Effect of the adsorption of atoms and molecules on the surface dipole of the surface: a DFT study

MARIANA ISABEL ROJAS; EZEQUIEL PEDRO MARCOS LEIVA

Nice, France

Congreso; 61th Meeting of the International Society of Electrochemistry; 2010

Effect of the adsorption of atoms and molecules on the surface dipole of thesurface: a DFT study M.I.Rojas, E.P.M. Leiva Unidad de Matemática y Física, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, 5000 Córdoba, Argentina. mrojas@fcq.unc.edu.ar   The catalytic activity of the some metallic surfaces deposited on solid electrolytes may be reversibly decreased or accelerated by means of the electrochemical pumping of ions to the catalyst/gas interface (c/g). When a conductor electrolyte likeis employed, the negative polarization of the electrode leads to the migration of strongly polarized metal atoms usually represented as. Thus, an effective double layer is established, modifying the work function of the metal exposed, and affecting the binding strength of reacting adsorbed molecules. The change in the surface dipole of the catalyst, becomes manifest in changes of the surface catalytic activity that are reversible and even predictable on the basis of models [1-3]. In a recent work, we have simulated the pumping of  atoms onto a  surface [4] as a function of the chemical potential applied. First, at very low coverages, the film presents a disordered structure, and at the film turns into astructure due to the strong repulsive lateral interaction between Na adatoms. This structure is the same as that observed by STM for Vayenas [2]. Although the simulations reflect the experimental results, the question arises of why the pumping ofonto the oxidized surface improves the catalytic activity of the surface towards certain type of reactions. Although a number of successful approaches exist, we aim an explanation in terms of first-principles calculations. In the present work, we study the changes of the surface dipole due to the adsorption of as well as,, molecules onto pristine or oxidized surfaces. We evaluate the change of the surface dipole by means of DFT calculations with spin polarization (sp) as implemented in SIESTA [5] and infer the influence produced by these adsorbates on some prototypical reactions   [1] C.G. Vayenas, S. Bebelis, I.V. Yentekakis, en: G. Erlt, H. Knötzinger, J. Weitcamp (Eds.) Handbook of Catalysis, VCH, Weinheim, 1997, p. 1310-1338. [2] C. Vayenas and S. Brosda, Solid State Ionics 154-155 (2002) 243. [3] G. Vayenas and S. Brosda and C. Pliangos, J. Catal. 216 (2003) 487. [4] M.I. Rojas, M.M. Mariscal, E.P.M. Leiva, submitted to Electrochimica Acta. [5] J. M. Soler, E. Artacho, J. D. Gale, A. García, J. Junquera, P. Ordejón, D. Sánchez-Portal, J. Phys.: Condens. Matter 14 (2002) 2745.