Phys. Lett. 89 (2006) 032505
3. R. Bertacco and F. Ciccacci, Phys. Rev. B, 57 (1998) 96.
4. M.C. Escaño, H. Nakanishi and H. Kasai, J. Phys. Chem. A 113 (2009) 14302.